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Effect of chemical compositions on tensile behaviors of high pressure die-casting alloys Al-10Si-yCu-xMn-zFe
... However, the as-cast strengths of the currently available die-cast aluminium alloys are usually low, with a yield strength of ~130-170 MPa [8,9]. Explorations have been done to develop die-cast aluminium alloys with higher strength through the conventional micro alloying method, but the improvements are struggling limited and the improved yield strengths are still in the low level of 180-190 MPa [10][11][12][13]. ...
... Fig. 8b presents the tensile properties of the die-cast AlSiMgCu/TiB 2 composites after T6 heat treatment. The yield strength, UTS and elongation of the unreinforced alloy were 320 � 2 MPa, 423 � 2 MPa and 12.1 � 1.0%, [8][9][10][11][12][13], and it also demonstrates at least ~60% increase in UTS over the reported particle reinforcement die-cast aluminium composites [22,37,38]. The super high yield strength of more than 350 MPa and UTS of above 450 MPa in association with the ductility of 5.5% delivered by the 3.0 wt% TiB 2 reinforced composite are milestone mechanical properties for the high pressure die casting industry. ...
... Fig. 11b Fig. 11b. The corresponding FFT pattern in Fig. 11d verified that the TiB 2 nanoparticle had coherent interface with the α-Al matrix, and the crystal orientation relation (OR) between the TiB 2 nanoparticle and the α-Al matrix was Al(11-1)// TiB 2 (0001) and Al[011]//TiB 2 [11][12][13][14][15][16][17][18][19][20]. ...
The structural lightweight in automotive and other industries motivates the usage of high strength die-cast aluminium alloys. However, the improvements of die-cast aluminium alloys are struggling limited by conventional micro alloying, and the improved yield strengths are still in the low level of 180-190 MPa. Here, high performance die-cast AlSiMgCu/TiB 2 composite was fabricated through the reinforcement of TiB 2 nanoparticles and the latest developed cutting-edge super vacuum assisted high pressure die casting (HPDC) process. The composite with 3.0 wt% TiB 2 nanoparticles could deliver the milestone high hardness of 1.56 GPa, yield strength of 356 MPa, tensile strength of 457 MPa and an industrially applicable ductility of 5.5%. The composite was strengthened by TiB 2 nanoparticles and nanoscale Q 0 and θ 0 precipitates that all had highly coherent interfaces with the α-Al matrix, indicative of strong interfacial bonding. The implantation of TiB 2 nanoparticles also induced special grain refinement strengthening of the composite. The fabricated composite demonstrates ~90% increase in strength over the currently available alloys, and it is promising for industrial application.
... The composite with 3.5 wt% TiB 2 nanoparticles delivered the high hardness of 150.2 kg/mm 2 , yield strength of 351 MPa, tensile strength of 410 MPa, and the industrially applicable good ductility of 5.2%, after T6 heat treatment. The strengthening of the T6 heat treated composite was a result of both TiB 2 nanoparticles and nanoscale β′′ precipitates that had coherent interfaces with α-Al matrix, i.e., Al(11-1)//TiB 2 (0001), Al[011]//TiB 2 [11][12][13][14][15][16][17][18][19][20], Al[320]//β″(a-axis), Al[1-30]//β″(c-axis) and Al(020)//β″(b-axis). The T6 heat treated composite reinforced by 3.5 wt% TiB 2 showed ductile fracture. ...
... However, the as-cast strengths of the currently available die-cast automotive aluminium alloys are usually low, with a yield strength of 130-170 MPa [9,10]. Explorations have been done to develop diecast automotive aluminium alloys with higher strength by conventional micro alloying, but the improvements are struggling limited and the improved yield strengths are still in the low level of 180-190 MPa [11][12][13][14]. It is hard to meet the requirement of higher strength die-cast automotive aluminium alloys basing on the currently available alloys. ...
... The ductility of the as-cast 3.5 wt% TiB 2 reinforced composite was 5.5% under non-vacuum assisted HPDC, while the ductility of the composite improved to 6.6% under super vacuum assisted HPDC. The as-cast yield strength of the 3.5 wt% TiB 2 reinforced composite was 214 MPa, and it was at least 25 MPa higher than the as-cast yield strength of the currently available diecast aluminium alloys [9][10][11][12][13][14]. The T6 heat-treated composite reinforced 3.5 wt% TiB 2 demonstrated 17% increase in yield strength over the previously reported [27] T6 heat-treated die-cast AlSiMgMn alloy without particle reinforcement, and it also demonstrated 23% increase in yield strength over the T6 heat-treated A356 Al alloy reinforced by SiC particles [25], under vacuum assisted HPDC, as shown in Fig. 10d. ...
The global carbon emission reduction strongly requires high strength lightweight die-cast aluminium alloys in industry. Here die-cast AlSiMgMn–TiB2 composites with advanced mechanical performance were fabricated by the implantation of TiB2 nanoparticles. Super vacuum assisted high pressure die casting was applied to enable the T6
heat treatment of the composites, and the super vacuum of 20 mbar was achieved in the limited evacuation time of 1.6 s. The composites demonstrated good die castability within the addition of 3.5 wt% TiB2, while the composites
could not fill into the chill vent with the addition of N3.5 wt% TiB2. The composite with 3.5 wt% TiB2 nanoparticles delivered the high hardness of 150.2 kg/mm2 , yield strength of 351 MPa, tensile strength of 410 MPa, and the industrially applicable good ductility of 5.2%, after T6 heat treatment. The strengthening of the T6 heat treated composite was a result of both TiB2 nanoparticles and nanoscale β′′ precipitates that had coherent interfaces with α–Al matrix, i.e., Al(11-1)//TiB2(0001), Al[011]//TiB2[11-20], Al[320]//β″(a-axis), Al[1-30]//β″(c-axis) and Al(020)//β″(b-axis). The T6 heat treated composite reinforced by 3.5 wt% TiB2 showed ductile fracture.
... The composite with 3.5 wt% TiB 2 nanoparticles delivered the high hardness of 150.2 kg/mm 2 , yield strength of 351 MPa, tensile strength of 410 MPa, and the industrially applicable good ductility of 5.2%, after T6 heat treatment. The strengthening of the T6 heat treated composite was a result of both TiB 2 nanoparticles and nanoscale β′′ precipitates that had coherent interfaces with α-Al matrix, i.e., Al(11-1)//TiB 2 (0001), Al[011]//TiB 2 [11][12][13][14][15][16][17][18][19][20], Al[320]//β″(a-axis), Al[1-30]//β″(c-axis) and Al(020)//β″(b-axis). The T6 heat treated composite reinforced by 3.5 wt% TiB 2 showed ductile fracture. ...
... However, the as-cast strengths of the currently available die-cast automotive aluminium alloys are usually low, with a yield strength of 130-170 MPa [9,10]. Explorations have been done to develop diecast automotive aluminium alloys with higher strength by conventional micro alloying, but the improvements are struggling limited and the improved yield strengths are still in the low level of 180-190 MPa [11][12][13][14]. It is hard to meet the requirement of higher strength die-cast automotive aluminium alloys basing on the currently available alloys. ...
... The ductility of the as-cast 3.5 wt% TiB 2 reinforced composite was 5.5% under non-vacuum assisted HPDC, while the ductility of the composite improved to 6.6% under super vacuum assisted HPDC. The as-cast yield strength of the 3.5 wt% TiB 2 reinforced composite was 214 MPa, and it was at least 25 MPa higher than the as-cast yield strength of the currently available diecast aluminium alloys [9][10][11][12][13][14]. The T6 heat-treated composite reinforced 3.5 wt% TiB 2 demonstrated 17% increase in yield strength over the previously reported [27] T6 heat-treated die-cast AlSiMgMn alloy without particle reinforcement, and it also demonstrated 23% increase in yield strength over the T6 heat-treated A356 Al alloy reinforced by SiC particles [25], under vacuum assisted HPDC, as shown in Fig. 10d. ...
The global carbon emission reduction strongly requires high strength lightweight die-cast aluminium alloys in industry. Here die-cast AlSiMgMn–TiB2 composites with advanced mechanical performance were fabricated by the implantation of TiB2 nanoparticles. Super vacuum assisted high pressure die casting was applied to enable the T6 heat treatment of the composites, and the super vacuum of 20 mbar was achieved in the limited evacuation time of 1.6 s. The composites demonstrated good die castability within the addition of 3.5 wt% TiB2,while the composites could not fill into the chill vent with the addition of N3.5 wt% TiB2. The composite with 3.5 wt% TiB2 nanoparticles delivered the high hardness of 150.2 kg/mm2, yield strength of 351MPa, tensile strength of 410MPa, and the industrially applicable good ductility of 5.2%, after T6 heat treatment. The strengthening of the T6 heat treated composite was a result of both TiB2 nanoparticles and nanoscale β′′ precipitates that had coherent interfaceswithα–Al matrix, i.e., Al(11-1)//TiB2(0001), Al[011]//TiB2[11-20], Al[320]//β″(a-axis), Al[1-30]//β″(c-axis) and Al(020)//β″(b-axis).
The T6 heat treated composite reinforced by 3.5 wt% TiB2 showed ductile fracture.
... However, the as-cast strengths of the currently available die-cast aluminium alloys are usually low, with a yield strength of ~130-170 MPa [8,9]. Explorations have been done to develop die-cast aluminium alloys with higher strength through the conventional micro alloying method, but the improvements are struggling limited and the improved yield strengths are still in the low level of 180-190 MPa [10][11][12][13]. ...
... Fig. 8b presents the tensile properties of the die-cast AlSiMgCu/TiB 2 composites after T6 heat treatment. The yield strength, UTS and elongation of the unreinforced alloy were 320 � 2 MPa, 423 � 2 MPa and 12.1 � 1.0%, [8][9][10][11][12][13], and it also demonstrates at least ~60% increase in UTS over the reported particle reinforcement die-cast aluminium composites [22,37,38]. The super high yield strength of more than 350 MPa and UTS of above 450 MPa in association with the ductility of 5.5% delivered by the 3.0 wt% TiB 2 reinforced composite are milestone mechanical properties for the high pressure die casting industry. ...
... Fig. 11b Fig. 11b. The corresponding FFT pattern in Fig. 11d verified that the TiB 2 nanoparticle had coherent interface with the α-Al matrix, and the crystal orientation relation (OR) between the TiB 2 nanoparticle and the α-Al matrix was Al(11-1)// TiB 2 (0001) and Al[011]//TiB 2 [11][12][13][14][15][16][17][18][19][20]. ...
... In order to promote the mechanical and tribological properties of recycled Al alloys, more and more researches are focused on changing the morphologies of needle-like iron phases by adding the neutralized elements (i.e., Ti, Sr, B, Ce, Cr, etc.) [7,[11][12][13]. Among these neutralized elements, the manganese has been widely added into the secondary Al alloys due to the refinement and modification effect on needle-like phases [14,15]. Although the morphologies of needle-like phases could be remarkably changed by using manganese, the promotion of their mechanical properties were not prominent enough [11,13]. ...
... The EDS testing results given in Figure 7(a) indicate that the coarse dendrite-like phase is mainly composed of Fe and Mn elements. The XRD analysis suggests that the dendritelike phase might be the Al 85 (Mn 0.72 Fe 0.28 ) 14 Si phase. In addition, the Al 3.21 Si 0.47 (eutectic Al-Si) and the Al 86 Fe 14 existed. ...
Individual and combined addition of Ti and Ce on the recycled Al-Si-Cu-Fe-Mn alloy was conducted. The microstructures and tensile properties of these fabricated alloys were investigated. In the case of Ti or Ce which was individually added, the added amount was ranging from 0.03 wt.% to 0.09 wt.%. The combined addition of Ti and Ce was set at the ratios of 1 : 1, 1 : 3, and 3 : 1 with a total amount of 0.12 wt.%. Microstructures and phases of these alloys were investigated by using an optical microscope, X-ray diffraction testing, and SEM coupled with EDS. The morphologies of these alloys were quantified by analyzing the SDAS value, length of secondary phases, and phases' distribution uniformity. Tensile testing was carried out for understanding the strengthen effect of the modification process. Results show that the addition of Ce was favorable to the strength and
% elongation because the coarse needle-like phase and the polyhedral phase were effectively refined. Their SDAS values and distribution factor were remarkably declined with the increase of the Ce level. The Ti addition could also refine the secondary phases and SDAS values. But its effect was not as prominent as the addition of Ce. Combined addition of Ti and Ce elements at the ratio of 1 : 3 resulted in the samples reaching maximum comprehensive tensile properties. In this case, the short needle-like
phase was uniformly distributed in the microstructure. Few polyhedral phases could be found in the Al-Si-Cu-Fe-Mn matrix. The strengthening of these fabricated materials was due to the grain refinement for α-Al and modification for coarse secondary phases. In addition, distribution uniformity of secondary phases was also changed by their modification effects.
... According to Zhang et al. [50] hydrogen micropores are formed from hydrogen vacancy groups. Other studies [11,14] however, show that hydrogen micropores are heterogeneously Mackenzie [20] charge hydrogen blisters formed during heat treatment by transition to Al2O3 hydration AlOOH (boehmite) shows in Figure 6a, although this is not formed in solution temperature, although heating does not prevent this compound from being formed [48] shows that the formation of blisters that transform surface oxide into boehmite occurs at temperatures lower than that of solution. ...
... The necessity to enhance the utility properties of materials and increase the longevity of construction components has led research and development in various industrial branches, such as materials processing [1] or construction [2,3], towards the design of new materials and improving the performance of contemporary ones. Generally, enhancement of the mechanical and utility properties can be achieved via variations in the chemical composition of the particular material, as documented, for example, by Zhang et al. [4], and structural modifications (grain refinement), which was demonstrated also for pure and commercially pure metals [5,6]. Verlinden et al. claimed that grain refinement introduces lattice defects, such as dislocations and grain boundaries, which increase the materials' intrinsic energy and act as strengthening agents [7]. ...
This contribution characterizes the performance of a DESI 11 high-speed disintegrator working on the principle of a pin mill with two opposite counter-rotating rotors. As the ground material, batches of Portland cement featuring 6–7 Mohs scale hardness and containing relatively hard and abrasive compounds with the specific surface areas ranging from 200 to 500 m2/kg, with the step of 50 m2/kg, were used. The character of the ground particles was assessed via scanning electron microscopy and measurement of the absolute/relative increase in their specific surface areas. Detailed characterization of the rotors was performed via recording the thermal imprints, evaluating their wear by 3D optical microscopy, and measuring rotor weight loss after the grinding of constant amounts of cement. The results showed that coarse particles are ground by impacting the front faces of the pins, while finer particles are primarily milled via mutual collisions. Therefore, the coarse particles cause higher abrasion and wear on the rotor pins; after the milling of 20 kg of the 200 m2/kg cement sample, the wear of the rotor reached up to 5% of its original mass and the pins were severely damaged.
... 1.1.1 Non-heat-treated die-cast aluminum alloy Shanghai Jiao Tong University has developed two aluminum alloys for die castings, which are denoted as JDA1 (Al-Si-Mn-Mg-RE) [4] and JDA2 (Al-Mg-Si-Mn) [5]. These alloys do not need high-temperature solution treatment and artificial aging. ...
The microstructure, mechanical properties and thermal stability of high pressure die casting Al‐12Si‐Sc alloy with 0.1 wt% Sc addition were investigated. Compared with the commercial A380 alloy, the alloy shows a significant refinement of α‐Al and eutectic Si microstructure. Meanwhile, β‐Fe with irregular morphology shows a smaller size and lower volume fraction in Al‐12Si‐Sc alloy. Upon as‐cast state, the elongation of the alloy is improved to 6.7% with an ultimate tensile strength of 332 MPa, which is a better combination of ductility and strength in the literature. After thermal exposure at 200 °C for 200 h, it retains tensile strength of 277 MPa and holds the microhardness up to 90 HV even exposure for 1000 h. These excellent properties may widen the application of high pressure die casting Al‐Si alloy for cylinder block and cylinder head. This article is protected by copyright. All rights reserved.
Mechanical behavior and microstructure evolution of a newly developed high strength die casting Al–13Si-0.25Cu alloy (in wt%) were investigated under as-cast, peak-aged and thermal-exposed conditions. In the as-cast condition, the alloy has a yield strength (YS) of 213 MPa and an elongation (El) of 4.6% under as-cast condition. The alloy YS is further improved to 265 MPa after T5 ageing treatment. The enhancement of YS after ageing is attributed to the formation of nanoscale β″, Q′ and θ′ phase precipitates from the α-Al matrix. After thermal exposure at 350 °C for 100 hours, however, these precipitates mostly dissolve into the α-Al matrix and the ultrafine eutectic Si networks undergo breaking and coarsening, reducing YS to 117 MPa while enhancing the El to 10.3%.
Three new ultrafine hypoeutectic die-cast alloys based on quaternary Al-Cu-Si-Mg system were developed. The CALPHAD thermodynamic modelling of Al-Cu-Si-Mg system based on Scheil description was conducted to predict the volume fractions of the eutectic mixtures. The designed volume fraction of eutectic mixtures of Al-xCu-2.2Si-1.1Mg (x = 5, 6.6 and 10.6 wt%) alloys were determined to be 0.2, 0.25 and 0.3, respectively. With the increase in eutectic fraction, the yield strength and ultimate tensile strength increased from 219 MPa to 267 MPa, and 344.7 MPa–395 MPa respectively, while the elongation to fracture decreases from 7.72% to 3.4%. The microstructure of the alloys mainly consists of Si, Al2Cu, α-Al and Al4Cu2Mg8Si7 (Q) phases. The Al5Cu2.2Si1.1Mg and Al6.6Cu2..2Si1.1Mg alloys had similar microstructures that consisted of coarse binary/ternary and fine quaternary eutectic regions, surrounding α-Al matrix. The Al10.6Cu2.2Si1.1Mg alloy contained α-Al grains and almost only one type of eutectic structure. The orientation relationships among Al2Cu, α-Al and Q phases were found in the eutectic region. Al2Cu and α-Al has a coherent interface, while the interfaces between Q and Al2Cu as well as Q and α-Al, were found to be semi-coherent. Our results broaden a new approach to the design of die-cast alloys with multi-phase and multi-component microstructure for high-performance applications.
A high strength (Yield strength ! 320 MPa) and high ductility (Tensile elongation ! 10%) dieecast aluminium alloy was first developed. The AlSiCuMgMn alloy processed by high pressure die casting can provide the high yield strength of 321 MPa, the high ultimate tensile strength of 425 MPa and the high ductility of 11.3%, after solution treated at 510 C for 30 min and aged at 170 C for 12 h. The alloy demonstrated 150% increase in ductility over the reported most advanced dieecast aluminium alloy, also comparable tensile properties to the 6000 series wrought aluminium alloys but with much lower manufacturing cost. The asecast microstructure of the alloy mainly contained the primary a 1 eAl phase solidified in the shot sleeve, the secondary a 2 eAl phase solidified in the die, the AleSi eutectic phase and the intermetallic phases QeAl 5 Cu 2 Mg 8 Si 6 and qeAl 2 Cu. The intermetallic phases Q and q were dissolved into the aeAl matrix during solution. Nanoscale precipitates Q 0 and q 0 were precipitated from the aeAl matrix for the strengthening of the alloy through ageing treatment. Multiple effects resulted in the high ductility of the alloy.
High as-cast strength die-cast AlSi9Cu2Mg alloy was achieved with industrially acceptable ductility, via the addition of titanium diboride nanoparticles. The main intermetallic compounds in the die-cast AlSi9Cu2Mg alloy were identified as qeAl 2 Cu and QeAl 5 Cu 2 Mg 8 Si 6 phases. The Fe-rich compound formed in the present die-cast alloy with a high Mn/Fe ratio of 3:1 was determined as the BCC structured aeAl 15 (Fe,Mn) 3 Si 2 phase with a lattice parameter of a ¼ 1.2702 nm, and the Fe-rich compound had highly faceted morphology with {110} surface termination. The Al matrix phase in the die-cast AlSi9Cu2Mg alloy was refined by~65% from 18.1 mm to 6.4 mm, after adding 3.0 wt% titanium diboride nanoparticles. The titanium diboride nanoparticles in the alloy showed coherent interface with the Al matrix, with the (11-1) lattice face of Al parallel to the (0001) lattice face of titanium diboride. The as-cast AlSi9Cu2Mg alloy containing 3.0 wt% titanium diboride nanoparticles exhibited the high yield strength of 233 ± 3 MPa and the tensile strength of 398 ± 7 MPa, as well as the industrially acceptable elongation of 4.8 ± 0.7%, and it showed at least 23% improvement in the as-cast yield strength over the existing die-cast Al alloys. The strengthening by nanoparticle and coherent interface (~32 MPa) was higher than that by the refining of Al matrix (~10 MPa). The addition of titanium diboride nanoparticles also affected the fracture of the die-cast AlSi9Cu2Mg alloy, and cracks were prone to form in the Q and Fe-rich compounds , after the addition of titanium diboride nanoparticles.
The effects of Zn content on strength and wear performance of Al−12Si−3Cu alloy synthesized by gravity casting were systematically investigated. The microstructure and mechanical properties of the alloys were evaluated using OM, XRD, SEM as well as hardness, tension, compression and Charpy impact tests. Their dry sliding wear tests were carried out with a ball-on-disk tester. Microscopic examinations revealed that the microstructure of the base alloy consisted of the α(Al) dendrites, needle-type and coarse Si particles, and CuAl2 (θ) phase. The addition of Zn to this alloy resulted in the formation of α-solid solution phase and the increase of coarse Si particles. The hardness, yield, tensile and compressive strengths, elongation to fracture and impact toughness of the Al−12Si−3Cu−Zn alloys increased with increasing Zn content, but tendency in the tensile and compressive strengths and ductility reversed after adding 1.5%−2% Zn. In addition, the friction coefficient and volume loss of the Al−12Si−3Cu−Zn alloys decreased with increasing Zn content. The study showed that the addition of Zn to Al−12Si−3Cu alloy can improve its potential applications as tribological material.
In the present study, effects of Mn content on microstructure, hardness, tensile and dry sliding wear properties of eutectic Al–Si–Cu alloy in as cast-state were investigated. Mn addition to the eutectic alloy results in the formation of α-Al15Mn3Si2 phase in its microstructure. It was found that hardness of eutectic alloy increases continuously with increasing Mn content while its tensile strength and percentage elongation values decrease. It was also found that the friction coefficient and volume loss of eutectic alloy decrease as Mn content increases. Amongst the alloys, the lowest friction coefficient is obtained with Al–12Si–3Cu–2Mn alloy yet the Al–12Si–3Cu–1Mn alloy exhibits the highest wear resistance. Formation of adhesion layer, its oxidation and delamination were observed to be main wear mechanisms of Al–12Si–3Cu–(0–2)Mn alloys. These findings are explained in terms of formation of α-Al15Mn3Si2 phase, and its cracking tendency effect.
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A high strength (Yield strength ≥ 320 MPa) and high ductility (Tensile elongation ≥ 10%) die–cast aluminium alloy was first developed. The AlSiCuMgMn alloy processed by high pressure die casting can provide the high yield strength of 321 MPa, the high ultimate tensile strength of 425 MPa and the high ductility of 11.3%, after solution treated at 510 °C for 30 min and aged at 170 °C for 12 h. The alloy demonstrated 150% increase in ductility over the reported most advanced die–cast aluminium alloy, also comparable tensile properties to the 6000 series wrought aluminium alloys but with much lower manufacturing cost. The as–cast microstructure of the alloy mainly contained the primary α1–Al phase solidified in the shot sleeve, the secondary α2–Al phase solidified in the die, the Al–Si eutectic phase and the intermetallic phases Q–Al5Cu2Mg8Si6 and θ–Al2Cu. The intermetallic phases Q and θ were dissolved into the α–Al matrix during solution. Nanoscale precipitates Q′ and θ′ were precipitated from the α–Al matrix for the strengthening of the alloy through ageing treatment. Multiple effects resulted in the high ductility of the alloy.
In this study, the effect of holding pressure on microstructure and mechanical properties of low-pressure die cast A356 aluminum alloy was investigated. The results showed that the application of high holding pressure (300 kPa) generated castings with denser structure and superior mechanical properties. By increasing the holding pressure up to 300 kPa, the size of secondary dendrite arm spacing greatly reduced by 22.7% at the cooling rate of 1°C/s and decreased by 12.8% at 10°C/s. The Feret’s diameter and aspect ratio of eutectic silicon particles decreased by 8.4 and 5.1% at the cooling rate of 1°C/s and decreased by 9.3 and 6.4% at 10°C/s, respectively. Meanwhile, the density of A356 aluminum alloy increased to 2.678 g/cm³ and the area fraction of porosity decreased to 0.035%. Thus, tensile properties of A356 aluminum alloy obtained at high holding pressure were enhanced, especially the ductility. All these could be associated with the better filling capability and faster cooling rate caused by high holding pressure. In the analytical range of experimental conditions, the correlation of mechanical properties with process parameters was established by statistical models to predict the ultimate tensile strength and elongation of low-pressure die cast A356 aluminum alloy.
The first part of this study documented the as-aged microstructure of five cast aluminum alloys namely, 206, 319, 356, A356, and A356+0.5Cu, that are used for manufacturing automotive cylinder heads (Roy et al. in Metall Mater Trans A, 2016). In the present part, we report the mechanical response of these alloys after they have been subjected to various levels of thermal exposure. In addition, the thermophysical properties of these alloys are also reported over a wide temperature range. The hardness variation due to extended thermal exposure is related to the evolution of the nano-scale strengthening precipitates for different alloy systems (Al-Cu, Al-Si-Cu, and Al-Si). The effect of strengthening precipitates (size and number density) on the mechanical response is most obvious in the as-aged condition, which is quantitatively demonstrated by implementing a strength model. Significant coarsening of precipitates from long-term heat treatment removes the strengthening efficiency of the nano-scale precipitates for all these alloys systems. Thermal conductivity of the alloys evolve in an inverse manner with precipitate coarsening compared to the strength, and the implications of the same for the durability of cylinder heads are noted. © 2017 The Minerals, Metals & Materials Society and ASM International
In this paper, the effects of Zn on the microstructural evolution, hardness, and various characteristics of Al–20~45Zn–3Cu alloys were investigated. High-strength Al–Zn–Cu alloys (> 450 MPa) were fabricated by gravity casting without melt modification or heat treatment (i.e. T4~T6). Al-based alloys containing more than 20% Zn were designed for the gravity-casting process. In terms of the microstructure, as the amount of Zn addition in the alloys increased, the α-phase size decreased and the α + η non-equilibrium solidification-phase fraction increased. A complex network of eutectoid α + η, supersaturated η, and Cu-related intermetallic particles formed in the grain boundary regions. In addition, increasing the Zn content improved the mechanical properties of the alloys but reduced their damping capacity and toughness. The fractographic examination of the fracture surfaces indicated that the Al-Zn-Cu alloys with high Zn addition had fewer ductile dimple surfaces and more brittle cleavage surfaces.
This paper investigates the effects of strain rate and test temperature on the tensile properties and deformation behavior of a recently developed high-ductility cast aluminum alloy Al-5Mg-0.6Mn. The as-cast alloy tested at room temperature and the lowest strain rate of ~1.67×10-4s-1 shows the highest yield strength of ~212MPa, ultimate tensile strength of ~357MPa and elongation (~17.6%). Increasing strain rate reduces the ultimate tensile strength and ductility of the as-cast alloy. With the increasing of test temperature, the as-cast alloy shows significantly decreases in tensile strengths and improvements in elongation. The tensile failure of the alloy is mainly originated from the cracking and debonding eutectic particles. The Portevin-Le Chatelier effect occurs in the alloy tested at RT. Strain rate in current study ranges does not significantly affect the work-hardening behavior of the alloy. Increasing test temperature apparently reduces the strain-hardening exponent and coefficient. For the alloy tested at RT, all tensile failures occur prior to global instability, indicating the existence of localized damage. In contrast, for the alloy tested at HT, the global instability occurs at strains below the logarithmic fracture strains, suggesting that there is still a postnecking damage.
Permanent mold (PM) and high pressure die cast (HPDC) AlMg5Si2Mn are employed to investigate the microstructure, fatigue strength and corrosion resistance. Results indicated that the mechanical properties (R-m, R-0.2 and delta) of HPDC specimens (314 MPa, 189 MPa and 7.3%) are significantly better than those of PM specimens (160 MPa, 111 MPa and 2.5%) due to the finer grain size and less cast defects. Fatigue cracks of PM samples dominantly initiated from shrinkage pores and obscure fatigue striations are observed in crack growth region. Corrosion and pitting potentials of PM and HPDC AlMg5Si2Mn alloy are around -1250 mV, -760 mV and -1220 mV, -690 mV respectively. Numerous pits are observed around the grain boundaries because the corrosion potential of Mg2Si is more anodic than that of alpha-Al matrix. In addition, the superior corrosion resistance of HPDC samples can be attributed to the fine grain size and the high boundary density which improved the formation of oxide layer on the surface and prevented further corrosion.
This paper summarizes the melting and casting processes for magnesium alloys. It also reviews the historical development of magnesium castings and their structural uses in the western world since 1921 when Dow began producing magnesium pistons. Magnesium casting technology was well developed during and after World War II, both in gravity sand and permanent mold casting as well as high-pressure die casting, for aerospace, defense and automotive applications. In the last 20 years, most of the development has been focused on thin-wall die casting applications in the automotive industry, taking advantages of the excellent castability of modern magnesium alloys. Recently, the continued expansion of magnesium casting applications into automotive, defense, aerospace, electronics and power tools has led to the diversification of casting processes into vacuum die casting, low-pressure die casting, squeeze casting, lost foam casting, ablation casting as well as semi-solid casting. This paper will also review the historical, current and potential structural use of magnesium with a focus on automotive applications. The technical challenges of magnesium structural applications are also discussed. Increasing worldwide energy demand, environment protection and government regulations will stimulate more applications of lightweight magnesium castings in the next few decades. The development of use of Integrated Computational Materials Engineering (ICME) tools will accelerate the applications of magnesium castings in structural applications.
Standard mechanical test bars with a diameter of 6.4 mm and a gauge length of 50 mm were processed, and the microstructures of die cast AM60B alloy under different die casting process parameters were observed. The influences of the slow shot speed, the fast shot speed and the biscuit thickness on the externally solidified crystals (ESCs) were investigated. With the increase of the biscuit thickness, the number of the ESCs in the cast samples decreases. Under a low slow shot speed, larg ESCs are found in the cast structure and a high fast shot speed results in more spherical ESCs. The relationships between ESCs and process parameters were also discussed.
The effect of chromium concentration on the microstructure and mechanical properties of a high-pressure die-cast AlSi9Cu3(Fe) alloy is reported. The Cr content ranges within the composition tolerance limits of the standard EN AB-46000 alloy, from 0.057 up to 0.15wt.%. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes occurring with Cr addition. The results indicate that the morphology of the primary and proeutectic α-Alx(Fe,Mn,Cr)ySiz intermetallics are mainly polyhedral, star-like and blocky. The area fraction and the size of intermetallic compounds increases as the Cr content increases. At the holding temperature used for the different EN AB-46000 type alloys, sludge forms mainly in the shot sleeve before the melt entered the die cavity and segregates in the central region of the cross-section of the castings. The entrapped sludge, whose value can be estimated from the sludge factor by a linear relationship, affects the ultimate tensile strength and the ductility of the alloy at the highest Cr level.
High cycle fatigue properties of high-pressure die-cast magnesium alloys AZ91 hp, AM60 hp, AE42 hp, AS21 hp and of similarly produced cast aluminium alloy AlSi9Cu3 have been investigated. Ultrasonic fatigue tests up to 109 cycles show mean fatigue limits of approx. 38–50 MPa (magnesium alloys) and 75 MPa (AlSi9Cu3) in the tested casting condition. Fatigue cracks initiated at porosity in 98.5% of the samples. Considering porosity as initial cracks, specimens fail, if critical stress intensity amplitude, Kcr is exceeded. Kcr of the magnesium alloys range from 0.85±0.05 to 1.05±0.05 MPa√m, and 1.85±0.10 MPa√m was found for AlSi9Cu3. Below Kcr, fatigue cracks may initiate at porosity, however, do not propagate until failure. Using Kcr, the statistical distribution of defects is linked to the fracture probability at different stress amplitudes.
This monograph summar Steel and Alloy during many decades in part together with Alcoa Inc. The research covered areas of the structure, properties, thermal resistance, corrosion and fatigue of aluminum alloys in industrial manufacturing. · Emphasis on interconnection among phase equilibria, thermodynamics and microstructure of alloys; · Systematic overview of all phase diagrams with Al that are important for the development of casting aluminium alloys · Diagrams ("processing windows") of important technological properties such as castability, molten metal fluidity, tendency to hot pre-solidification cracking, porosity · Mathematical models for alloy mechanical properties facilitating the down-selection of best prospect candidates for new alloy development · New principles of design of eutectic casting aluminium alloys · Examples of successful novel casting alloy development, including alloys for high-strength applications, alloys with transition metals, and novel alloys utilizing aluminium scrap.
This chapter aims to trace a short history of the logical steps which led to the development of new aluminium materials for automotive applications. The main focus is on high-pressure die-cast (HPDC) aluminium alloys and the driving factors leading to the current use of premium casting alloys. The chemical composition, mechanical properties and specific features of Silafont®-36, Magsimal®-59 and Castasil®-37 are described, with guidelines provided for their processing and casting. Data from practical experiences are reported, answering the most common questions on primary low-iron ductile alloys. Finally, examples of the applications of these materials are briefly described, underlining the innovative aspect of each component.
This book has the stated aim of covering the physical and mechanical metallurgy, interfacial physics and mechanics, and processing of metal matrix composites (MMCs). The term metal matrix composites covers particle, short-fiber, and continuous-fiber reinforced metals. The book covers most of the important topics relevant to the mechanical characteristics of MMCs such as load transfer from the matrix to the fiber, plastic deformation of the metal matrix, effect of thermal mismatch between the fiber and the matrix, and microstructural changes in the matrix caused by the presence of reinforcements. Fracture, transport properties, environmental properties, and tribological characteristics of MMCs are dealt with. Analytical treatments of various topics are provided in a very able manner. The last two chapters include practical information on special techniques such as MMC specimen preparation for transmission electron microscopy, etc. and commercial applications of MMCs. What is surprising is that among the applications of MMCs, no mention is made of filamentary superconductors, conventional or high [Tc] ceramic oxide superconductors. This book is a welcome addition to the literature on metal matrix composites. It is suitable for scientists, engineers, and practicing engineers who deal with metal matrix composites. There is a wealth of line diagrams, micrographs, andmore » references to the literature, and there are subject and author indexes.« less
A method was developed for simultaneous determination of the migration of 28 kinds of primary aromatic amines(PAAs) from food contact materials by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The analytes were separated on a C-3 column, eluted by gradient with methanol and water, identified by electrospray ionization mass spectrometry in positive mode using multiple reaction monitoring (MRM), quantified by external standard method. The limits of detection (LOD, S/N = 3) and quantification (LOQ, S/N = 10) of 28 PAAs were 0.02-0.3 mu g/kg and 0.1-1.0 mu g/kg, respectively. The correlation coefficients of linear calibration curve were over 0.9915 in the ranges varied from 1.0 mu g/L to 1000 mu g/L. The recoveries of PAAs were 77.8%-105.3% in the spiked range of 1.0-100 mu g/kg, and the relative standard deviation (RSD) was 4.5%-11.8%. The experiment results indicated that the method was simple, rapid, sensitive, accurate, and could meet the correlative requirements for determination.
In order to assess the high-temperature performance of aluminum–silicon alloy reinforced with titanium diboride particles as potential piston material, the tensile behaviors and fracture mechanisms of in situ 4 wt% TiB2/Al–Si composite were investigated in the temperature range 25–350 °C. The tensile results revealed that the composite exhibited higher modulus than the matrix alloy at all testing temperatures, but both the matrix alloy and the composite presented similar strength levels above 200 °C. The ductility of the composite was found to be lower than that of the unreinforced matrix alloy at 25 and 200 °C, but no obvious distinction was observed at 350 °C. The effects of temperature and the presence of TiB2 particles on tensile properties of the composite had been evaluated. Fractographic morphology studies were done using scanning electron microscope, which indicated that the fracture of the composite altered from brittle to ductile mode with temperature increasing. At 25 and 200 °C, fracture was dominated by cracked silicon particles and separated TiB2 particles, while decohesion at particle–matrix interface was prevalent at 350 °C. Analysis of the fracture surfaces also showed that regions of clustered TiB2 particles were found to be the locations prone to damage in the composite at both room and high temperatures.
A refined microstructure of Al-Mg-Sc-Zr alloy with an average grain size of ~3.7 μm and a portion of high angle boundaries of 69.2% was produced by free forging. Excellent superplastic ductility of ≥500% was achieved at a wide temperature range of 450~500 °C and relatively high strain rate range of 1×10−3~5×10−2 s−1 in the Al-Mg-Sc-Zr alloy. A maximum elongation of 1593% was obtained at 475 °C and 1×10−3 s−1. Moreover, the electron back scattered diffraction (EBSD) and the transmission electron microscopy (TEM) analyses showed that the excellent superplasticity can be attributed to the high fraction of high angle grain boundaries and the presence of Al3(Sc,Zr) dispersoids in the Al-Mg-Sc-Zr alloy microstructure. The analyses on the superplastic data revealed the presence of threshold stress, the coefficient of strain rate sensitivity of 0.5, and an activation energy of 83.9 kJ/mol-1. It indicated that the dominant deformation mechanism was grain boundary sliding. Based on this notion, a constitutive equation for Al-Mg-Sc-Zr alloy has been developed.
Fracture of Al2O3 particles in an Al2O3 particle/ aluminum alloy metal matrix composite (MMC) under plastic straining was observed by in-situ tensile testing in a scanning electron microscope. The fracture of larger sized particles was found to be preferred to that of smaller sized ones for a given plastic strain. The Young’s modulus (Ec) of plastically strained MMC was reduced with increase in plastic strain (εp). The analytical model based on Eshelby’s equivalent inclusion method was constructed to explain the relationship between Ec and εp, resulting in a good agreement with the experimental results.
In this paper, the influence of La addition on the aging behavior, microstructure, mechanical properties, and thermal-resistant properties of Al–Mg–Si–Zr aluminum alloy has been studied with the help of optical microscope (OM), Brinell hardness measurements and scanning electron microscopy (SEM) equipped with energy dispersive spectrum (EDS). The results show that La addition decreases the peak-aged hardness during aging process. Electrical conductivity and thermal-resistant properties improve when the La addition exceed 0.2%. Increasing La content to 0.3% leads to a poor elongation at fracture. Most of La element exists in the form of compounds containing Si which result in improvement in thermal-resistant properties. The tensile strength of the material with 0.2% La addition reduces while the thermal-resistant properties and electrical conductivity improve. This amount of La addition added to the experimental alloy could be a compromise between the mechanical properties and others like electrical conductivity and thermal-resistant properties.
A high strength Al–Mg2Si–Mg–Zn based alloy has been developed for the application in high pressure die casting to provide improved mechanical properties. The effect of various alloying elements on the microstructure and mechanical properties including yield strength, ultimate tensile strength and elongation of the alloy was investigated under the as-cast and heat-treated conditions. The typical composition of the high strength alloy has been optimised to be Al–8.0 wt%Mg2Si–6.0 wt%Mg–3.5 wt%Zn–0.6 wt%Mn (Al–11.0 wt%Mg–2.9 wt%Si–3.5 wt%Zn–0.6 wt%Mn) with unavoidable trace impurities. The mechanical properties of the alloy were enhanced by a quick solution treatment followed by ageing treatment. The improved tensile properties were at a level of yield strength over 300 MPa, the ultimate tensile strength over 420 MPa and the elongation over 3% assessed using international standard tensile samples made by high pressure die casting. The microstructure of the die-cast alloy consisted of the primary α-Al phase, Al–Mg2Si eutectics, AlMgZn intermetallics and α-AlFeMnSi intermetallics under the as-cast condition. The AlMgZn intermetallic compound was dissolved into the Al-matrix during solution treatment and subsequently precipitated during ageing treatment for providing the effective improvement of the mechanical properties.
The super ductile diecast aluminium alloys have been developed particularly for application in
automotive body structure. On the basis of the reviewing aluminium alloys currently available, the
requirement of diecast aluminium alloys is summarized and the Al-Mg-Si system is focused in the
development. The effect of various alloying elements on the microstructure and the mechanical
properties, such as yield strength, ultimate tensile strength and elongation is assessed. The optimized
composition of the super ductile Al–Mg–Si alloy has been found to be at 5.0–5.5 wt% Mg, 1.5–2.0 wt% Si,
0.5–0.7 wt% Mn, 0.15–0.2 wt% Ti with Fe o0.25 wt% for the best combination of strength and ductility,
which shows 150 MPa of yield strength, 300 MPa of ultimate tensile strength, and 15% of elongation
under as-cast condition. The paint baking hardenability of the optimized alloy is found to be
insignificant. Less than a 10% increase in the yield strength was achieved, with a slight decrease in
the elongation after aging at 180 1C for 30 min, which is a simulated process of paint baking. Cu is found
to slightly increase the yield strength under the as-cast condition and after the heat treatment, but with
a significant reduction in the ductility. Therefore, Cu should be limited in the super ductile aluminium
alloy. The microstructure of diecast aluminium alloys at the optimized composition consists of the
primary a-Al phase, the a-AlFeMnSi intermetallics and the Al–Mg2Si eutectics. There are two types of
primary a-Al phase: dendritic or fragmented dendritic a-Al phase solidified in the shot sleeve and
globular a-Al particles solidified in the die cavity. The a-AlFeMnSi intermetallics is in the form of
compact morphology and with a size of less than 3 mm. The eutectic cells are at size of 10 mm with a
typical lamellar morphology of a-Al phase and Mg2Si phase.
Thermal analysis and interrupted quench experiments have been carried out to study the formation of β-FeSiAl5 and (BeFe)-BeSiFe2Al8 phases in Al7Si0.3Mg alloy with and without Be addition. In the base alloy with 0.6% Fe (without Be addition), a needle- and plate-shaped β-phase is present in the interdendritic regions and is formed by a ternary eutectic reaction. In the Be-added alloy with 0.6% Fe, a BeFe phase of Chinese script and polygon shapes grows along with the primary α-Al dendrites, leading to superior mechanical properties. It is proposed that this BeFe phase is formed by a peritectic reaction. Be addition has also resulted in some grain refinement.
The effects of rare earth erbium (Er) additions (0, 0.3, 0.6 and 0.9 wt.%) on the microstructure development and tensile properties of die-cast ADC12 aluminum alloy have been investigated in the present work. The microstructures and fracture surfaces of die-cast samples were examined by optical microscopy and scanning electron microscopy (SEM). It was found that the secondary dendrite arm spacing (SDAS) will decrease with increasing Er content, as the Er content increases to 0.6%, the lowest SDAS was obtained. In addition, the Er modified the eutectic silicon from a coarse plate-like and acicular structure to a fine branched and fibrous one. The microhardness of die-casted alloys were measured, the microhardness corresponding to the die-casted samples with 0, 0.3, 0.6 and 0.9 wt.% Er additions are 100.6, 107.1, 113.6 and 108.5 Hv, respectively. The tensile properties were improved by the addition of Er, and a good ultimate tensile strength (269 MPa) but poor elongation (2%) were obtained when the Er addition was 0.6 wt.%. Furthermore, fractographic examinations revealed that refined pore and spheroidized α-Al dendrite were responsible for the high ultimate tensile strength.
Deformation behavior of Al–6.2%Cu–0.6%Mg alloy and Al–6.2%Cu–0.6%Mg alloy containing 0.06wt.% of Sn was studied by hot compression tests conducted at various temperatures and strain rates. During the deformation process, the flow stress of the Al–Cu–Mg alloy increased due to trace addition of Sn. The peak flow stress for both the alloys increased with increase in strain rate and decrease in deformation temperature. The peak flow stress during deformation can be correlated with temperature and strain rate by a hyperbolic-sine equation. The activation energy for hot deformation of the Al–Cu–Mg alloy was determined to be 183.38kJ/mol, which increased to 223.30kJ/mol when micro-alloyed with 0.06wt.% of Sn. The Zener–Hollomon (Z) parameter for the two alloys was determined for the various deformation conditions. The tendency of dynamic recrystallization increases with low strain rates and high deformation temperatures which correspond to low Z values. The hot deformation behavior of both the alloys was modeled by suitable constitutive equation. The peak flow stresses at various deforming conditions have been predicted and correlated with the experimental values. It was possible to predict 80% of the values for peak flow stress within an error less than ±11.5% for Alloy-A, where as for Alloy-B, 95% of the peak flow stress values could be predicted within an error of ±7%.
The high-temperature tensile properties and microstructural evolution of Al–6Mg–0.4Sc–0.13Zr alloy prepared by conventional cold rolling at various temperatures were studied. At 573K, the Al3(ScxZr1−x) particles stabilized the extremely fine subgrains (SG) and submicrograins (SMG). These SG and SMG boundaries acted as effective dislocation sinks, turning into true high-angled boundaries susceptible to consequent sliding. Therefore, the alloy achieved an acceptable ductility with 300% elongation. At 623–723K, because geometrical sliding was not feasible with rugged grain boundaries and dislocation movement was strongly hindered by the Al3(ScxZr1−x) particles, the alloy exhibited poor ductility. At 773 and 803K, the Al3(ScxZr1−x) particles began to act as grain stabilizers, and retained fine-grain structure at these high temperatures. As a result, a maximum elongation of 1100% was achieved after deformation at 803K with a strain rate of 5×10−3s−1.
In this investigation, an effective approach based on multivariable linear regression (MVLR) and genetic algorithm (GA) methods has been developed to determine the optimum conditions leading to minimum porosity in AlSi9Cu3 aluminium alloy die castings. Experiments were conducted by varying holding furnace temperature, die temperature, plunger velocities in the first and second stage, and multiplied pressure in the third stage using L27 orthogonal array of Taguchi method. The experimental results from the orthogonal array were used as the training data for the MVLR model to map the relationship between process parameters and porosity formation of the die cast parts. With the fitness function based on this model, genetic algorithms were used for the process conditions optimization. By comparing the predicted values with the experimental data, it was demonstrated that the proposed model is a useful and efficient method to find the optimal process conditions in pressure die casting associated with the minimum porosity percent.
The zinc die casting process is undergoing major changes as researchers uncover new knowledge about the material and the process. International Lead Zinc Research Organisation, Inc. (ILZRO) has been sponsoring such research for years in the U.S., U.K. and Australia. The basic objective of these projects is to improve the zinc die casting process itself so that ultimately all major parameters in the process will be controlled automatically to enable production of zinc die castings at the lowest possible cost and with zero defects. This paper reviews some of the specific developments emerging from all three research areas, including thin-walled die casting, alternative gating systems, die coatings and die materials, pressure and thermal studies, metallurgical properties of castings, and runner design, with emphasis on tapered runners.
The influence of casting defects on static and fatigue strength is investigated for a high pressure die cast aluminium alloy. Defects exist in gas and shrinkage pores as well as cold fills, dross and alumina skins. For the three batches of specimens, differing for the sprue–runner design, the influence was straightforward, while no significant variation in the fatigue strength was observed when looking at batches of “acceptable” and “non-acceptable” components, as judged within the foundry quality control. In this case, defects count for their size and location, while quality control often takes no account for component working conditions. The Haigh diagram shows a good matching between the specimen reference material and the component fatigue data.
The elastic-plastic deformation behavior of particulate reinforced metal matrix composites is strongly influenced by not only properties of the metal matrix and reinforcement but also microstructural parameters such as particle size, volume fraction, reinforcement shape and topology that are dependent on the particular processing route used to fabricate the materials. Nan and Clarke have recently developed a hybrid, analytical model by incorporating essential features of both continuum plasticity and dislocation plasticity, which is a combination of the key features of dislocation plasticity with a continuum mechanics approach based on effective medium approximations (EMA). In the present contribution, particular attention will be paid to two problems on the hybrid model. Firstly, the authors introduce a volume-weighted averaging procedure in Nan and Clarke`s methodology and then re-estimate the effect of particle size distribution on deformation in the case of both no damage and including particle fracture. For illustrative and quantitative purposes, the calculations are compared with the experimental results on particular SiC-Al composite by Lloyd. Secondly, the difference between the deformation, secant and the incremental, tangent modulus approaches chosen for EMA modeling is addressed.
The dissolution and melting of Al2Cu phase in solution heat-treated samples of unmodified Al-Si 319.2 alloy solidified at ≈10 °C were studied using optical
microscopy, image analysis, electron probe microanalysis (EPMA), and differential scanning calorimetry (DSC). The solution
heat treat-ment was carried out in the temperature range 480 °C to 545 °C for solution times of up to 24 hours. Of the two
forms of Al2Cu found to exist,i.e., blocky and eutectic-like, the latter type is more pronounced in the unmodified alloy (at ≈10 °C) and was observed either
as separate eutectic pockets or precipitated on preexisting Si particles, β-iron phase needles, or the blocky Al2Cu phase. Dissolution of the (Al + Al2Cu) eutectic takes place at temperatures close to 480 °C through frag-mentation of the phase and its dissolution into the
surrounding Al matrix. The dissolution is seen to accelerate with increasing solution temperature (505 °C to 515 °C). The
ultimate tensile strength (UTS) and fracture elongation (EL) show a linear increase when plotted against the amount of dissolved
copper in the matrix, whereas the yield strength (YS) is not affected by the dissolution of the Al2Cu phase. Melting of the copper phase is observed at 540 °C solution temperature; the molten copper-phase particles transform
to a shiny, structureless phase upon quenching. Coarsening of the copper eutectic can occur prior to melting and give rise
to massive eutectic regions of (Al + Al2Cu). Unlike the eutectic, fragments of the blocky Al2Cu phase are still observed in the matrix, even after 24 hours at 540 °C.
The plastic deformation behavior of aluminum casting alloys A356 and A357 has been investigated at various solidification
rates with or without Sr modification using monotonic tensile and multi-loop tensile and compression testing. The results
indicate that at low plastic strains, the eutectic particle aspect ratio and matrix strength dominate the work hardening,
while at large plastic strains, the hardening rate depends on secondary dendrite arm spacing (SDAS). For the alloys studied,
the average internal stresses increase very rapidly at small plastic strains and gradually saturate at large plastic strains.
Elongated eutectic particles, small SDAS, or high matrix strength result in a high saturation value. The difference in the
internal stresses, due to different microstructural features, determines the rate of eutectic particle cracking and, in turn,
the tensile instability of the alloys. The higher the internal stresses, the higher the damage rate of particle cracking and
then the lower the Young’s modulus. The fracture strain of alloys A356/357 corresponds to the critical amount of damage by
particle cracking locally or globally, irrespective of the fineness of the microstructure. In the coarse structure (large
SDAS), this critical amount of damage is easily reached, due to the clusters of large and elongated particles, leading to
alloy fracture before global necking. However, in the alloy with the small SDAS, the critical amount of damage is postponed
until global necking takes place due to the small and round particles. Current models for dispersion hardening can be used
to calculate the stresses induced in the particles. The calculations agree well with the results inferred from the experimental
results.
Microstructural evolution under intensive forced convection is of importance to the development of new semisolid processing
technologies. Although efforts have been made to understand the nucleation and growth behavior of the primary phase under
forced convection, important aspects of microstructural evolution still remain as open questions. Experimental work was undertaken
to investigate the effects of a high shear rate and high intensity of turbulence on the solidification behavior of a Sn-15
wt pct Pb alloy using a twin-screw extruder. It was found that increasing the shear rate and intensity of turbulence can give
rise to substantial grain refinement, which can be attributed to the increased effective nucleation rate caused by the extremely
uniform temperature and composition fields in the bulk liquid at early stages of solidification. It was also found that forced
convection increases the growth velocity and stabilizes the solidification interface, resulting in a transition of the growth
morphology from rosette to spheroid with increasing shear rate and intensity of turbulence. Discussions are made on the effects
of flow conditions on the nucleation behavior, constitutional undercooling, stability of the solidification interface, and
growth morphology.
The automotive business is an ideal choice to examine the dramatic impact of improved materials and manufacturing processes on an industry Automakers today are able to combine high-tech materials originally applied in aerospace and other industries with the high-volume manufacture of a mass-marketed consumer product. This paper will detail how many of the changes to vehicles that have resulted from these influences over the past 50 years have been enabled by significant advances in materials and processes.
Constant-amplitude high-cycle fatigue tests (σmax=133 MPa, σmax/σy=0.55, and R=0.1) were conducted on cylindrical samples machined from a cast A356-T6 aluminum plate: The fracture surface of the sample with the smallest fatigue-crack nucleating defect was examined using a scanning electron microscope (SEM). For low crack-tip driving forces (fatigue-crack growth rates of da/dN<1 × 10−7 m/cycle), we discovered that a small semicircular surface fatigue crack propagated primarily through the Al-1 pct Si dendrite cells. The silicon particles in the eutectic remained intact and served as barriers at low fatigue-crack propagation rates. When the semicircular fatigue crack inevitably crossed the three-dimensional Al-Si eutectic network, it propagated primarily along the interface between the silicon particles and the Al-1 pct Si matrix. Furthermore, nearly all of the silicon particles were progressively debonded by the fatigue cracks propagating at low rates, with the exception of elongated particles with a major axis perpendicular to the crack plane, which were fractured. As the fatigue crack grew with a high crack-tip driving force (fatigue-crack growth rates of da/dN>1 × 10−6 m/cycle), silicon particles ahead of the crack tip were fractured, and the crack subsequently propagated through the weakest distribution of prefractured particles in the Al-Si eutectic. Only small rounded silicon particles were observed to debond while the fatigue crack grew at high rates. Using fracture-surface markings and fracture mechanics, a macroscopic measure of the maximum critical driving force between particle debonding vs fracture during fatigue-crack growth was calculated to be approximately K
maxtr
≈6.0 MPa √m for the present cast A356 alloy.
Phase equilibria in the Al corner of the Al-Fe-Mn-Si system at 550 °C have been explored. Twenty-six quaternary alloys were
prepared and analyzed by microprobe analysis. Elemental powders were mixed under air and molten at 1000 °C under argon flux.
These specimens received a heat treatment at 550 °C during 4 to 12 weeks and finally were water quenched. A four-phase region,
where Al, Si,α-Al(Fe,Mn)Si, andβ-Al(Fe,Mn)Si are in equilibrium with each other, was found. The presence of a single-phaseα-Al(Fe,Mn)Si region, starting in the Al-Mn-Si subsystem and extending toward the Al-Fe-Si subsystem, could be confirmed. Some
problems concerning the fit of the quaternary system with its ternary Al-Fe-Mn subsystem remain to be solved.
The tensile fracture behavior of a cast and extruded 2014 aluminum alloy metal matrix composite (MMC) reinforced with 10, 15, and 20 vol.% aluminum oxide particles was investigated as a function of temperature between 100 and 300°C and hold time, and compared with the unreinforced alloy. In addition, the effect of aging condition was investigated in a 15 vol.% composite tested at 200°C. At lower temperature the composites have higher yield strength and UTS than the unreinforced material, and both decrease with increasing temperature. At higher temperatures all the materials have similar strength levels. The elongation is lower in the composites, decreasing with increasing level of reinforcement and increasing with increasing temperature, except at the highest temperature where all the composites are about the same. The microstructural damage in the composites also varies with temperature: particle fracture dominates at lower temperatures and interparticle voiding is the main damage feature at elevated temperatures. The time at temperature, and hence the degree of overaging, has little effect on the observed trends in the composite, in contrast with the unreinforced material where the density of voids decreases with increasing hold times. The transition temperature where the major damage changes from particle cracking to interparticle voiding increases with volume fraction and particle size, and decreases with overaging. The cracked particle density and void density both increase with strain, and the highest rate of increase occurs in the overaged material. In general, the tendency for particle cracking is reduced and for interparticle voiding is increased by any factor which permits accomodation of strain by the matrix, such as lower volume fraction of particles, small particle size, nonclustered particle distribution, and matrix softening from underaging or overaging.
The effects of particle volume fraction and matrix temper on the flow and fracture characteristics of a series of particle-reinforced metal matrix composites under tensile and compressive loadings have been examined. Under compressive loading, a steady-state regime is attained in which the composite flow stress is proportional to the matrix flow stress at the same level of strain. The strength enhancement associated with the particles increases with increasing particle content and the matrix hardening exponent. The trends are consistent with predictions of finite element calculations of unit cell models, treating the particles as either spheres or cylinders with unit aspect ratio. Under tensile loading, the particles crack at a rate dependent on the intrinsic strength characteristics of the particles as well as the flow characteristics of the matrix. Particle cracking causes local softening, which reduces the work hardening rate as compared with compression deformation. This lowers both the strength and the ductility. Experimental measurements have been combined with finite element calculations to develop a damage law, incorporating the effects of the matrix strength on the particle stress. The damage law has been used to simulate the tensile flow response of the composites, using appropriate cell models under either isostrain or isostress conditions. Though the trends obtained from the simulations are in qualitative agreement with the experimental results, they tend to underestimate the flow stress. In all cases, tensile fracture is preceded by the formation of a neck. The condition at the onset of necking is consistent with the Considère criterion. Differences in necking strains between the composites and the monolithic matrix alloy have been rationalized on the basis of the rate of damage accumulation.
A systematic study of the effect of microstructural parameters on the fracture behaviour of silicon carbide particle reinforced aluminium matrix composites has been carried out. Acoustic emissions have been monitored during tensile testing, giving the size and number of emmissions as a function of strain. This has been shown to be simply related to the rate of void nucleation at the reinforcing phase. Both particle fracture and particle/matrix decohesion mechanisms can be detected. Void nucleation was observed from the onset of plastic deformation and a linear relationship between damage initiation rate and strain was found. The rate of emission increased with reiforcing particle size and volume fraction but was independent of matrix alloy composition and heat treatment. These results show that the failure strain of particulate metal matrix composites is not controlled solely by the onset of void nucleation at the reinforcing phase. Local failure processes in the matrix are shown to promote void coalescence and dominate the ductility. However, suppression of void nucleation at the particles increases the ductility. It is suggested that a critical number of fractured particles is required before failure.
Lightweight magnesium alloys are being increasingly used in automotive and other transportation industries to achieve energy efficiency and environmental protection. Design of magnesium components requires low cycle fatigue (LCF) behavior since these applications are often subjected to cyclic loading and/or thermal stresses. The objective of this investigation was to study the cyclic deformation behavior and LCF life of a large solid extruded section of AZ31 magnesium alloy. It was observed that the alloy was cyclically stable at lower strain amplitudes and exhibited cyclic hardening characteristics at higher strain amplitudes, with a cyclic hardening exponent of about 2.6 times higher than the monotonic strain hardening exponent. A relationship between the plastic strain amplitude and the number of cycles (N), was observed. With increasing total strain amplitude both plastic strain amplitude and mean stress increased and the fatigue lifetime decreased. Bauschinger effect was pronounced at higher strain amplitudes, resulting in asymmetric hysteresis loops due to twinning in compression during unloading and subsequent detwinning in tension during loading. Modulus during cyclic deformation was constant at the low strain amplitude, but it decreased with increasing strain amplitudes and increased with increasing number of cycles at the high strain amplitudes due to the presence of pseudoelastic behavior. Fatigue parameters following the Coffin-Manson and Basquin’s equations were evaluated. Fatigue crack initiation was observed to occur from the specimen surface and crack propagation was characterized by striation-like features coupled with secondary cracks.
The tensile deformation and fracture behaviour of the aluminium alloy 6061 reinforced with SiC has been investigated. In the T4 temper plastic deformation occurs throughout the gauge length and the extent of SiC particle cracking increases with increasing strain. In the T6 temper strain becomes localised and particle cracking is more concentrated close to the fracture. The elastic modulus decreases with increasing particle damage and this allows a damage parameter to be identified. The fraction of SiC particles which fracture is less than 5%, and over most of the strain range the damage controlling the tensile ductility can be recovered, indicating that other factors, in addition to particle cracking are important in influencing tensile ductility. It is suggested that macroscopic fracture is initiated by the SiC particle clusters that are present in these composites as a result of the processing. The matrix within the clusters is subjected to high levels of triaxial stress due to elastic misfit and the constraints exerted on the matrix by the surrounding particles. Final fracture is then produced by crack propagation through the matrix between the clusters.
The pickup of impurity Fe is an inherent engineering problem for the recycling of aluminium alloys, due to the detrimental effects of Fe containing intermetallic compounds on the mechanical properties. This work aims to understand the effects of intensive forced melt convection and alloying on the mechanical properties of Fe containing Al–Si based cast alloys. Varied Fe levels were introduced into widely used commercial Al–Si based cast alloys with different Mn contents. The role of intensive forced melt convection was investigated through comparative study of the microstructure properties relationship of alloys that are processed via rheo-diecasting (RDC) and conventional high-pressure diecasting (HPDC), with the former involving intensively shearing the melt in a slurry maker before diecasting. CALPHAD modelling of the thermodynamic properties of the multi-component alloys was carried out to clarify the role of alloying elements on the formation of different primary Fe containing intermetallic compounds. The experimental results show that intensive forced melt convection during solidification promotes the formation of α-AlFeMnSi compound with a compact morphology. It was also found that Mn as an alloying element assists the conversion of needle-shaped β-AlFeSi compound into more compact α-AlFeMnSi compound.
Sand-cast plates of a commercial AZ91C alloy have been used for the study. Varying the solidification rate by placing large cast-iron chills in the mould produced a range of secondary dendrite arm spacing (SDAS) within the cast plates. The plates were solution heat-treated, quenched and aged at 165 °C for up to 350 h. The SDAS (μm) varied with the solidification time, tf (s), as SDAS=5.3 tf0.43. The tensile ductility in the as-quenched (T4) condition did not depend on the solidification rate whilst in the T6 condition it tended to decrease for slowly solidified material (SDAS>50 μm). The yield strength and hardness increased and the ductility decreased with ageing. The fracture mode changed from predominantly transgranular in the T4 condition to predominantly intergranular in the T6 condition. The properties of the sand-castings are compared with those of high-pressure diecastings and the possible strengthening mechanisms are discussed. A number of areas that require more research are pointed out.
Iron is the most common and detrimental impurity in aluminum casting alloys and has long been associated with an increase in casting defects. While the negative effects of iron are clear, the mechanism involved is not fully understood. It is generally believed to be associated with the formation of Fe-rich intermetallic phases. Many factors, including alloy composition, melt superheating, Sr modification, cooling, rate, and oxide bifilms, could play a role. In the present investigation, the interactions between iron and each individual element commonly present in aluminum casting alloys, were investigated using a combination of thermal analysis and interrupted quenching tests. The Fe-rich intermetallic phases were characterized using optical microscope, scanning electron microscope, and electron probe microanalysis (EPMA), and the results were compared with the predictions by Thermocalc. It was found that increasing the iron content changes the precipitation sequence of the beta phase, leading to the precipitation of coarse binary beta platelets at a higher temperature. In contrast, manganese, silicon, and strontium appear to suppress the coarse binary beta platelets, and Mn further promotes the formation of a more compact and less harmful a phase. They are therefore expected to reduce the negative effects of the phase. While reported in the literature, no effect of P on the amount of beta platelets was observed. Finally, attempts are made to correlate the Fe-rich intermetallic phases to the formation of casting defects. The role of the beta phase as a nucleation site for eutectic Si and the role of the oxide bifilms and AIP as a heterogeneous substrate of Fe intermetallics are also discussed.
Banded defects are often found in high-pressure die castings. These bands can contain segregation, porosity, and/or tears, and changing casting conditions and alloy are known to change the position and make-up of the bands. Due to the complex, dynamic nature of the high-pressure die-casting (HPDC) process, it is very difficult to study the effect of individual parameters on band formation. In the work presented here, bands of segregation similar to those found in cold-chamber HPDC aluminum alloys were found in laboratory gravity die castings. Samples were cast with a range of fraction solids from 0 to 0.3 and the effect of die temperature and external solid fraction on segregation bands was investigated. The results are considered with reference to the theological properties of the filling semisolid metal and a formation mechanism for bands is proposed by considering flow past a solidifying immobile wall layer.
The strain dependence of particle cracking in aluminum alloys A356/357 in the T6 temper has been studied in a range of microstructures produced by varying solidification rate and Mg content, and by chemical (Sr) modification of the eutectic silicon. The damage accumulates linearly with the applied strain for all microstructures, but the rate depends on the secondary dendrite arm spacing and modification state. Large and elongated eutectic silicon particles in the unmodified alloys and large pi-phase (Al9FeMg3Si5) particles in alloy A357 show the greatest tendency to cracking. In alloy A356, cracking of eutectic silicon particles dominates the accumulation of damage while cracking of Fe-rich particles is relatively unimportant. However, in alloy A357, especially with Sr modification, cracking of the large pi-phase intermetallics accounts for the majority of damage at low and intermediate strains but becomes comparable with silicon particle cracking at large strains. Fracture occurs when the volume fraction of cracked particles (eutectic silicon and Fe-rich intermetallics combined) approximates 45 pct of the total particle volume fraction or when the number fraction of cracked particles is about 20 pct. The results are discussed in terms of Weibull statistics and existing models for dispersion hardening.
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