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Industrial development of gas induced semi-solid process

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Abstract

The gas induced semi-solid (GISS) is a rheocasting process that produces semi-solid slurry by applying fine gas bubble injection through a graphite diffuser. The process is developed to be used in the die casting industry. To apply the GISS process with a die casting process, a GISS maker unit is designed and attached to a conventional die casting machine with little modifications. The commercial parts are developed and produced by the GISS die casting process. The GISS die casting shows the feasibility to produce industrial parts with aluminum 7075 and A356 with lower porosity than liquid die casting.

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... On the other hand, this process utilizes the principle of rapid heat extraction and vigorous local extraction using the injection of fine gas bubbles through a graphite diffuser. Semi-solid slurries with different solid fractions can be obtained simply by varying the diffuser immersion times1011121314. Wannasin et al., studied the semi-solid die casting at low solid fraction of about 10% ADC10 alloy using the GISS process. ...
... This may lead to low mechanical properties [15,16].Several forming processes such as die casting, squeeze casting, gravity casting, and rheo-extrusion of the slurries prepared by the GISS process have been investigated and developed for the past two years.Fig. 3 shows schematics of these GISS forming processes [9,10,1213141516. ...
Article
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Gas-induced semi-solid (GISS) technique is a new rheo-casting process that utilises the principle of rapid heat extraction and vigorous local convection using the injection of fine gas bubbles through a graphite diffuser in molten metal. This study presents microstructural evolution of A380 aluminium alloy produced by GISS process. Samples of semi-solid A380 aluminium alloy were taken at different gas injection times in an optimum temperature above liquidus. Microstructural studies revealed that after conducting GISS process, the morphology of primary α-Al changes from coarse dendritic to rosette-like and finally to fine globular. The sphericity of 0.88, particle size of 54.23 μm and number of 177 α-Al particles per mm2 for α-Al phase were achieved using GISS technique under optimum condition. The results showed the well distribution of α-Al phases in the microstructure of the alloy produced by GISS process. Also the impact strength of A380 alloy was increased with employing GISS process, and more ductility of A380 alloy was achieved.
... Curle [57] also found the porosity in 6082-T6 and 7075-T6 samples caused by incipient melting during solution heat treatment have a negative effect on the elongation, suggesting that optimizing or redesigning the solution heat treatment procedure after determining the melting points of precipitated phase may be beneficial to improve the brittleness. Recent studies on 7050 alloy [100] confirmed their statement and the author proposed that further controlling impurity contents in the alloy would be profitable to the elongation and strength as the eutectic Si and Al7Cu2Fe phases still Comparation of tensile behaviors of some wrought Al alloys and A356 alloy fabricated by conventional casting and rheoforming in the as-fabricated and heat-treated condition [56,57,69,70,73,78,79,91,95,[102][103][104][105][106][107][108][109][110]. ...
... Comparation of tensile behaviors of some wrought Al alloys and A356 alloy fabricated by conventional casting and rheoforming in the as-fabricated and heat-treated condition[56,57,69,70,73,78,79,91,95,[102][103][104][105][106][107][108][109][110]. ...
Article
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Semi-solid processing (SSP), including rheoforming and thixoforming, offers a promising opportunity to manufacture net-shaped parts with complex structure and excellent mechanical properties. Owing to its low cost and short process, rheoforming has been the subject of extensive study over the last two decades. The interest in the rheoforming of wrought aluminum alloys is progressively growing among both the research and industrial communities. This review starts with reviewing the recent efforts and advances on preparation of semi-solid slurry of wrought Al alloys, followed by discussing the correlation between microstructure and performance of these alloys. Finally, special attention is paid in the industrial application and the future trends of rheoforming of wrought aluminum alloys.
... Gas induced semisolid (GISS) process was invented by Wangnasin et al. [68][69][70][71][72] at Prince of Songkla University, and the device is schematically shown in Fig. 4. In the metal slurry preparation process, Ar gas is introduced into the superheated alloy melt as a stirring agent, and then the melt is continuously stirred during the continuous cooling process. After reaching the predetermined temperature, the Ar gas nozzle is taken out and the semisolid slurry with a certain solid fraction is obtained. ...
... After reaching the predetermined temperature, the Ar gas nozzle is taken out and the semisolid slurry with a certain solid fraction is obtained. Although this technology has shown a good commercial application prospect in the preparation of Al alloy slurry because of its simple process and relative low cost [68][69][70], according to the experimental work by Zhang et al. [73][74][75], the method presents a great application potential in the preparation of Mg alloy slurry as well. ...
Article
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A reflection upon the recent developments of semisolid rheoforming techniques of magnesium (Mg) alloys is vital for successfully shaping the future landscape of lightweight and high-performance metal materials. In our paper, formation mechanisms of non-dendritic structure were firstly reviewed, and slurry preparation methods as well as rheoforming processes of Mg alloys were then summarized. Afterwards, microstructures and mechanical properties of semisolid Mg alloys were elaborated. The various formation mechanisms of non-dendritic structures provide theoretical bases for understanding the microstructure evolution of semisolid metal slurries. Despite the abundant slurry preparation methods to date, inexpensive industrial solutions for producing high-quality Mg alloy slurries are still scarce, which is constituting one of many key challenges in the future. In the case of rheoforming processes, high pressure die casting (HPDC) and squeeze casting are the most promising processes for mass production of semisolid Mg alloys. At present, researches on semisolid Mg alloys are mainly focused on AZ and AM series alloys. To develop high-performance semisolid Mg alloys, the slurry preparation and rheoforming technologies of Mg-RE alloys are worthy of further investigation.
... From material processing solutions perspective, such methods are often timeconsuming, complex and very hard to control the process. New approaches in slurry fabrication technology, such as Semi-Solid Rheocasting (SSR) [16], the Gas-Induced Semi-Solid (GISS) [17] and RheoMetal TM processes [18] apply shear forces when nucleation starts by means of an internal heat absorber (inserting a cold part into the melt). This novel approach decreases the time for slurry formation and achieves almost the same production time as the conventional HPDC (high-pressure die-casting) method. ...
Thesis
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Semi-Solid Metal (SSM) casting is a promising technology offering an opportunity to manufacture net-shape, complex geometry metal components in a single operation. However, the absence of foundry guidelines and limited design data for SSM casting makes it challenging to predict the performance of both process and components. The objective of this research was to develop and offer new solutions to material processing-related issues in the electronics industry. By investigating the opportunities afforded by the recently developed RheoMetalTM rheocasting process, a better understanding of the critical factors needed for an effective manufacturing process and optimised component characteristics was achieved. A study of the evolution of microstructure at different stages of the RheoMetalTM process demonstrated the influence of multistage solidification on the microstructural characteristics of the rheocast components. The microstructure of a slurry consists of the solute-lean and coarse globular α-Al particles with a uniform distribution of alloying elements, suspended in the liquid matrix. Additional solute-rich α-Al particles were identified as being a consequence of discrete nucleation events taking place after the initial slurry production. In the final components, macrosegregation was observed in the form of variations in the ratio of solute-lean coarse globular α-Al particles and solute-rich fine α-Al particles in both longitudinal and transverse directions. The relation between microstructural characteristics and material properties was established by determination of the local properties of a rheocast component. The fracture of a rheocast telecom component was strongly affected by microstructural inhomogeneity. In particular, macrosegregation in the form of liquid surface segregation bands and sub-surface pore bands strongly affected the fracture behaviour. Thermal conductivity measurements revealed that regions of the component with a high amount of solute-lean globular α-Al particles showed higher thermal conductivity. The effect of the local variation in thermal conductivity on the thermal performance of a large rheocast heatsink was evaluated by simulation. The results clearly show the importance of considering material inhomogeneity when creating a robust component design.
... The Al-Zn-Mg-Cu alloys with high strength and toughness are widely used in the aerospace industry and are usually manufactured by wrought technique which is more expensive than the traditional casting methods [1,2]. However, Al-Zn-Mg-Cu alloys prepared by conventional casting methods are prone to form casting defects such as hot tearing and shrinkage porosity which will make the tensile properties worse [3,4]. The semisolid metal forming technology has many advantages and can directly cast Al-Zn-Mg-Cu wrought aluminum alloys [5,6]. ...
Article
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The microstructure and mechanical properties of semisolid rheo-diecasting Al-xZn-2Mg-1.5Cu alloys with different Zn contents were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness testing (HV) and room temperature tensile testing. Results show that the as-cast microstructure mainly consists of spherical α-Al and Mg(Al, Cu, Zn)2 phases. Furthermore, a small amounts of Al7Cu2Fe phases were also detected along the grain boundary. Increasing the Zn contents from 8–12%, the volume fraction of the Mg(Al, Cu, Zn)2 phases increases from 4.9–7.4%. After solution heat treatment at 470 °C for 8 h, most of the Mg(Al, Cu, Zn)2 dissolves into the α-Al matrix, while the Al7Cu2Fe phase keeps with remains. The yield strength linearly increases from 482 ± 5 MPa of 8% Zn to 529 ± 5 MPa of 12% Zn. While, the ultimate strength of 10% Zn is 584 ± 2 MPa, which is higher than that of the other two alloys. Moreover, the average elongation dramatically decreases from 13% for the 8% Zn alloy to 2% for the 12% Zn alloy.
... As can be seen in S/N ratio plot given in Fig. 4, the optimum condition is A 3 B 3 C 2 D 1 . Effect of gas blowing time has an increasing trend on pro-cess, which supports the Wannasin et al. study on porosity reduction [14]. On the other hand, extreme gas blowing time affects the melt's characteristics negatively. ...
Chapter
High pressure die casting (HPDC) is an essential method for automotive, aviation and white good industry. Low cycle time due to fast solidification enables mass production. However, porosity and shrinkage are main failures that decreases efficiency. To prevent this, one of the solution is partial-solid casting. Casting in semi-solid phase affects the fluidity of the molten alloy and die filling. Dendritic microstructure turns into globular microstructure and it provides increase in yield and tensile strength, hardness and elongation at break. In this study, the factors affect the porosity ratio were determined as melt temperature, gas blowing time for producing partial-solid slurry, second phase velocity and gate thickness. L9 Taguchi method is used for process design and optimization of high pressure aluminum die casting. As responses porosity level and microstructural changes were determined. Microstructural, morphological and nondestructive testing were used in characterization. “A” class quality partial-solid aluminum automotive parts are successfully produced by Taguchi optimization.
... The main difficulty of the application of the 7075 aluminum alloy in rheocasting is its high sensitivity of the solid fraction to temperature, which leads to difficult to control solid fraction and the uniform of solid fraction in slurry. So far, although many semi-solid slurry making technologies of the 7075 aluminum alloy, such as gas induced semi-solid process (GISS) [7], Council for Scientific and Industrial Research Rheo Casting System (CSIR-RCS) [8], inverted cone-shaped pouring channel process (ICSPC) [9] and forced convection rheoforming process (FCR) [10], have been proposed there has been little study on controlling temperature in semi-solid slurry. In order to reduce the temperature difference in semi-solid slurry, the enthalpy compensation process, in which the core was electromagnetic heating in the outside of the metallic crucible containing aluminum alloy melt, has been proposed in this research. ...
Article
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Rheocasting processes have several technological advantages, such as shorter processing and lower cost than thixocasting processed, while better product quality than conventional die casting. At present, the common alloys used in rheocasting processes are mainly Al-Si alloys which have limited strength. There is a strong demand for higher strength aluminum alloys in industries, for instance the 7075 aluminum alloy. However, the solid fraction of the 7075 aluminum alloy varies significantly with the temperature change in the medium solid fraction range from 0.4 to 0.6, which poses a great challenge to the slurry preparation. The enthalpy compensation process, in which the core was electromagnetic heating in the outside of the metallic crucible containing aluminum alloy melt, has been proposed to reduce the temperature difference within semi-solid slurry in this work. This study used simulation method to analyze the effects of key process parameters on the temperature difference within the 7075 aluminum alloy slurry. The simulation results indicated that semi-solid slurry with medium solid fraction may be obtained and temperature difference may be reduced to less than 4°C.
... High strength 7075 Aluminium alloy is commonly wrought to a formed product, which in practice means high production costs and many steps in the production process. In contrast, the Gas Induced semi-solid (GISS) is a superheated slurry casting process, which has been developed to form the 7075 Aluminium alloy with uniform microstructure and high quality [1][2][3]. Heat treatment of GISS cast 7075 Al alloy has been investigated [2], and it was found that the cast alloy had strength close to those of thixoformed products. Although the cast alloy strength still has not met the target for wrought alloys, in creep properties the cast alloys have surpassed the wrought alloys. ...
... In recent years, rheological HPDC (Rheo-HPDC) technology has acquired increasing attention as an effective process for improving the microstructure and properties of aluminum alloys [9][10][11]. Rheo-HPDC provides components with many advantages, such as low porosity, high mechanical properties, good corrosion resistance, and heat treatability [10][11][12][13]. Segregation exists extensively in components formed by molding technologies [14], such as gravity casting [15], HPDC [16], forging [17], and extrusion [18]. ...
Article
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The segregation behavior of a rheological high pressure die-casting (Rheo-HPDC) AC46000 aluminum alloy at positions with different wall thicknesses was studied. The results reveal that positions with different wall thicknesses exhibit different cooling rates that can result in distinctly different segregation characteristics. Segregation results in varying microstructure, elemental distribution, and hardness along the thickness of an alloy. The segregation in a Rheo-HPDC AC46000 alloy can be categorized as: cross-sectional segregation along the thickness and center segregation. As the distance from the alloy surface increases, the volume fraction of the primary phase increases, and the hardness of the microstructure and content of the eutectic Al-Si, Al2Cu, and α-(FeMn)3Si2Al15 phases decrease. As the alloy wall thickness increases, the differences in the volume fraction of the primary phase, elemental content, and hardness of the microstructure between the edge and center gradually decrease. Compared with the normal center microstructure, the volume fraction of the primary phase in the center segregation microstructure is lower, and the morphology is not round. The content of the eutectic Al-Si, Al2Cu, α-(FeMn)3Si2Al15, and Si phases is higher, and these phases are nonuniformly distributed. Center segregation is often accompanied by shrinkage cracks. As the alloy wall thickness increases, the center segregation area and crack size increase, and the more hard–brittle α-(FeMn)3Si2Al15 particles accumulate the crack. The hardness of the center segregation structure is higher than that of the normal center structure. With increasing alloy wall thickness, the hardness of the center segregation microstructure first increases and then decreases. Keywords: Rheo-HPDC, Aluminum alloy, Segregation, Wall thickness, Intermetallics
... Semisolid forming is highlighted as an ideal way to fabricate magnesium alloy products because of good flowabil- ity [3,4]. Various methods for semisolid slurry preparation have been developed during the past three decades, such as mechanical stirring [5], magneto-hydro-dynamic (MHD) stirring [6], melt conditioner direct chill casting [7], bubble stirring and so on [8][9][10] . The cooling slope method was proposed several years ago [11][12][13][14], but this method needs further studies to improve its feasibility for application. ...
Article
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A melt treatment with a vibrating cooling slope and a semisolid rolling process to produce an AZ61 alloy strip was proposed. The microstructure formation mechanism and the properties of the AZ61 alloy produced by the proposed process were investigated. Due to the high cooling rate and stirring action caused by the vibration cooling slope, the nucleation rate was greatly improved, which caused the formation of fine spherical or rosette primary grains. During the rolling process, the solid fraction increased from the entrance to the exit of the roll gap, and under the shearing action of the roller, the distribution of solute in the melt was homogenous, and the primary grains grew further. When the casting temperature was 680 °C, a strip with a cross section of 4 mm×160 mm was produced and a homogeneous microstructure was obtained. The ultimate tensile strength of the AZ61 alloy strip produced by the proposed method reached 242 MPa, and the corresponding elongation to failure was 4%, which were better than those achieved in previous similar studies.
... Initially, the alloy with determined chemical composition is melted, then this melted is decreased to a specified temperature after which it is kept at that temperature for a while. The critical step of slurry making comes after, stirring of the slurry is carried out by mechanically [12], magnetically or ultrasonically, gas induced [13] stirring is also optional process which is relatively a new approach. Whatever stirring process is used for the preparation of slurry, the objective is the fragmentation of dendrite arms and formation of globular grain structure effectively as mentioned previously. ...
Thesis
This study aims to understand the effect of the semi-solid melting process parameters such as casting temperature and vibration frequency on the mechanical, thermal and microstructural properties. For this purpose, rheocasting of 7075 aluminum alloys were carried out at various temperatures under different vibration frequencies. Microstructure, thermal and mechanical properties of rheocast 7075 alloys were investigated. Optimum microstructure was achieved as globular grain structure in rheocast 7075 alloy with average grain size below 40 μm with porosity amount less than 1%. The highest UTS and flexural strength values were obtained as 483 MPa and 1020 MPa, respectively for the optimum parameter rheocast 7075 alloy.
... These successful applications have proved again the feasibility of SSP to grapple with the issue of large thickness difference of the thin-walled parts, which was usually regarded as a difficult target for classic casting [50]. Furthermore, the GISS process, one of the global market leaders, has found the broadest range of applications [54,72,75,76]. It is recently reported that GISS has been commercially used in almost all areas, but the dominant field is within the communication and electronics industry [72]. ...
Article
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Following the rapid growth of the automotive and communication industries, components with high quality and low cost are eagerly desired in China. Various technologies have been developed in China to meet the demand, while semi-solid processing (SSP) of alloys and composites is one of the most successfully developed and practically applied technologies. The major SSP applied in China is the rheocasting in terms of the Swirled Enthalpy Equilibration Device (SEED) process. In this review, we start with a brief reviewing some common slurry preparation methods and recent innovations of the SEED process. Subsequently, we describe the general situation and some recent examples of successful development and applications of SSP in China. Lastly, the future directions in SSP of alloys and composites are highlighted in this frontier research field at the end of this review.
... This opened up the potential of attaining very complex geometries (as with casting) while improving the components' mechanical properties. Most of the investigations were focused on low solid fractions and low melting point alloys, where very good results were attained and some processes are actually industrialized [3][4][5]. ...
Article
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The benefits of the novel Near Solidus Forming (NSF) process has shown previously in its ability to produce steel components with comparable as-forged mechanical properties but with a cost reduction of 10–15%. This study further pushes the NSF technology to produce parts that are conventionally difficult to produce via conventional methods. A 2.7 kg 42CrMo4 steel grade component was manufactured into a complex geometry using only a 400t press. Different manufacturing parameters were evaluated to show their influence on the process and final component. A combination of X-ray fluorescence (XRF), optical microscopy and SEM analysis of the microstructure was also conducted revealing the deformation pattern of the material and shedding some light on how the material evolves during the process. The successful forging of these components shows the capability to produce previously deemed difficult geometries, with much a lower specification forging press, in a single deformation
... However, the cost of this production route is very high compared to the alternative casting route. Nevertheless, disadvantages of conventional casting are found in the material structure with existence of casting defects such as pores and shrinkage cavities, including lower strength [6]. Al7075 alloy is a widely used high strength structural material with a tensile strength of 510-530 MPa in peak aging condition (solution annealed at 755 K for 2 h and water quenched to room temperature, followed by aging at 390 K for 24 h and air cooled) [7]. ...
Article
This study was undertaken to investigate the influence of Al–8B master alloy and modified strain-induced melt activation process on the structural characteristics and dry sliding wear behavior of Al–12Zn–3Mg–2.5Cu aluminum alloy. The optimum amount of B containing master alloy for proper grain refining was selected as 3.75 wt.%. The alloy was produced by modified strain-induced melt activation (SIMA) process. Reheating condition to obtain a fine globular microstructure was optimized. The optimum temperature and time in strain-induced melt activation process are 590 °C and 10 min, respectively. T6 heat treatment was applied for all specimens before wear testing. Significant improvements in wear properties were obtained with the addition of grain refiner combined with T6 heat treatment. Dry sliding wear performance of the alloy was examined in normal atmospheric conditions. The experimental results showed that the T6 heat treatment considerably improved the resistance of Al–12Zn–3 Mg–2.5Cu aluminum alloy to the dry sliding wear. The results showed that dry sliding wear performance of globular microstructure specimens was a lower value than that of B-refined specimens without strain-induced melt activation process.
... In particular, semisolid forming is an ideal way to fabricate magnesium alloy products because of good flowability [10][11][12] . Many slurry preparation processes have been developed: mechanical stirring [13], Magneto Hydro Dynamic (MHD) stirring [14], Melt Conditioner Direct Chill casting [15], bubble stirring and so on [16]. The Shearing/Cooling and Rolling (SCR) process was proposed several years ago as an effective semisolid slurry preparation method [12]. ...
Article
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A novel semisolid Continuous Shearing and Rolling (CSR) process for producing a Mg-3Sn-1Mn (wt%) alloy strip is developed, and the microstructure formation mechanism and properties of the Mg-3Sn-1Mn (wt%) alloy processed by this process are investigated. At a casting temperature of 690°C and a roll speed of 0.052 m·s−1, a Mg-3Sn-1Mn (wt%) alloy strip with a cross section size of 4×160 mm was produced by the proposed process. Under strong cooling and shearing actions, eruptive nucleation, direct globular grain growth and dendrite arm breakage took place during the process, which caused formations of fine spherical grains. The grain size and roundness of the Mg-3Sn-1Mn (wt%) alloy strip increased with increasing increments of the casting temperature. In this perspective, roll speed obviously affects grain shape. The ultimate tensile strength and elongation of the Mg-3Sn-1Mn (wt%) alloy strip reached 205.93 MPa and 7.2%.
Article
A self-developed forced convection rheoforming (FCR) machine for the preparation of light alloy semisolid slurry was introduced. The microstructure characteristics of 7075 aluminium alloy semisolid slurry at different stirring speeds prepared by the FCR process were analyzed. The experimental results suggest that with the increase of the stirring speed, the mean grain size of the semisolid decreases and the shape factor as well as the number of primary grains increase. Meanwhile, the preparation process of semisolid slurry was numerically simulated. The flow characteristics of the melt in the device and the effect of the stirring speed on temperature field and solid fraction of the melt were investigated. The simulated results show that during the preparation process of semisolid slurry, there is a complex convection within the FCR device that obviously changes the temperature field distribution and solid fraction of the melt. When the convection intensity increases, the scope of the undercooling gradient of the melt is reduced and temperature distribution is improved.
Article
The semi-solid slurry of AZ91D magnesium alloy was prepared by gas bubbling process. The effect of processing parameters, including gas flow rate, cooling rate and stirring end temperature, on microstructure of AZ91D semi-solid slurry was investigated. With increasing the gas flow rate from 0 to 5 L/min, the average size of primary α-Mg particles decreases from 119.1 to 77.2 μm and the average shape factor increases continuously from 0.1 to 0.596. The formation of non-dendritic primary α-Mg particles during gas bubbling is the result of combined effects of dendrite fragmentation and copious nucleation. With increasing the cooling rate from 3.6 to 14.6 °C/min, the average particle size of primary α-Mg phase decreases from 105.0 to 68.1 μm while the average shape factor peaks at 9.1 °C/min. Both high and low cooling rates can induce dendritic growth of primary α-Mg particles. Changing the stirring end temperature from 590 to 595 °C has little effect on the average size and shape factor of primary α-Mg particles in AZ91D semi-solid slurry. The insensitivity of semi-solid microstructures to the stirring end temperature is attributed to the sufficient quantity of primary particles formed in the melt.
Chapter
High volume fraction silicon carbide particle (SiCp) - aluminum metal matrix composites were fabricated for use in a domestic armor application. A SiC powder mixture, consisting of three different average particle size powders (6.3, 2.2 and 0.68 microns), was designed in order to achieve high packing fractions, on the order of 60 to 70%. Near net shape porous SiC preforms were fabricated by die pressing. The preforms were bisque sintered to give them sufficient strength for infiltration. The bisque sintering was conducted either in air to produce an oxide film or by the conversion of a preceramic polymer polycarbosilane (PCS) under an inert atmosphere. The preforms were infiltrated by squeeze casting using 7075 aluminum in a semi-solid state. The infiltrated preforms were given a T6 heat treatment. Polished cross sections and fracture surfaces were observed using optical and electron microscopy to analyze the microstructure. The infiltrated preforms were found to have low residual porosity. Results on mechanical property evaluation and ballistic performance will be reported.
Article
A sloping semisolid rheorolling process of AZ91 alloy was developed, and the effects of process parameters on microstructure and properties of AZ91 alloy strip prepared by the proposed process were investigated. The grain size and roundness of the strip increase with the increment of casting temperature, and the ultimate tensile strength and elongation of the strip decrease. The primary grain size increases with the increment of roll speed. The grain size of the strip decreases first and then increases with the increment of vibration frequency, and mechanical properties increase first and then decrease. When the casting temperature was between 670 and 690°C, the roll speed was 0·052 m s−1, the vibration frequency was 80 Hz, the amplitude was 0·55 mm and the sloping angle was 45°, the AZ91 alloy strip was produced. The ultimate tensile strength of the strip is 215 MPa, and the elongation is 3·02%.
Article
Aged hardening of semisolid cast A356 Al alloy produced by gas induced semi-solid (GISS) process was studied. It was found that maximum hardness and tensile strength could be achieved from specimens aged at 165 °C for 18 h of which the average maximum hardness, the average ultimate tensile strength and the average percent elongation were 96.4 HRE, 312 MPa and 7.6%, respectively. The higher aging temperature of 195 °C for 3 h led to a slightly lower average tensile strength of 305 MPa together with a higher average elongation of 9.8%. The strain hardening exponent of specimens aged at both sets of conditions was lower than that of the as-cast specimen as well as the as-cast specimen aged at 225 °C for 15 min. The mechanical properties of the alloys in this study were comparable to those of typical thixoformed products. β″ phase was mainly responsible to the strengthening of the peak aged alloy. Elongated precipitates were formed in the specimen after prolonged aging at 195 °C for 16 h. The activation energy for the precipitation hardening process of the alloy derived in this research was 128,717 J/mol.
Article
The creep rupture behavior of semi-solid cast 7075-T6 Al alloy produced by the Gas Induced Semi-Solid (GISS) process was investigated and compared to that of commercial 7075-T651 Al alloy. The semi-solid cast 7075-T6 Al alloy displayed lower minimum creep rate and longer creep rupture time than the commercial 7075-T651 Al alloy. On the basis of their stress exponent, n, values of 6.3, dislocation creep was seemingly the predominant mechanism controlling the creep deformation of both alloys. The creep rupture time of the semi-solid cast 7075-T6 Al alloy was distinctly longer than that of the commercial 7075-T651 Al alloy at stress regimes of 120–140 MPa. This difference was attributed to the lower precipitate coarsening and higher precipitate density in the semi-solid cast alloy. Creep cavities predominately controlled the creep rupture of the semi-solid cast 7075-T6 Al alloy despite the appearance of precipitate coarsening. The commercial 7075-T651 Al alloy creep rupture behavior was controlled by the combination of rapid precipitate coarsening and creep cavities. However, de-cohesion between insoluble particles and the matrix is evidently accelerated with increasing stress to 180 MPa, leading to cavity propagation and resulting in the convergence of creep rupture time in the semi-solid cast 7075-T6 Al alloy to that of the commercial 7075-T651 Al alloy.
Article
Effects of Gas Induce Semi Solid (GISS) on shrinkage porosity of 7075 aluminum alloy were investigated. Initial solid fractions were controlled by rheocasting time at 5, 10 and 15 seconds and 4 and 6 bar of gas pressure. The results showed that the initial solid fractions were increased by increasing rheocasting time and gas pressure. As for the shrinkage, values of the GISS process samples were lower than those of the conventional process samples. In addition, the shrinkage areas of semi solid samples were decreased by increasing the initial solid fractions. The microstructure of semi solid samples was shown to be uniform globular grains along the samples.
Article
A novel semisolid continuous shearing and rolling process for producing Mg–3Sn–1Mn (wt%) alloy strip was proposed, microstructure and properties of Mg–3Sn–1Mn (wt%) alloy strip processed by the proposed process and heat treatment was investigated. For each condition, at least three tensile tests were performed. Under strong cooling and shearing actions caused by the rotating roll and the fixed shoe, eruptive nucleation, direct globular grain growth and dendrite arm breakage took place in the roll-shoe gap, which causes the formation of fine spherical or rosette primary grains. When the casting temperature was 690 °C, and the roll speed was 0.052 m s−1, Mg–3Sn–1Mn (wt%) alloy strip was produced. The microstructures of the strip are mainly composed of fine spherical or rosette grains. After deep rolling, the grains of the strip were elongated, the textures were formed in the deep-rolled strip. The ultimate tensile strength (UTS) of the deep-rolled strip is 276±3 MPa, and the elongation (EL) is 6.3±0.1% in the rolling direction (RD). After solution treatment at 480 °C for 13 h and aging at 300 °C for 12 h, the Mg2Sn phase distributes homogeneously in matrix microstructure and strengthens the mechanical properties, the UTS and EL of the deep-rolled strip reach 305±3.3 MPa and 7.8±0.12% in the RD.
Article
A sloping semisolid rheo-rolling process of Mg–3Sn–1Mn alloy was developed, and the effects of process parameters on the microstructure and mechanical properties of Mg–3Sn–1Mn alloy strip were studied. The results show that the primary grain average diameter of the strip increases with the increase of the roll speed. The primary grain average diameter decreases firstly and then increases with the increase of the vibration frequency, and the tensile strength and elongation of the strip increase firstly and then decrease with the increase of the vibration frequency. The primary grain average diameter increases with the increase of casting temperature, and the tensile strength and elongation of the strip decrease correspondingly. When the casting temperature is 670 °C, the roll speed is 52 mm/s, and the vibration frequency is 60 Hz, Mg–3Sn–1Mn alloy strip with good properties is produced. The mechanical properties of the present product are higher than those of Mg–3Sn–1Mn alloy casting with the addition of 0.87% Ce (mass fraction).
Article
Tensile properties of rheo-cast 7075-T6 Al alloy produced by Gas Induced Semi-Solid (GISS) technique was investigated as a function of temperatures from 25°C to 250 °C in order to assess the potent of high temperature applications. It was found that the ultimate tensile strength and yield strength of the alloy decreased steadily with increasing temperature. There was loss in strength of about 33% at 200°C and 46% at 250 °C comparing to the strength at room temperature. At T = 250 °C, the ultimate tensile strength and yield strength of the rheo-cast 7075-T6 Al alloy were higher than those of the wrought 7075-T651 Al alloy. Keyword: 7075 Al alloy; Gas Induced Semi Solid (GISS) technique; Elevated temperature tensile.
Article
Effect of the two-step solution heat treatment on the microstructure of semisolid cast 7075 aluminium alloy has been studied. The microstructure of the as-cast specimens mainly consisted of matrix-α (Al) and grain boundary (GB)-eutectic phase (α-Al + Mg(Zn,Cu,Al)2). After solution treating, coarse black particles were found to form in the single-step solution treated specimens at the condition of 450 °C for 8 h and 480 °C for 1 h, respectively. Two-step solution heat treatment resulted in the reduction of coarse black particle formation while maintaining the same amount of eutectic MgZn2 phase dissolution as the high temperature single-step solution treatment. Therefore, the two-step solution heat treatment enables alloying elements dissolved into the matrix without overheating and hence decreases coarse black particles. The optimum two-step solution heat treatment condition derived from this study was 400 °C for 8 h + 450 °C for 4 h.
Article
Rheo-squeeze casting combined with gas bubbling process was proved effective to improve the mechanical properties of AZ91-2 wt%Ca (AZX912) alloy. Increase of gas flow led to improvement of the quality of AZX912 semi-solid slurry and improved ductility of rheo-squeeze casting AZX912 alloy samples. Increase of applied pressure brought refinement in as-cast microstructure and reduction of porosity, as well as continuous improvement in both tensile strength and elongation. Heat treatment at 410 °C promoted dissolution of β-Mg17Al12 phase, morphology modification of Al2Ca phase and further increase of both tensile strength and ductility. Compared with conventional squeeze casting, the mechanical properties of rheo-squeeze casting AZX912 alloy were improved by more than 20%. The improvement in mechanical properties was mainly attributed to the grain refinement in microstructure.
Article
In this study, a macro-nanocomposite of Al–Al/(SiO2)np was synthesized using powder-in-tube method. Pure aluminum cylinders were cast and then machined to prepare tubes. Nanocomposite powders of Al/(SiO2)np were prepared by mixing 1 and 2 wt% SiO2 nano-particle with aluminum. Then macro-nanocomposites were prepared by compaction of the nanocomposites inside the tubes. The effects of reinforcement weight fraction, volume fraction of nanocomposite in the macro-nanocomposites and hot extrusion on the microstructure and mechanical properties were investigated. Scanning electron microscope (SEM) and optical microscope (OM) were used for microstructural examinations. Mechanical properties were investigated using tensile and compression tests at room temperature. The results revealed that when 25 vol% of the powder-in-tube composite was the nanocomposite reinforced with 2 wt% of nano-particle, the tensile strength was increased by 10.8%. Tensile strength was improved by up to 24% when 64 vol% of nanocomposite reinforced with 1 wt% of nano-particle was employed. Additionally, significant increase in compressive strength was achieved. This is noteworthy that coupling of a pure aluminum sheath with the nanocomposite enhanced the strength with limited loss of ductility. Micrographs showed integrated composites in which the interface between the sheath and the core had no defects.
Article
Four Al-Si-Mg-Fe alloys with Si contents varying from 1.6 to 4.5 wt pct were rheocast, using the RheoMetal™ process to prepare slurry and cast in a vertical high-pressure die casting machine. Particle size and Si concentration in the α-Al particles in the slurry and in the as-rheocast component were investigated. A uniform distribution of Si in the globular α 1-Al particles was achieved in the slurry. In the rheocast samples, measurement of the α 1-Al particles showed that these particles did not increase significantly in size during pouring and secondary solidification. The two additional α-Al particles types, α 2-Al particles and α 3-Al particles, were identified as being a result of two discrete nucleation events taking place after slurry production. The Si concentration in the α 2-Al and α 3-Al particles indicated that the larger α 2-Al particles precipitated before the α 3-Al particles. In addition, in the as-rheocast condition, the Si distribution inside the α 1-Al particles showed three distinct zones; an unaffected zone, a transition zone, and in some cases the start of a dendritic/cellular zone. The phenomenon of dendritic growth of globular α 1-Al particles during secondary solidification occurred concomitantly with the final eutectic reaction and increased with increasing amount of the Al-Si eutectic phase.
Article
The current paper emphasizes various aspects of squeeze casting in the field of metal matrix composites (MMC’s). The effect of different aspects and processing parameters related to squeeze casting such as pressure, slurry temperature, types and effects of reinforcements have been discussed with specific stress on aluminum MMC’s. The development of different mechanical, tribological and wear properties due to squeezing casting have been discussed.
Article
The purpose of this research was to study the diffuse element and mechanical property of Semi-solid casting (SSC) 7075 and 6061 Al alloy from diffusion welding (DW). The results found that Zn elements were successfully diffused. Mg 2 Si and MgZn 2 intermetallics were precipitated from plate-like shape to flake shape. The high bonding temperature and bonding time caused diffuse elements distributed throughout the material. The mechanical property showed that the maximium average tensile strength was 76.80 MPa from bonding temperature at 723 K and 120 min bonding time. The hardness in bonded line was around 63 HV to74 HV.
Article
An efficient and low-cost aluminum alloy uniform solidification control technology, namely, air-cooled stirring rod (ACSR) process, has been developed for preparing large volume semisolid slurry. The semisolid slurry preparation process is connected with the die-casting machine to form multiple integrated intelligent rheological die-casting production lines for the efficient preparation of rheological die-casting of large-scale thin-walled aluminum alloys. At present, the ACSR process can produce 40 kg of large-volume semisolid slurry with a solid phase ratio of 25% to 35% within 30 s. This rheological die-casting process has been industrialized for the preparation of high-quality aluminum alloy large-scale thin-walled parts, such as new energy vehicles and 5G communications. Typical products produced by this process include heat dissipation housings for 5G communications, filter housings, antenna chassis and three-electric structural shell, end cover, and ABS system valve body for new energy vehicles. Compared with traditional die castings, aluminum alloy castings prepared by the new process not only have fine and spherical microstructures, good surface quality, and fewer internal pores but also enjoys more excellent mechanical properties and thermal conductivity.
Article
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Owing to its low cost, short process and low energy consumption, semi-solid processing (SSP) of aluminum (Al) and magnesium (Mg) alloys has been considered as a competitive approach to fabricate complicated components with excellent performance. Over the past decade, significant progress has been achieved in deeply understanding the SSP process, the microstructure and performance of the fabricated components in China. This paper starts with a retrospective overview of some common slurry preparation methods, followed by presenting the performance and the underlying mechanisms of SSP fabricated alloys. Then, the mainstream opinions on the microstructure evolution and rheological flow behavior of semi-solid slurry are discussed. Subsequently, the general situation and some recent examples of industrial applications of SSP are presented. Finally, special attention is paid to the unresolved issues and the future directions in SSP of Al and Mg alloys in China.
Article
A new technique for preparing semisolid slurry, namely, distributary-confluence runner (DCR), was combined with die-casting (DC) to conduct rheological die-casting (R-DC) of A356 alloy. The mechanism of DCR for semisolid slurry preparation was determined via numerical simulations and experiments. The microstructure and mechanical properties of A356 alloys prepared via DC and R-DC were studied. High-quality slurry containing numerous primary α-Al (α1-Al) with an average size of 49 μm and a shape factor of 0.81 could be prepared via DCR. Simulation results indicated that the unique flow state and physical field changes during slurry preparation were conducive to accelerating the uniformity of melt temperature and composition fields, nucleation exfoliation, and spherical growth. Compared with the alloy prepared via DC, the tensile strength, yield strength, and elongation of A356 alloy prepared via R-DC increased by 19%, 15%, and 107%, respectively.
Article
A simple and efficient semisolid slurry preparation technique, called distributary-confluence channel (DCC), was developed to prepare high-quality semisolid slurries of aluminum and magnesium alloys. The DCC process was coupled with the use of a high pressure die-casting (HPDC) machine to successfully achieve near-net forming and implement production applications with rheological high pressure die-casting (Rheo-HPDC) for various Al and Mg alloy castings. The changes in the flow state and in the physical field of the melt during the slurry preparation via the DCC technique were investigated by numerical simulations. The nucleation mechanism and the growth law of the primary grain during the DCC process were discussed. The microstructures, porosities, and mechanical properties of the aluminum and magnesium alloys prepared via DCC Rheo-HPDC were studied. The results show that semisolid slurries containing a large amount of primary grains with an average size < 50 μm, a shape factor > 0.8, and uniformly dispersed in the liquid matrix can be prepared via DCC. The simulation results indicate that the melt exhibits opposite velocity vectors on the upper part and on the lower part of the DCC. Moreover, it encounters and collides at the confluence to generate convection, which is beneficial to obtain uniform melt temperature, composition fields, nuclei exfoliation, and spherical growth. The random particle tracking simulation results show that the DCC process improves the composition field of the slurry. The DCC process facilitates the melt nucleation by using multi-channel chilling and increasing the nucleation area. The self-stirring generated during the flow of the melt produces a large amount of free nuclei inside the melt. There exist two main mechanisms behind the formation of the spherical primary grains. The one is the mechanism of explosive nucleation and spheroidal growth, the other is the dendrite arm necking, fusing, grain ripening, and rounding. Furthermore, by comparing identical alloy castings produced via traditional HPDC and other Rheo-HPDC processes, the DCC Rheo-HPDC castings present finer and rounder grains, a lower porosity, and more performant mechanical properties.
Article
An air-cooled stirring rod (ACSR) process for efficiently preparing large volumes of semisolid slurry was introduced. A new low-cost casting Al–Si–Fe–Mg–Sr alloy was used to prepare large thin-walled heat-dissipating shells using both conventional HPDC and ACSR rheological high pressure die-casting (Rheo-HPDC) technologies. Their microstructures, thermal conductivities, elevated temperature and room temperature mechanical properties, and corrosion behaviors were compared. Furthermore, this work analyzed the mechanisms responsible for the microstructure refinement and performance enhancement in ACSR Rheo-HPDC alloys. The results showed that only 25 s was needed to prepare 32 kg of the semisolid slurry using ACSR process. The alloy prepared by ACSR Rheo-HPDC generated a large number of fine spherical primary α-Al particles with a volume fraction greater than 40%. The Rheo-HPDC alloy showed a moderate strength, high plasticity, and high heat conductivity. The heat conductivity, ultimate tensile strength and elongation of the Rheo-HPDC alloy were 184 W/(m.K), 264 MPa and 12.2% respectively, while those of the HPDC alloy were 167 W/(m.K), 228 MPa and 5.8% respectively. The improvement of heat conductivity of the alloy formed via ACSR Rheo-HPDC was mainly ascribed to the decrease of electron scattering by the refinement of eutectic silicons and Fe-rich intermetallics. This allowed the electron flow to pass through the eutectic Si region more easily. The refined and uniformly-distributed heat-resistant β-Al5FeSi intermetallics effectively prevented grain boundary sliding, so the Rheo-HPDC alloy showed superior high-temperature mechanical properties. The Rheo-HPDC alloy presented a more excellent corrosion resistance to the conventional HPDC alloy due to the refinement of iron-rich phase and eutectic silicons and the reduction in the potential difference between the matrix and the iron-rich phase.
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از جنبه ی تاریخی، شکل دهی فلزات همیشه نگرانی عمده ی بشر در تلاش برای بدست آوردن انواع مختلف اشیاء مانند اسلحه و ابزار بوده است. روش های مختلفی برای شکل دهی فلز توسعه یافته است که بطور کلی در دو دسته ی ریخته گری و آهنگری خلاصه می شوند. در فرآیند ریخته گری، ابتدا آلیاژ تا نقطه ذوب گرم می شود و سپس آلیاژ مایع داخل قالبی با شکل دلخواه ریخته می شود. عمده مصرف انرژی در این فرآیند مربوط به گرماش فلز است. فرآیند ریخته گری قابلیت تولید قطعات با اشکال هندسی پیچیده و اجزای جداره نازک برای تولید قطعات سبک را داراست اما انقباض ناشی از انجماد منجر به تخلخل و تضعیف خواص مکانیکی محصول نهایی می شود. از روش های مرسوم برای تولید قطعات جداره نازک و قطعات با هندسه پیچیده، استفاده از فرآیند ریخته گری تحت فشار است اما به دلیل سرعت بالای حرکت فلز مایع در سیستم راهگاهی و محفظه قالب، مذاب دچار اغتشاش و تلاطم شدیدی می شود که این امر منجر به پاره شدن فیلم اکسیدی و ورود آن به مذاب و همچنین به دام افتادن هوا در قطعه نهایی می شود و وجود عیوب مذکور باعث افت شدید خواص مکانیکی در قطعه نهایی می گردد. در فرآیند آهنگری، آلیاژ در حالت جامد شکل داده می شود و بیشترین مقادیر انرژی در ایجاد بار لازم برای شکل‌دهی فلز صرف می شود. این فرآیند قادر به ایجاد قطعات با خواص مکانیکی بسیار خوب است اما به تولید قطعات با هندسه ساده تر از ریخته-گری محدود می شود و ضایعات مواد در آن نسبت به ریخته گری بیشتر است. فرآیند فلز نیمه‌جامد، فرآیندی میانی است و بر رفتار ویژه ی دوغاب نیمه‌جامد تکیه دارد. این مواد رفتار تیکسوتراپی از خود نشان می دهند که با بروز رفتار "جامد مانند" در حالت استراحت و رفتار "مایع مانند" در حالت جریان شناخته می شوند. شکل دهی نیمه‌جامد فلزات یک فناوری جذاب است که امکان تولید اجزا و قطعات با هندسه ی پیچیده و نزدیک به شکل نهایی را در یک گام فراهم می کند و بطور همزمان خواص مکانیکی بالایی نیز می تواند به علت رفتار جریانی و ریزساختار منحصر به فرد آلیاژ حاصل شود. متأسفانه با وجود گذشت بیش از چهل سال از ابداع فرآیند فلز نیمه‌جامد، تحقیق، توسعه و بکارگیری گسترده آن در صنایع خودروسازی، هوافضا ، الکترونیک و همچنین انتشار تعداد بسیار زیادی مقاله در این زمینه، تعداد اندکی کتاب لاتین منتشر شده است که هیچکدام بطور جامع و بنیادی به موضوع نپرداخته اند. در کشور عزیزمان ایران نیز عدم وجود منبعی منسجم و یکپارچه در این زمینه بشدت احساس می شد. بنابراین بر آن شدیم تا با تألیف کتاب پیش رو، مقداری هر چند اندک از دین خود به سیستم آموزشی و جامعه مهندسی کشور را ادا کنیم. کتاب حاضر، حاوی مطالب بنیادی و ضروری جهت کسب دانش در زمینه فرآیند فلز نیمه‌جامد، شامل مکانیزم های تشکیل ساختار نیمه‌جامد، روش های اندازه گیری کسر جامد دوغاب، رئولوژی و رفتار سیلانی دوغاب، روش های تولید و شکل دهی مواد اولیه با ساختار غیر دندریتی و کامپوکستینگ است. با وجود گستردگی، پراکندگی و عدم جامعیت منابع لاتین موجود، مطالعه ی این کتاب، کمک شایانی به دانشجویان برای ورود و درک هرچه بهتر فرآیند فلز نیمه‌جامد بوده و همچنین برای مهندسان ریخته گری خالی از فایده نخواهد بود.
Article
A low-cost, new casting Sr-modified Al-7.5Si-0.8Fe alloy with high-thermal conductivity was prepared into large thin-wall heat-dissipating shells for 5G communication base stations using a traditional high pressure die-casting (HPDC) process and a rheological HPDC (R-HPDC) technique. Their microstructure, tensile property, hardness, thermal conductivity, and corrosion behavior were analyzed. The R-HPDC Al-7.5Si-0.8Fe alloy shows a refined microstructure in terms of α1-Al particles, α2-Al grains, fibrous β-Al5FeSi, and granular eutectic silicons when compared to traditional HPDC alloys. The R-HPDC alloy has a thermal conductivity, elongation-to-failure value, ultimate tensile strength, yield strength, and Vickers hardness of 186 W/(m.K), 12.4 %, 235 MPa, 114 MPa, and 70 HV, respectively. These values are respectively 6 %, 91 %, 22 %, 14 %, and 11 % higher than those reported for conventional HPDC alloys. Moreover, the R-HPDC Al-Si-Fe alloy shows a superior corrosion resistance in comparison to HPDC alloys. This observation is supported by scanning Kelvin probe (SKP) measurements and electrochemical tests. The improved performances arise mostly from the refinement of the iron-rich intermetallics (β-Al5FeSi) and eutectic silicons, the increase in the area proportion of α2-Al grains relative to eutectic silicon, and the reduction in the potential difference between the aluminum matrices and the iron-rich intermetallics.
Conference Paper
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Achieving high efficiency in the high pressure die casting technique is possible with improving production efficiency and reducing energy costs as all other production methods. Pressure die casting alloys are made of high-silicon and high-fluidity alloys and the quality problems of the products produced by this technique, are shrinkage and porosity in in cast structure. The viscosity of molten metal is reduced by the partial-solid casting method to be applied in the pressure die casting technique, thus making it easier to fill the mold by increasing the fluidity. Increase in mold filling.makes it possible to obtain a higher quality product by reducing porosity ratio. Moreover, an advantage of partial-solid casting; dendritic structure is prevented and a structure in globular grain form is obtained. The low porosity ratio and the spherical grain structure improve the toughness of the material thereby increasing the strength values of the material. In this study; EN AC 43400 (AlSi10Mg (Fe)) aluminum alloys are produced with GISS (Gas Induced Semi-Solid) method and high pressure casting technique (HPDC). GISS method and possitive effects in casting temperature as well as alloy hardness, yield-tensile strength, elongation and microstructure.were observed.
Article
The anodizing parameters of voltage, current density, temperature, and electrolyte choice were assessed to find an appropriate combination for the superheated slurry cast 7075 Al alloy substrate. The alloy was anodized in sulfuric acid electrolyte or alternatively in sulfuric acid mixed with boric acid or citric acid. The voltages applied were in the range of 15−30 V. Anodizing current densities tested were 2 and 3 A/dm², while temperatures tested were 5 and 15 °C. Thickness, surface morphology, hardness, and corrosion resistance of the oxide film were then evaluated. It was found that 25 V, 2 A/dm² and 5 °C were suitable for this alloy when anodized in sulfuric acid. The oxide film was smooth with uniform thickness, low porosity, high hardness, and had the highest corrosion resistance at these parameters. However, discontinuous oxide films were observed from samples anodized at higher temperature of 15 °C. Alternative electrolytes considered were sulfuric acid mixed with boric acid or citric acid. The results showed that electrolytes with boric acid or citric acid increased thickness, hardness, corrosion resistance and quality of the oxide films. However, these oxide films were inferior to those obtained with sulfuric acid electrolyte at lower temperature (25 V, 2 A/dm² and 5 °C).
Article
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In this study, there are three machining parameters consist of spindle speed, feed rate and depth of cut which were conducted through full factorial with four center points to determine the effect of machining parameters on the surface roughness and verify whether there is curvature in the model for CNC face milling process in an automotive components manufacturer in Thailand. The workpieces used semi-solid die casted ADC12 aluminum alloy crankcase housing which they were performed by the ARES SEIKI model R5630 3-axis CNC vertical machining center and face milling cutter with diameter of 63 millimeters. The surface roughness of face-milled was measured by the surface roughness tester. It was found that the greatest main effect influence to surface roughness was spindle speed, followed by feed rate and depth of cut at significance level of 0.05.
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Below-knee prosthesis is much needed in Thailand and the world over because it serves as a close substitute for a missing body part (e.g. a device to aid people with paraplegia). Production of these components by gas-induced semi-solid process is relatively new, and investors need to be assured of success before committing themselves into a venture. Most cost models, such as the activity-based model, have flexibility limitations, and hence more input-sensitive – the process-based cost model (PBCM) – is alternatively employed in analysing more simple work process, appropriate production volume and unit cost, and was utilised in this research. An array of production volumes (5000–100,000 sets) and a number of daily work shifts (1–3) were investigated. From detailed breakdowns, analysis results suggested an optimal annual production volume in the range of 10,000–40,000 sets employing any shifts per day. Below 10,000, unit cost escalates very sharply, and beyond 40,000 it decreases only marginally. Production for export purposes is feasible since the annual domestic requirement in Thailand is only a fraction of this volume. PBCM had also proven an effective tool in this case.
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Semi-solid metal processing technologies have been intensively studied in recent years. Gas Induced Semi-Solid (GISS) is a slurry preparation technique for producing non-dendritic or globular structures for cast alloys. In the present study, GISS technique was used in conjunction with conventional die cast process for casting Al–Si–Mg–Fe alloy. The shape of die cast specimen was designed as a simple flat plate. The variation of microstructures and tensile properties of specimens from different locations of cast plates was studied. The results show that the specimens from bottom location, near the gate section and the middle location of cast plates are stronger and more ductility than those from the top location. The microstructural examination reveals that the specimens from top location of cast plates contain more defects, such as shrinkage pores than those from the other locations. These defects are resulted in lower strength and ductility of the cast product.
Article
In present study, the semi-solid slurry of the AZ91-2Ca-1.5Ce alloy was firstly prepared by gas-bubbling processing and then was formed by die casting and squeeze casting, respectively. The influence of processing parameters on microstructure and mechanical properties of the alloy was investigated. The results show that increase of gas-flow rate and appropriate pouring temperature can improve the quality of the semi-solid slurry and change the morphology of primary α-Mg particles to rosette-like shape or roundness. Meanwhile, the addition of calcium and cerium refines the as-cast microstructure and dramatically improves the tensile properties, also the strengthening phase Al4Ce exists around the grain boundary. The peak ultimate tensile strength (UTS), yield strength, and elongation of rheo-die casting AZ91-2Ca-1.5Ce alloy are 202 MPa, 154 MPa, and 2.3%, respectively. Especially, compared with conventional liquid die-casting, the UTS and elongation of rheo-die casting AZ91-2Ca-1.5Ce alloy were improved by 8% and 64%, respectively. Meanwhile, the rheo-die casting alloy also showed higher mechanical properties than rheo-squeeze casting alloy, since the higher speed that die casting provided could induce more compact microstructure and remain the semi-solid characteristic better.
Article
Effects of solution heat treatment and age hardening on the microstructures and mechanical properties of rheocasting 7075 Al alloy produced by a novel technique, Gas Induced Semi-Solid (GISS) technique, were studied. This work reveals that the optimum solution heat treatment condition for the non-dendritic structured 7075 aluminium alloy was 450°C for 4h. Age hardening was performed at temperatures of 120°C, 145°C, 165°C, and 185°C under various time durations. The peak aging condition was the artificial aging at 120°C for 72h, at which a highest tensile strength of 486MPa with 2% elongation was recorded. This higher strength was caused by higher number density and finer precipitate size of η/ phase than other aging temperatures. The main hardening phase was identified to be the η/ phase while early nucleation of η phase in the higher aging temperature specimens resulted in lower strengths of the alloy. The activation energy for the precipitate hardening process of the alloy derived in this research was 95,827J/mol.
Article
Materials scientists and design engineers essentially have three choices when considering the method of manufacture for any metallic component: casting the liquid into a refractory mould or metal die; forging the solid in either the hot or cold condition, possibly between shaped dies; and machining, or a combination of these processes. Machining is wasteful of material, time consuming and generally involves expensive machinery, and many modern high performance materials are difficult or impossible to machine. Although forging has certain advantages over casting, the intricate shapes and good surface finish combined with dimensional accuracy and cheapness achievable in good die castings cannot be approached by forging. Semi-solid processing is potentially a technique in which components can be formed to near-net shape in a single operation. It promises to combine the ability to form complex shapes at the speed and cheapness of diecasting with the good mechanical properties and internal soundness possessed by forgings.
During dendritic solidification of castings and ingots, a number of processes take place simultaneously within the semisolid region. These include crystallization, solute redistribution, ripening, interdendritic fluid flow, and solid movement. The dendritic structure which forms is greatly affected by convection during the early stages of solidification. In the limit of vigorous convection and slow cooling, grains become spheroidal. Alloys with this microstructure possess rheological properties in the semisolid state which are quite different from those of dendritic alloys. They behave thixotropically, and viscosity can be varied over a wide range, depending on processing conditions. The metal structure and its rheological properties are retained after solidification and partial remelting. The semisolid alloys can be formed in new ways, broadly termed «semisolid metal (SSM) forming processes». Some of these are now employed commercially to produce metal components and are also used to produce metal-matrix composites
Article
The rheo-diecasting (RDC) process is an innovative one-step semisolid processing technique for manufacturing near-net shape components of high integrity directly from liquid Mg-alloys. The process innovatively adapts the well-established high shear dispersive mixing action of the twin-screw mechanism to the task of in situ creation of semisolid metal (SSM) slurry with fine and spheroidal solid particles followed by direct shaping of the SSM slurry into a near-net shape component using the existing cold chamber high pressure diecasting (HPDC) process. In this paper, we present the RDC process, and the resulting microstructures and mechanical properties of various Mg-alloys. The experimental results show that the RDC samples have extremely low porosity (typically 0.1–0.3%), fine and uniform microstructure throughout entire casting, and consequently much improved strength and ductility, compared with those produced by the HPDC process and other semisolid processes. In addition, the RDC process is more tolerant to alloy composition in terms of processability.
Article
The continuous rheoconversion process (CRP) is a novel slurry-on-demand process that was developed at MPI/WPI in 2002. The process is based on a passive liquid mixing technique in which the nucleation and growth of the primary phase are controlled using a specially designed "reactor". The reactor provides heat extraction, copious nucleation, and forced convection during the initial stage of solidification, thus leading to the formation of globular structures. This paper presents our recent work on the scale-up of the CRP for industrial applications. Specifically, we demonstrate an important application of the CRP to low temperature (low fraction solid) HPDC. In Part I of this paper, we present salient results on microstructural characterization of CRP processed castings vs. conventional die castings.
Article
Various processing methods exist for applying agitation to a molten metal during solidification to obtain metal slurries suitable for semi-solid metal processing. . In this paper, a new technique to achieve semi-solid metal structure using agitation during solidification is reported. The technique applies a new medium and means to efficiently create semi-solid metal structures. The results of a systematic study showing the feasibility and the necessary conditions to achieve the structure are discussed.
Article
A simple and efficient rheocasting process that has recently been invented is being developed for aluminum die casting applications. The process called Gas Induced Semi-Solid (GISS) utilizes the combination of local rapid heat extraction and agitation achieved by the injection of fine gas bubbles through a graphite diffuser to create semi-solid slurry. In the GISS process, the die casting machine and the process cycle remain little changed from those of conventional die casting. The GISS unit creates a low solid fraction of semi-solid slurry in the ladle during the ladle transfer to the shot sleeve. The semi-solid slurry is then poured directly into the shot sleeve. This paper presents the detailed description of the process. The results of the semi-solid die casting experiments with ADC10 alloy using the GISS process are also reported and discussed.
Article
Semisolid metal (SSM) processingis a relatively new technology for metal forming. Different from the conventional metal forming technologies which use either solid metals (solid state processing) or liquid metals (casting) as starting materials, SSM processing deals with semisolid slurries, in which non-dendritic solid particles are dispersed in a liquid matrix. Semisolid metal slurries exhibit distinctive rheological characteristics: the steady state behaviour is pseudoplastic (or shear thinning), while the transient state behaviour is thixotropic. All the currently available technologies for SSM processing have been developed based on those unique rheological properties, which in turn originate from their non-dendritic microstructures. Year 2001 marks the 30th anniversary of the concept of SSM processing. Today, SSM processing has established itself as a scientifically sound and commercially viable technology for production of metallic components with high integrity, improved mechanical properties, complex shape, and tight dimensional control. Perhaps more importantly, it has demonstrated its great potential for further technological development andcommercial exploitation. In this paper, progress made on the scientific understanding, technological development, and industrial applications of SSM processingare reviewed. The areas for further research and development are also discussed.
Article
Semisolid metal processing is a relatively new method for forming alloys in the semisolid condition to near net shaped products. It relies on the behaviour of semisolid slurries in which the solid exists in the form of spheroidal particles: if left undisturbed such slurries are stiff and may be handled, but flow like liquids on being sheared. Slugs of semisolid alloy may therefore be injected into a die (thixocasting) or shaped between closed dies (thixoforging) to produce components near-to-shape with good surface finish, free from porosity, and possessing fine uniform microstructures, which may be heat treated to give superior mechanical properties. The rheology of non-dendritic alloy slurries and the recent ideas which have been proposed to account for their pseudoplastic and thixotropic behaviour are considered. This is followed by a description of the technologies available for producing non-dendritic structures and the processes for subsequently shaping the semisolid alloy. Finally, some indication is given of the mechanical properties of components produced by the semisolid processing route.
Article
Experimental results are summarized of the formation of spheroidal grain structures in an Al-4.5 wt pct Cu alloy by (1) isothermally holding very fine equiaxed dendrites in the liquid-solid region and (2) direct spheroidal solidification from the melt. The fine-grained dendritic structure was obtained by very rapid solidification in a thin-section (0.8 mm) permanent-mold plate casting under conditions such that solidification took place during the filling process and, hence, during rapid fluid flow. Grains of approximately 30 µm in diameter (representing a grain density of about 3×104 mm−3) were obtained; these ripened to a spheroidal morphology in the liquid-solid region in less than 5 seconds. A similarly high grain count was then obtained in the bulk melt by vigorous agitation and rapid cooling near the liquidus temperature; the melt was thereafter cooled more slowly. Under these conditions, a spherical morphology formed early in solidification and grew in that form. The evolution of particle size with time in the liquid-solid region is shown to be essentially identical in the initially dendritic and spherical-growth experiments.
Article
A new approach to evaluate the solid fraction of semi-solid slurries is reported. The approach applies a thin-channel vacuum mold to rapidly quench semi-solid slurries at different rheocasting times. The slurry temperatures are analyzed from the cooling curves. The corresponding solid fraction data are obtained from standard quantitative metallography. A correction of the data is then conducted using the average growth layer of the solid particles. The analyzed solid fraction agrees well with the data from the Scheil model.
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