The object of this work is to investigate the influence of process parameters on drilling characteristics of an Al 1050 sheet with a thickness of 0.2 mm using a pulsed Nd:YAG laser through numerical analyses and experiments. By comparing the numerical analyses with the experiments, a proper numerical model was obtained. From the results of the numerical analyses and the experiments, the effects of process parameters on entrance diameters of drilled holes, shapes of the holes, taper angles of the holes and temperature distributions in the vicinity of the holes were examined quantitatively. In addition, the optimal drilling condition was estimated to improve the quality of the drilled holes.
Anodization of rare earth-containing Mg alloy of Mg-3Nd-0.2Zn-0.4Zr (mass fraction, %) (NZ30K) was performed in composite electrolyte containing NaOH, KOH, K2SiO3, Na2SiO3, NaF, KF etc. The anodic coating was characterized by using X-ray diffraction(XRD), field emission electron scanning microscope(FE-SEM) and electron probe microscopic analysis(EPMA). The corrosion resistance of the anodized alloy and the substrate was evaluated in 5% NaCl solution using electrochemical impedance spectroscopy(EIS). The results of XRD show that the anodic coating is mainly composed of MgO. EPMA indicates that magnesium and oxygen are almost uniformly distributed across the coating, and the fluorine content decreases gradually from the interface of coating-substrate to the surface, whereas the distribution of silicon is reverse to that of fluorine. The results of EIS analysis shows that the anodic coating exhibits the superior corrosion resistance for NZ30K alloy.
The La0.7Mg0.3Ni2.55-xCo0.45Cux (x=0, 0.1, 0.2, 0.3, 0.4) electrode alloys were prepared by casting and rapid quenching. Ni in the alloy was partially substituted by Cu in order to improve the cycle stability of La-Mg-Ni system (PuNi3-type) hydrogen storage alloy. The effects of substituting Ni with Cu on the microstructures and cycle stability of the alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the substitution of Cu for Ni is favourable for the formation of an amorphous in the as-quenched alloy, and this leads to an obvious refinement of the as-quenched alloy gains and a growth of the lattice constants and cell volumes of the as-cast and quenched alloys. The results obtained by the electrochemical measurement indicate that the cycle stability of the alloys significantly rises with the incremental variety of Cu content. When Cu content changes from 0 to 0.4, the cycle lives of the as-cast and quenched (30 m/s) alloys are enhanced from 72 to 88 cycles and from 100 to 121 cycles, respectively.
The purpose of this study is to predict the morphologies in the solidification process for Cu-0.6Cr (mass fraction, %) alloy by vacuum continuous casting (VCC) and verify its accuracy by the observed experimental results. In numerical simulation aspect, finite difference (FD) method and modified cellular automaton (MCA) model were used to simulate the macro-temperature field, micro-concentration field, nucleation and grain growth of Cu-0.6Cr alloy using real data from actual casting operations. From the observed casting experiment, the preliminary grain morphologies are the directional columnar grains by the VCC process. The solidification morphologies by MCAFD model are in agreement with the result of actual casting experiment well.
The influence of Ce implantation into preformed scales with a dose of 1×1017 ions/cm2 on the subsequent oxidation behavior of GH128 alloy at 1 000 °C in air was investigated. The pre-oxidation was carried out at 1 000 °C in air for 1 h and 5 h respectively. Cr2O3, NiO and NiCr2O4 formed on the surface of all specimens. Ce implantation decreased the subsequent oxidation rate of both the alloy and the 1 h pre-oxidized alloy, however, had no effect on that of the 5 h pre-oxidized alloy. The beneficial effect was most obvious in the directly implanted alloy. During the cyclic oxidation for 600 h, Ce implantation for all specimens with or without preferential oxidation played a similar beneficial effect on the oxide spallation resistance. The results indicate that Ce incorporated into the oxide scales affects the diffusion of the reaction species to some extent, the wavy interface and small grain structure make a significant contribution to improving the spallation resistance of the oxide scales.
The structural and electronic properties of bulk and (001) plane of TiC were investigated by the first-principles total-energy pseudopotential method based on density functional theory. The calculated bulk properties indicate that bonding nature in TiC is a combination of ionicity, covalency and metallicity, in which the Ti-C covalent bonding is the predominate one. The calculated results of structural relaxation and surface energy for TiC(001) slab indicate that slab with 7 layers shows bulk-like characteristic interiors, and the changes of slab occur on the outmost three layers, which shows that the relaxation only influences the top three layers. Meanwhile, the strong Ti-C covalent bonding can be found in the distribution of charge density on the (110) and (001) planes. Ti-C covalent bonding is enhanced by the charge depletion and accumulation in the vacuum and the interlayer region between top two atomic layers.
Effects of two typical surfactants, Tween-80 and sodium isobutyl-xanthate (NaIBX), with different concentrations on the growth and sulfur-oxidizing activities of a new strain Acidithiobacillus albertensis BY-05, an acidophilic sulfur-oxidizing bacterium, were investigated. The results indicate that both surfactants can enhance the growth and sulfur-oxidizing activities of A. albertensis BY-05 only at some special concentrations, e.g., 10−4–10−8 g/L for NaIBX and lower than 10−8 g/L for Tween-80, but were inhibited and even harmful at higher concentrations. Both surfactants can not be metabolized by A. albertensis BY-05. The contact between the bacteria and the sulfur particles may be dependent upon both the extracellular substance and the surfactants, both of which provide the amphiphilic environment improving the attachment for bacteria to the sulfur particles surface. These data could be significant for enlarging the applications of both A. albertensis BY-05 and some typical surfactants for industrial bioleaching of sulfides minerals.
An acidophilic, rod-shaped Gram-negative sulfur oxidizing strain BY-05 was isolated from an acid mine drainage of copper ore in Baiyin area, Gansu Province, China. Ultrastructural studies show that the isolate has a tuft of polar flagella and possesses sulfur granules with clear membrane adhering to the cell innermembrane. Physiological study shows that this isolate grows autotrophically and aerobically by oxidizing S0 and reduced inorganic sulfur compounds (S2O2-3, S2O2-4, S2- and ZnS) with the optimum growth at pH 3.5–4.0 and at the temperature range of 25–30 °C. The 16S rRNA gene sequence (DQ 423683) of strain BY-05 has 100% sequence similarity to that of Acidithiobacillus albertensis (DSM 14366). So it is identified and named as A. albertensis BY-05. Bioleaching experiments with this new strain show that it can play an important role in recovery of metals from chalcopyrite and sphalerite.
A series of experiments were conducted for AI-1.65%Si (mass fraction) alloy melt to study the formation of grain refining structure with ultrasonic stirring. The cooling curves of ingots with ultrasonic were measured and compared with those without ultrasonic. At the same time, the effect of the time of ultrasonic stirring on solidification structure of ingots was investigated. The influence of ultrasonic on the grain-refining efficiency of ingots was analyzed. In order to well understand the melts behavior under ultrasonic, by using ammonium chloride solution, the simulation experiment was carried out and the temperature distribution in ingot with or without ultrasonic was compared. The results indicate that the ultrasonic reduces the temperature inhomogeneity of melt, i.e the ultrasonic helps to homogenize the melt temperature. The effect of stirring and heat generation in ingot start to occur with increasing the time of ultrasonic stirring.
The isothermal oxidation behavior of a Ti3Al-based alloy (Ti-24Al-14Nb-3V-0.5Mo-0.3Si, molar fraction, %) at 700– 1 000 °C in air was investigated. The oxidation kinetics of tested alloy approximately obeys the parabolic law, which shows that the oxidation process is dominated by the diffusion of ions. The oxidation diffusion activity energy is 241.32 kJ/mol. The tested alloy exhibits good oxidation resistance at 700 °C. However, when the temperature is higher than 900 °C, the oxidation resistance becomes poor. The XRD results reveal that the oxide product consists of a mixture of TiO2 and Al2O3. Serious crack and spallation of oxide scale occur during cooling procedure after being exposed at 1 000 °C in air for 16 h. According to the analysis of SEM/EDS and XRD, it is concluded that the Al2O3 oxide forms at the initially transient oxidation stage and most of it keeps in the outer oxide layer during the subsequent oxidation procedure.
A modified analytic embedded-atom model(MAEAM) was applied to investigate surface premelting and melting behaviors of Nb(111) plane by molecular dynamics(MD) simulations. First the relaxation of surface interface space at 300 K was studied. Then a number N of the disordered atoms per unit area was determined at the given temperatures to investigate the surface premelting and melting evolution. The obtained results indicated that the premelting phenomena occurred at about 1 100 K and a liquid-like layer emerged on (111) plane simultaneously. As temperature increased up to 2 200 K, the number N grew logarithmically for short-range metallic interactions. Upon 2 350 K surface melting generated originally and the number N increased exponentially with the incremental temperature.
In laser welding-brazing of Al alloy (5A06) and Ti alloy (Ti-6Al-4V) with rectangular CO2 laser spot and with Al-12Si filler wire, element Si enriches at the interface between Ti substrate and the filler metal. It is found that the Si diffusion behavior has a significant effect on the formation of interfacial intermetallic compounds. To analyze the Si diffusion behavior, a model for the prediction of the chemical potential for ternary alloy was established. According to the calculated results of the influence of the element content and temperature in Ti-Al-Si system on Si chemical potential, the diffusion behavior of Si element was analyzed for Ti dissolution and melting mode, which presents a good agreement with the experimental data. Further, formation mechanism of the interfacial intermetllic compound was clarified.
Carcinogenesis of lung squamous carcinoma is a complex process involving multiple events and steps. At present, there are very few special lung cancer molecular markers for an “early-stage” diagnosis and prognosis evaluation. To identify tumor-associated antigens, serological proteome analysis (SERPA) of human lung squamous carcinoma cell line HTB-182 are performed. We characterized sixteen differentially expressed proteins which react with lung squamous carcinoma patient sera while not react with control sera. Some of these candidate lung squamous carcinoma-associated antigens were metabolic enzymes, such as triosephosphatase isomerase (TPIS). Some proteins were involved in the regulation of cell cycle and signal transduction. The results will provide scientific foundation for screening the molecular biomarkers used to diagnose and treat lung squamous carcinoma, as well as to elevate the patient's prognosis and provide new clue for the research of lung squamous carcinogenic mechanism. Thus, SERPA represents a valuable approach for the identification of differentially expressed proteins, which might be used as markers for the diagnosis and prognosis of lung squamous carcinoma.
Both Mg-1Mn-3.5Y and Mg-1Mn-1Y-2.5Nd alloys (mass fraction, %) were extruded at 380 °C. Most of the (100) crystal planes in the Mg-1Mn-3.5Y alloy are parallel to the normal direction, while most of the (101) crystal planes in the Mg-1Mn-1Y-2.5Nd alloy are parallel to the normal direction. The tensile tests at room temperature, 100 °C and 200 °C show that the Mg-1Mn-3.5Y alloy exhibits higher yield strength, but lower elongation to failure as compared with the Mg-1Mn-1Y-2.5Nd alloy. These differences in the tensile mechanical properties between the two alloys are mainly attributed to their different texture types and amount and distribution of the Mg24Y5 precipitates. The serration flow behavior is observed in the Mg-1Mn-1Y-2.5Nd alloy at 200 °C, but does not occur in the Mg-1Mn-3.5Y alloy. The Mg-1Mn-3.5Y alloy shows the cleavage fracture mode, while the Mg-1Mn-1Y-2.5Nd alloy exhibits the dimple fracture mode.
The surface liquid segregation (SLS) phenomenon in semi-solid metal-high pressure die casting (SSM-HPDC) plates of 7075, 2024, 6082 and A201 was investigated by different techniques. Depth profiles were determined by firstly measuring the chemical composition of the surface of the plates using a Thermo Quantris optical emission spectrometer (OES). Material was then removed by a grinding process followed by measurement of the amount of material removed and chemical analysis. Chemical profiles of the main alloying elements were plotted for the cross-section of the plates in the as-cast and T6 (after solution treatment) temper conditions. Vickers hardness profiles from the surface to the centre of the plates were determined. Metallographic samples of cross-sections of the castings were prepared and evaluated using a scanning electron microscope. The results show that surface liquid segregation in SSM-HPDC alloys causes significant differences in properties between the surface and the bulk of these castings in both the F and T6 temper conditions.
A two-step reheating process was proposed and applied to perform reheating experiments on the semi-solid 2024 alloy billet. In this process, the semi-solid billet was firstly heated over liquidus temperature and then isothermally held at solid-liquid zone temperature. Microstructure evolution of the semi-solid billet during two-step reheating was studied by optical microscope and compared with that during isothermal reheating. The results show that the remelting rate of the semi-solid billet during two-step reheating is faster than that during isothermal reheating. Under the same reheating time, the grains of the semi-solid billet reheated by two-step reheating process are finer and rounder than those by isothermal reheating process. The present experimental results indicate that accelerating the formation of liquid phase during the two-step reheating process can restrain the coalescence of grains to a certain extent, and thus refine the grain size and promote the grain spheroidization.
The semi-solid slurry of wrought aluminum alloy 2024 was prepared by a well developed rheocasting process, low superheat pouring with shearing field(LSPSF). The appreciate combination of pouring temperature and rotation speed of barrel, can give rise to a transition of the growth morphology of primary α(Al) from coarse-dendritic to coarse-particle-like and further to fine-globular. The combined effects of both localized rapid cooling and vigorous mixing during the initial stage of solidification can enhance wall nucleation and nuclei survival, which leads to the formation of fine-globular primary α(Al). By using semi-solid slurry prepared by LSPSF, direct squeeze cast cup-shaped component with improved mechanical properties such as yield strength of 198 MPa, ultimate tensile strength of 306 MPa and elongation of 10.4%, can be obtained.
P and RE complex modification of hypereutectic Al-Si alloys was conducted. The influences of P, RE content on the microstructure and mechanical properties of alloys were investigated. The complex modifications of P and RE make the coarse block primary silicon obviously refined and the large needle eutectic silicon modified to the fine fibrous or lamella ones. P mainly refines the primary silicon, but excess P is unfavorable to the refinement of primary silicon. RE can well refine the primary and eutectic silicon, but its modification effect on the eutectic silicon is more obvious. P can repress the modification of RE on the eutectic silicon. The alloys with the additions of 0.08% P and 0.60% RE have the optimal microstructure and the highest mechanical properties. Compared with the unmodified alloy, the primary silicon of alloys can be refined from 66.4 μm to 23.3 μm and the eutectic silicon can be refined from 8.3 μm to 5.2 μm. The tensile strength is improved from 256 MPa to 306 MPa and the elongation is improved from 0.35% to 0.48%.
Microstructures of three kinds of typical product states for commercially fabricated alloy 2195 were observed. It is found that the hot-rolled plate is characterized by a fibrous structure containing fine, polygonized substructures; and the cold-rolled sheet was characterized by a “pan-caked” grain structure containing high density dislocation cells. The product under near peak-aging temper is proved to contain a large amount of dispersive, plate-shaped T1(Al2CuLi) precipitates, together with a small fraction of theta;'(Al2Cu) plates, exhibiting a desirable combination of mechanical properties. Analyses using scanning electron microscopy reveal that many coarse, irregular-shaped Al7Cu2Fe constituent particles exist in all product states, which indicates that intermediate heat treatments have little influence on this iron-caused, detrimental phase. The formation and evolution of microstructures for different product states of alloy 2195 were discussed in view point of the commercial production condition.
To effectively monitor the characteristic of Acidithiobacillus ferrooxidans ATCC 23270 at the whole-genomic level, a whole-genome 50-mer-based oligonucleotide microarray was developed based on the 3 217 ORFs of A. ferrooxidans ATCC 23270 genome. Based on artificial oligonucleotide probes, the results showed that the optimal hybridization temperature was 45°C. Specificity tests with the purified PCR amplifications of 5 genes (Sulfide-quinone reductase, Cytochrome C, Iron oxidase, Mercuric resistance protein, Nitrogenase iron protein) of A. ferrooxidans ATCC 23270 indicated that the probes on the arrays appeared to be specific to their corresponding target genes. Based on the WGA hybridization to global transcriptional difference of A. ferrooxidans ATCC 23270 strains cultured with Fe(II) and S(0), the developed 50-mer WGA could be used for global transcriptome analysis of A. ferrooxidans ATCC 23270. The detection limit was estimated to be approximately 5 ng with the genomic DNA, and at 100 ng of the DNA concentration, all of the signals reached the saturation. In addition, strong linear relationships were observed between hybridization signal intensity and the target DNA concentrations (r2=0.977 and 0.992). The results indicated that this technology had potential as a specific, sensitive and quantitative tool for detection and identification of the strain A. ferrooxidans ATCC 23270 at the whole-genome level.
The effect of vacuum heat treatment on the microstructure and microhardness of cold-sprayed Cu-4%Cr-2%Nb alloy coating was investigated. The heat treatment was conducted under the temperatures from 250 °C to 950 °C with a step of 100 °C for 2 h. It was found that a dense thick Cu-4Cr-2Nb coating could be formed by cold spraying. After heat treatment, a Cr2Nb phase was uniformly distributed in the matrix, which was transferred from the gas-atomized feedstock. A little grain growth of Cr2Nb phase was observed accompanying with the healing-up of the incomplete interfaces between the deposited particles at the elevated temperatures. The coating microhardness increases a little with increasing the temperature to 350 °C, and then decreases with further increasing temperature up to 950 °C. This fact can be attributed to the microstructure evolution during the heat treatment.
In order to study the effect of the stirring flow on the grain diameter and solute concentration of hollow billet, the couple model of the two-phase solidification and electromagnetic field was built to simulate the solidification process of Sn-3.5%Pb hollow billet with the traveling magnetic field and rotating magnetic field. The effects of different kinds of flows on the temperature field, concentration field and grain diameter of molten metal during solidification were analysed. The results show that, there are different flow patterns in the molten metal induced by the traveling magnetic field and rotating magnetic field. Both flows can refine the grains in the hollow billet because of change of the temperature gradient and cooling rate of molten metal. The bigger the stirring velocity is, the smaller the grain diameter. Both flows can result in the macro-segregation in the hollow billet because of the non-homogeneous flows. The bigger the stirring velocity, the more serious the macro-segregation of the hollow billet. So, the stirring intensity should be controlled to acquire the high quality hollow billet.
Highly porous 316L stainless steel parts were produced by using a powder metallurgy process, which includes the selective laser sintering(SLS) and traditional sintering. Porous 316L stainless steel suitable for medical applications was successfully fabricated in the porosity range of 40%-50% (volume fraction) by controlling the SLS parameters and sintering behaviour. The porosity of the sintered compacts was investigated as a function of the SLS parameters and the furnace cycle. Compressive stress and elastic modulus of the 316L stainless steel material were determined. The compressive strength was found to be ranging from 21 to 32 MPa and corresponding elastic modulus ranging from 26 to 43 GPa. The present parts are promising for biomedical applications since the optimal porosity of implant materials for ingrowths of new-bone tissues is in the range of 20%-59% (volume fraction) and mechanical properties are matching with human bone.
Stir casting is one of the simplest ways of producing aluminum matrix composites. However, it suffers from poor incorporation and distribution of the reinforcement particles in the matrix. These problems become especially significant as the reinforcement size decreases due to greater agglomeration tendency and reduced wettability of the particles with the melt. Development of new methods for addition of very fine particles to metallic melts which would result in more uniform distribution and effective incorporation of the reinforcement particles into the matrix alloy is therefore valuable. In this work, 356-5%SiCp (volume fraction) composites, with average SiCp sizes of about 8 and 3 μm, were produced by injection of different forms of the reinforcement particles into fully liquid as well as semisolid slurries of 356 aluminum alloy and the effects of the injected reinforcement form and the casting method on distribution of the reinforcement particles as well as their porosity, hardness and impact strength were investigated. The results reveal that addition of SiC particles in the form of (Al-SiCp)cp composite powder and casting in semisolid state decreases the SiCp particle size, enhances the wettability between the molten matrix alloy and the reinforcements and improves the distribution of the reinforcement particles in the solidified matrix. It also increases the hardness and the impact energy of the composites and decreases their porosity.
AbstractA first-principles plane-wave pseudopotential method based on the density functional theory was used to investigate the energy and electronic structure of magnesium hydride (MgH2A) alloyed by 3d transition metal elements. Through calculations of the negative heat formation of magnesium hydride alloyed by X (X denotes 3d transition metal) element, it is found that when a little X (not including Sc) dissolves into magnesium hydride, the structural stability of alloying systems decreases, which indicates that the dehydrogenation properties of MgH2 can be improved. After comparing the densities of states(DOS) and the charge distribution of MgH2 with or without X alloying, it is found that the improvement for the dehydrogenation properties of MgH2 alloyed by X attributes to the fact that the weakened bonding between magnesium and hydrogen is caused by the stronger interactions between X (not including Cu) and hydrogen. The calculation results of the improvement for the dehydrogenation properties of MgH2-X (X=Ti, V, Mn, Fe, Co, Ni, Cu) systems are in agreement with the experimental results. Hence, the dehydrogenation properties of MgH2 are expected to be improved by addition of Cr, Zn alloying elements.
The dry friction and wear behavior of 7075 Al alloy reinforced with SiC 3D continuous ceramic network against Cr12 steel was studied with oscillating dry friction and wear tester under the testing conditions of 70 °C, 30 min, and the load range of 40–100 N. The experimental result shows that the characteristic of abrasive wear and oxidation wear mechanisms are present for 3D continuous SiC/7075 Al composite. 3D continuous network ceramic as the reinforcement can avoid composite from the third body wear that usually occurs in traditional particle reinforced composite. Under low load, the composite with low volume fraction of ceramic reinforcement exhibits better wear resistance due to the homogeneous reinforcement distribution with small pore size; on the contrary, under high load, the composite with high reinforcement volume fraction exhibits better wear resistance because of the coarse frame size. Hard SiC frame leads to the wear of Cr12 steel mainly. The frame with high volume fraction corresponds to the high Fe content.
The outside serrated integral-fin tubes fabricated by rolling-plowing-extrusion processing were surface-treated through different processes of annealing in hydrogen atmosphere, electrochemical corrosion or sandblasting. The purpose was to eliminate residual stress, clear secondary micro-fins and enhance heat transfer performance. By comparing the surface characteristics, it is found that the finned tubes treated by electrochemical corrosion have the most glabrous surfaces where the fins are almost perfectly reserved. Clear layer cracks can be observed on the top of the fins. These structures are effective in enhancing heat transfer performance when being applied to flow heat exchange. Therefore, the finned tubes treated by electrochemical corrosion are proper for the tubular exchanger with water coolant. The finned tubes treated by sandblasting have rougher surfaces with layer cracks and micro gaps removed. As these structures are useful to clearing adhesive feculence, the tubes are more suitable for the tubular heat exchanger with oil coolant.
The deflection of rolls of Sendzimir mill with double AS-U-Roll was simulated by finite element method(FEM). The influences of rolling pressure, strip width and rolls-assignment on rolls deflection were analyzed. The results show that the work roll deflection increases with the increase of rolling pressure and the reduction of work roll radius, but the rigid displacement of work roll slightly changes; the work roll end might appear negative displacement for the narrow strip width and high rolling pressure that might cause the contact of work rolls. The research results are significant for guiding production and theoretical analysis of the rolls system of Sendzimir mill.
AbstractSolvothermal technique, an one-step soft solution-processing route was successfully employed to synthesize single crystalline CdS nanowires in ethylenediamine medium at lower temperature (170 □) for 1–8 d. In this route, polyethylene glycol 400 (PEG400) was used as surfactant, which played a crucial role in preferentially oriented growth of semiconductor nanowires. Characterizations of as-prepared CdS nanowires by X-ray powder diffraction(XRD), transmission electron microscopy(TEM) indicate that the naonowires, with typical diameters of 20nm and lengths up to several micrometers, have preferential  orientation. Also, investigations into the physical properties of the CdS nanowires were conducted with UV-Vis absorption spectroscopy and photoluminescence emission spectroscopy. The excitonic photo-optical phenomena of the nanowires shows the potential in the practical applications.
The microstructure and mechanical properties of rheocasted 5052 aluminum alloy were investigated. The semi-solid slurry of this alloy was prepared by ultrasonic vibration (USV) process and then shaped by gravity casting (GC) and high press diecasting (HPDC). The experimental results indicate that fine and globular primary a(Al) particles are distributed uniformly in the rheocasting samples. The tensile strength and elongation of the rheo-GC sample are 191 MPa and 7.5%, respectively. Compared with the conventional GC samples, they increase by 22.4% and 82.9% respectively. The tensile strength and elongation of the rheo-HPDC samples reach 225 MPa and 8.6%, respectively, and they are 14.8% and 75.5% higher than those of the conventional HPDC samples, respectively. It is also found that the ductile fracture mode prevails in the rheocasting samples.
AA 6061-T6 aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high specific strength and good corrosion resistance. Compared with the fusion welding processes that are routinely used for joining structural aluminium alloys, friction stir welding (FSW) process is an emerging solid state joining process in which the material welded does not melt and recast. Joint strength is influenced by the grain size and tensile strength of the weld nugget region. Hence, an attempt was made to develop empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints. The empirical relationships are developed by response surface methodology (RSM) incorporating FSW tool and process parameters. A linear regression relationship was also established between grain size and tensile strength of the weld nugget of FSW joints.
Based on rolling tests and simulation, the bond behavior and its mechanism of 6111-aluminum alloy commonly used in auto industry were studied. As main factors, the effects of different heating stratagem, rolling speed and reduction on bond were tested. The effect of rolling speed on bond was produced by the synthetical result of contact time and temperature of rolling zone. Higher speed creates higher temperature of rolling zone but decreases contact time of interfaces, and bond strength decreases accordingly. The bond strength increases along with the increase of entry temperature before a turning point, after the turning point bond strength changes gently. Cold rolling is hard to get a satisfying bond result although the rolling parameters are adjusted, while warm bond reaches a higher strength that is comparable to the parent material. The analysis of surfaces separated by shear test shows that for warm bonding the rolling texture disappears on the bond area but the scratch track remain on the bond area for cold bond. There is no gap at the position of interface for well-bond sample. The results of this study are helpful to create well-bond materials for auto industry.
It is economically advantageous to cast wrought aluminum alloys directly into near-net-shape components. The objective of the present work is to take advantage of the rheoforming with 7075 alloy to improve the competitiveness of this emerging technology in the manufacture of wrought aluminum alloy. High quality semi-solid slurry was produced, in which primary a (Al) presents in diameter of 62 μm and shape factor of 0.78 and features no eutectics entrapped. Higher forming pressure results in small grain size, improved shape factor and higher density. Especially, rheoforming can effectively reduce the occurrence of hot tearing. The average yield strength and elongation of the rheoformed samples in the T6 condition are 483 MPa and 8%, respectively.
The influence of two novel aging treatments, T6I6 (130 °C, 80 min + 65 °C, 240 h+130 °C, 18 h) and high-temperature pre-precipitation(HTPP) aging (445 °C, 30 min+120 °C, 24 h) on the tensile properties, intergranular corrosion, exfoliation corrosion behaviors and microstructures of 7075 Al alloy was studied, which were compared with the T6, T73 and RRA treatments. Fine η′ precipitate with high density was obtained in the alloy with the T6 and RRA treatments. The η′ precipitate density in the HTPP aged alloy is decreased due to the formation of coarse particles during the pre-precipitation process at high temperature of 445 °C. The 7075-T6I6 alloy possesses higher precipitate density and whole precipitate volume fraction within the grain than the 7075-T73 alloy, and its whole precipitate volume fraction is even greater than that of the 7075-T6 alloy. Compared with T6 treatment, the RRA, T73, T6I6 and HTPP aging treatments cause the discontinuous distribution of the η precipitates at the grain boundary, which decreases the intergranular corrosion and exfoliation corrosion susceptibility of the alloy. Meanwhile, the T6I6 and RRA treatments can keep the high strength of the 7075 Al alloy, but the studied HTPP aging and T73 treatments lower its strength.
The adsorption properties of the four precious metal ions (Ag(I), Au(II), Pd(III) and Pt(IV)) on the commercial Cl−-form 717 strongly basic anion-exchange resin were studied in detail. The effects of the contact time, solution acidity, and concentrations of Cl− and Pb2+ ions on the adsorption properties were studied by the batch method. Then, the column method was conducted under the optimized adsorption conditions (pH=3.0). The effects of the sample loading flow rate and the length-to-diameter ratios of the columns were investigated. The precious metal ions adsorbed could not be eluted completely after the saturated adsorption because the precious metal ions were found to be reduced to their metallic states during the adsorption process. So, it is recommended that the commercial Cl−-form 717 strongly basic anion-exchange resin should be decomposed directly to recovery the precious metals after the saturated adsorption.
Recently, laser cutting technologies begin to use for manufacturing mechanical parts of Inconel super-alloy sheet due to difficulties of machining of the Inconel material as a results of its extremely tough nature. The objective of this work is to investigate the influence of cutting parameters on surface characteristics of the cut section in the cutting of Inconel 718 super-alloy sheet using CW Nd:YAG laser through laser cutting experiments. Normal cutting experiments were performed using a laser cutting system with six-axis controlled automatic robot and auto-tracking system of the focal distance. From the results of the experiments, the effects of the cutting parameters on the surface roughness, the striation formation and the microstructure of the cut section were examined. In addition, an optimal cutting condition, at which the surface roughness is minimized and both the delayed cutting phenomenon and the micro-cracking are not initiated, is estimated to improve both the part quality and the cutting efficiency.
A new method was exploited using solution treatment and aging process as a pretreatment in preparing semi-solid slurry with fine microstructure before isothermal treatment of wrought aluminum alloy 7A09. Parameters of pretreatment were optimized by orthogonal experiment design and proper precursor was prepared. The evolution of microstructure of semi-solid slurry during isothermal treatment was analyzed and the mechanism of microstructure refining was discussed. The result of orthogonal experiment design shows that the optimum parameters are 462 °C for solution temperature, 40 min for solution time, 132 °C for aging temperature and 14 h for aging time. Microstructure of isothermal treatment is fine, homogenous, with globular solid grains and a solid fraction between 50% and 70%, which is qualified for later semi-solid forming process. Mechanism of microstructure evolution includes the agglomeration of α-phase and Ostwald ripening. Precipitations prepared by solution and aging treatment prevent the grains from coarsening and promote the grain ripening to globular shape.
By using transmission electron microscopy, the microstructures of drawn industrial single crystal copper wires produced by Ohno Continuous Casting(OCC) process were analyzed. The results show that the typical microstructures in the wires mainly include extended planar dislocation boundaries, a small fraction of twins and some dislocation cells sharing boundaries parallel to drawn direction. Besides the typical microstructures, 9R structure configurations were observed in the wires. The formation of 9R polytypes may be caused by the coupled emission of Shockley dislocations from a boundary.
Pitting behavior of thixoformed A356 alloy, with different reheating temperatures, was evaluated. Linear sweep voltammetric tests were used to study the pitting behavior of thixoformed, rheocast and gravity-cast A356 alloy in a 3.5% NaCl solution. A simulation method was also used in order to identify local galvanic corrosion current density between local galvanic couples. The results obtained show that the resistance to pitting corrosion of the thixoformed samples formed at 600 °C is higher than that of the samples formed at 610 °C as well as rheocast and gravity-cast samples. These results could be explained by morphological aspects of silicon phase as well as the area effect as related to galvanic corrosion between silicon particles and eutectic aluminum phase.
The semi-solid slurry of A356 alloy was prepared by low superheat pouring and slightly electromagnetic stirring, in which a pure copper rod was used to produce local chilling. The effect of chilling by the rod on morphology and size of primary α(Al) in A356 was researched. The results indicate that the chilling by the rod remarkably affects the morphology and the size of primary α(Al). Primary α(Al) with particle-like shape is distributed uniformly in A356, and there is no transient area in structure morphology. Compared with the samples prepared without the local chilling, the nucleation rate, morphology and grain size of primary α(Al) in A356 prepared by low superheat pouring and slightly electromagnetic stirring with the rod are markedly improved. Under the condition of chilling, the pouring temperature can be suitably raised to obtain primary α(Al) with particle-like shape.
A356 aluminum alloys reinforced with carbon nano-tubes (CNTs) were produced by stir casting and compocasting routes and their microstructural characteristics and hardness were examined. In order to alleviate the problems associated with poor wettability, agglomeration and gravity segregation of CNTs in the melt, CNTs were introduced into the melts by injection of CNT deposited aluminum particles instead of raw CNTs. Aluminum particles with mean diameters of less than 100 μm were first deposited by CNTs using Ni-P electroless plating technique and then injected into the melt agitated by a mechanical stirrer. The slurry was subsequently cast at temperatures corresponding to full liquid as well as 0.15 and 0.30 solid fractions. The results show that addition of CNTs to A356 matrix can significantly refine both full liquid and semi-solid cast microstructures. Hardness of the samples is also significantly increased by addition of CNTs and A356-CNT composite cast at 0.3 solid fraction produces the highest hardness.
The effects of slight electromagnetic stirring on morphology of primary phase in semisolid A356 prepared by low superheat pouring and slight electromagnetic stirring were researched, and some characteristic parameters characterized the morphology and grain size of the primary phase were calculated. The results indicate that the stirring power has an important effect on the morphology and the grain size. The characteristics of the morphology could be characterized by the fractal dimensions and the shape factors. The fractal dimension and the shape factor change when the morphology changes with processing conditions. Both increase with the increase of the stirring power, but the fractal dimension is still affected by the grain size. The increase of stirring power could obviously improve the grain size, fractal dimension and shape factor of the primary phase.
The fractal dimensions of primary phase morphology in semi-solid A356 alloy prepared by low superheat pouring and slightly electromagnetic stirring were calculated, and the effect of pouring temperature on fractal dimension of primary phase morphology in semi-solid A356 alloy was researched. The results indicate that it is feasible to prepare semisolid A356 alloy slurry by low superheat pouring and slightly electromagnetic stirring, and there is an important effect of pouring temperature on the morphology and the grain size of the primary phase in semi-solid A356 alloy, in which the reduction of pouring temperature can obviously improve grain size and shape factor of primary phase in semi-solid A356 alloy under the condition of a certain stirring power. The primary phase morphology of semi-solid A356 alloy prepared by low superheat pouring and slightly electromagnetic stirring can be characterized by fractal dimension, and the primary phase morphology obtained by the different processing parameters has the different fractal dimensions. Solidification of semi-solid alloy is a course of change in fractal dimension.
The effect of pouring temperature, electromagnetic stirring power and holding process on semi-solid A356 aluminum alloy slurry was investigated, then the slurry was squeeze-cast. The results show that when the pouring temperatures are properly above the liquidus line, for example 630-650 °C, the slurry with spherical primary α(Al) grains can be prepared under the stirring power of 1.27 kW. The slurry is then homogeneously held for a short time, and the primary α(Al) grains are further ripened and distributed evenly in the slurry. The results of the rheo-squeezed casting experiments show that the injection specific pressure has a great effect on the filling ability of the semi-solid A356 aluminum alloy slurry, and the higher the injection specific pressure is, the better the ability for the slurry to fill the mould cavity is. When the injection specific pressure is equal to or above 34 MPa, the whole and compact rheo-squeezed castings can be obtained. The microstructure of the castings indicates that the shape, size and numbers of the primary α(Al) grains in different parts of the castings are highly consistent. After being held at 535 °C for 5 h and then aged at 155 °C for 12 h, the ultimate strength of the rheo-squeezed castings can reach 300-320 MPa, the yield strength 230-255 MPa, and the elongation 11%-15%.
Since the automotive industry has many possible applications for semi-solid metal (SSM)-high-pressure die casting (HPDC) parts, the newly developed heat treatment cycles, as well as the traditional heat treatment cycles, were applied to A356 brake calipers cast using a LK DCC630 HPDC machine. Vickers hardness measurements at a cross section of the brake calipers were performed, indicating that similar values can be obtained when using the significantly shorter heat treatment cycles. Finally, the typical tensile properties that can be obtained for SSM-HPDC A356 brake calipers are compared with those manufactured by gravity die casting. Results indicate that the differences in microstructures (globular or dendritic) do not have a noteworthy effect on the heat treatment response. This implies that the short heat treatment cycles originally developed for globular SSM-HPDC A356 castings can be successfully applied to dendritic liquid A356 castings too.
The evolution of the grain structures in AA2195 Al-Li alloy plate warm-rolled by 80% reduction during recrystallization annealing at 500 °C was investigated by electron backscatter diffraction, scanning electron microscopy and transmission electron microscopy. It is found that the elongated grain structures are caused by the lamellar distribution of recrystallization nucleation sites, being lack of large second phase particles (> 1 μm), and dispersive coherent particles (such as δ′ and β′) concentrated in planar bands. The recrystallization process may be separated into three stages: firstly, recrystallization nucleation occurs heterogeneously, and the nuclei are concentrated in some planar zones parallel to rolling plane. Secondly, the grain boundaries interacted with small particles concentrate in planar bands, which is able to result in the elongated grain structures. The rate of the grain growth is controlled by the dissolution of these small particles. Thirdly, after most of small particles are dissolved, their hindrance to migration of the grain boundaries fades away, and the unrecrystallized zones are consumed by adjacent recrystallized grains. The migration of high angle grain boundaries along normal direction leads a gradual transformation from the elongated grains to the nearly equiaxed, which is driven by the tension of the grain boundaries.
Friction stir welding(FSW) is an innovative solid state joining technique and has been employed in aerospace, rail, automotive and marine industries for joining aluminium, magnesium, zinc and copper alloys. The FSW process parameters such as tool rotational speed, welding speed, axial force, play a major role in deciding the weld quality. Two methods, response surface methodology and artificial neural network were used to predict the tensile strength of friction stir welded AA7039 aluminium alloy. The experiments were conducted based on three factors, three-level, and central composite face centered design with full replications technique, and mathematical model was developed. Sensitivity analysis was carried out to identify critical parameters. The results obtained through response surface methodology were compared with those through artificial neural networks.
The simultaneous removal of Cr(VI) and phenol in a consortium culture containing Cr(VI) reducer, Bacillus sp. and phenol degrader, Pseudomonas putida Migula (CCTCC AB92019) was studied. Phenol was used as the sole carbon source. Bacillus sp. utilized metabolites formed from phenol degradation as electron donors and energy source for Cr(VI) reduction. Optimum Cr(VI) reduction was observed at a phenol concentration of 150 mg/L and an initial Cr(VI) concentration of 15 mg/L. Both the Cr(VI) reduction and phenol degradation were influenced by the cell composition of the culture, but the phenol degradation was not significantly affected by the content of Bacillus sp. The experiments also showed that the amount of phenol degraded was more than that stoichiometrically required for Cr(VI) reduction.
The laser ablation technique was employed to prepare TiO2 nanoparticles by pulsed laser ablation of a titanium target immersed in the poly-(vinylpyrrolidone) solution using wavelength of 1 064 nm. The as-prepared products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results indicate that the rutile TiO2 nanoparticles are synthesized at room temperature and the average size is about 35 nm with narrow size distribution. A possible formation mechanism was discussed and the UV-vis absorption and photoluminescence were measured. The optical study shows that rutile nanoparticle possesses direct optical transition with band gap of 3.15 eV.
Nanometer oxides La1−xSrxMnO3 were synthesized by absolute alcohol as solvent. The desired metal cations were chelated in a solution using citric acid as the chelating agents. In order to get the optimum preparation condition for La1−xSrxMnO3, the pH of primal commix solution, the molar fraction of citric acid and baking temperature of predecessor block were researched by orthogonal test design method with different x. The thermal decomposition of the metal carboxylate precursor gels was studied by TG/DTA and the products derived from calcinations of the gels were characterized by XRD and TEM. The polarization curves were acquired on an electrochemical work station (LK98) and the discharge curves were acquired on a testing instrument of batteries (DC-5) with a constant current discharge under 120 mA/cm2. The results reveal that the nanometer oxides can be achieved by absolute alcohol as solvent and it has better catalytic activity.