Wetting of molten Sn-3.5Ag-0.5Cu on Ni-P(-SiC) coatings deposited on high volume faction SiC/Al composite

The wetting of molten Sn-3.5Ag-0.5Cu alloy on the Ni-P(-SiC) coated SiC_p/Al substrates was investigated by electroless Ni plating process, and the microstructures of the coating and the interfacial behavior of wetting systems were analyzed. The SiC particles are evenly distributed in the coating and enveloped with Ni. No reaction layer is observed at the coating/SiC_p/Al composite interfaces. The contact angle increases from ～19° with the Ni-P coating to 29°, 43° and 113° with the corresponding Ni-P-3SiC, Ni-P-6SiC and Ni-P-9SiC coatings, respectively. An interaction layer containing Cu, Ni, Sn and P forms at the Sn-Ag-Cu/Ni-P-(0,3,6)SiC coated SiC_p/Al interfaces, and the Cu-Ni-Sn and Ni-Sn-P phases are detected in the interaction layer. Moreover, the molten Sn-Ag-Cu can penetrate into the Ni-P(-SiC) coatings through the Ni-P/SiC interface and dissolve them to contact the SiC_p/Al substrate.     

Influence of powder particle injection velocity on the microstructure of Al-12Si/SiCp coatings produced by laser cladding

The influence of powder particle injection velocity on the microstructure of coatings consisting of an Al-Si matrix reinforced with SiC particles prepared by laser cladding from mixtures of powders of Al-12 wt.% Si alloy and SiC was investigated both experimentally and by modeling. At low injection velocities SiC particles react with the molten aluminum alloy. Only a small fraction of SiC remains in the microstructure, which contains large amounts of particles of the reaction products Al₄SiC₄ and Si dispersed in the α-Al + Si eutectic matrix. By contrast, at high injection velocities chemical reactions between SiC and molten aluminum are almost entirely suppressed and the resulting microstructure consists only of SiC particles dispersed in the matrix. To investigate whether this behavior could be explained by the different temperatures reached by the injected particles as they fly through the laser beam, a physical-mathematical model describing the interaction between the laser beam and the powder stream in the off-axis blown powder laser cladding process was developed and applied to calculate the temperature attained by the powder particles as a result of their interaction with an Nd:YAG laser beam (λ = 1.06 µm). At an injection velocity of 1 m/s the maximum temperature attained by SiC and Al-12Si particles is 3150 and 180 ºC, respectively. This result demonstrates that particle injection velocity is a major parameter affecting the microstructure of coatings produced by laser cladding, and must be carefully controlled.     

Characteristic reaction products in the AZ91/SiC composite fabricated by pressureless infiltration technique

Since the spontaneous infiltration of molten AZ91 Mg alloy into a powder bed containing SiC particles occurred at 700 °C for 1 h under a nitrogen atmosphere, it was possible to fabricate Mg alloy composites reinforced with SiC particles. Since the fabrication conditions (e.g. temperature, time, and atmosphere) of the composite are different from those of the other fabrication route, reaction products formed during the composite fabrication were investigated in detail using field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HRTEM). From the analysis results, we could identify the formation of MgAl₂O₄ and AlN, as well as MgO in fabricated composite.     

Carbothermic reduction of chromite fluxed with aluminum spent potlining

Aluminum spent potlining (SPL) was employed as both the fluxing agent and a source of carbonaceous reductant for the carbothermic reduction of chromite, aiming to allow effective separation of alloy from the slag component. The experimental results show that the carbonaceous component of the SPL is more reactive towards chromite reduction compared to graphite. The formation of refractory spinel (MgAl₂O₄) on chromite particles hinders further reduction and alloy growth. The slag-making components of the SPL (e.g. nepheline and NaF) form molten slags at low temperatures (～1300 °C) and partly dissolve the refractory spinel as well as the chromite. Destruction of the spinel layer with enhanced mass transfer greatly improves the alloy growth, which can be further promoted by reduction at a higher temperature (e.g. 1500 °C). Ferrochrome alloy particles grow large enough at 1500 °C in the presence of SPL, allowing effective separation from the slag component using elutriation separation.     

铝基碳化硅复合材料电火花高效加工仿真研究

为探究电火花加工铝基碳化硅复合材料的单脉冲放电蚀除过程,建立了铝基体与碳化硅颗粒的材料抛出流固耦合动力学模型,研究了放电区域熔融铝基体金属夹带固态碳化硅颗粒的高速抛出微观过程,并开展了电火花高效加工与传统电火花加工效率对比仿真。结果表明:离放电中心点较近的碳化硅材料以熔融态抛离基体,而远离放电中心位置的碳化硅以固态颗粒形式夹杂在熔融材料中得以抛出;同时,铝基碳化硅复合材料采用电火花高效加工方法时,加工效率较传统电火花加工有显著提升。     

Anomalous reheating behavior of SiCp/Al composite with high volume fraction reinforcement

The reheating behavior of 50 vol.% SiCp/Al squeeze casting composite was investigated at temperatures ranging from 600°C to 900°C using XRD and SEM techniques from the microstructural point of view. It was found that SiCp/Al composite could hold its original shape while being reheated at temperatures elevated even far above the melting temperature of pure Al. The high volume fraction of SiC reinforcement, which would restrict the fluidity of molten Al matrix and the reconfiguration of SiC particles during the reheating of SiCp/Al composite, was thought to be responsible for the “remelting resistance” of the SiCp/Al composite. The extent of the reaction between the SiC particles and molten Al was found to increase with increased reheating temperature. From the viewpoint of controlling the formation of aluminum carbide, reheating temperature either for recycling or for remelting processing of the SiCp/Al composite, a temperature lower than 750°C would be better. Despite its being unfavorable to remelting or recycling processing, the remelting resistance of the SiCp/Al composite with high volume fraction reinforcement is attractive for thermal function and high temperature applications.     

Effect of Mg content on the dimensional stability and tensile properties of heat treated Al-Si-Cu (319) type alloys

The present study was performed on A319.2 aluminum alloy containing 6.2% Si, 3.46% Cu, 0.35% Fe, 0.1% Mg. Small amounts of additives were added to the molten metal as follows: 0.5% Mg, (0.5%Mg + 0.03% Sr), (0.5%Mg + 0.03% Sr + 0.02% TiB₂). The fluidity of the molten metal as a function of temperature in the range 620–740 °C was measured using the Ragone testing technique. Two solution treatments were applied to test bars prepared from these alloy compositions: 6–8 h at 470 °C, and 6–8 h at 505 °C. In both cases, the test bars were quenched in hot water (60 °C), followed by immediate ageing for 5 h at 180 °C. The results reveal that Sr slightly improves the fluidity of the molten metal (～12%) at 720 °C. The addition of Mg leads to a noticeable increase in the alloy length (～2%) when the solution temperature is above 500 °C. At this temperature, incipient melting of Al₅Mg₈Si₆Cu₂ and Al₂Cu phase particles located at the grain boundaries was significant. Ageing at 180 °C contributes significantly to the alloy strength without much change in the dimension. The magnitude of the increase in alloy strength is strongly related to the solution temperature. Solution treatment for 8–10 h at 500 °C may be recommended.     

Enhancing wettability of SiC in semisolid A356 aluminium matrix composites

Abstract

Stir casting plus cooling plate technique has been used for the fabrication of Al matrix composites based on alloy 356. Improvement of the wettability of SiC particles was carried out, employing the oxidisation of SiC particles, the use of wetting agents by adding magnesium into the matrix and the coating of SiC particles using a sol–gel technique. The introduction of SiC particles into partially solidified alloy with high viscosity prevents the particles from floating and agglomerating. Unoxidised SiC particles are mostly detached from the Al matrix during the grinding suggesting poor adhesion and poor wettability between the matrix and the particles. Oxidised SiC particles and sol–gel silica coated SiC particles indicate good binding between composite and matrix. The use of magnesium promoted wettability of SiC with A356 alloy. The eutectic silicon phase formed on the surface of SiC particles during solidification may be due to nucleation effects provided by the particles.     

Particle weakening in superplastic SiC/2124 Al composites at high temperature

High-strain-rate superplastic behavior of powder-metallurgy-processed 2124 Al matrix alloy and 10%, 20% and 30% SiC particulate reinforced 2124 Al composites were investigated over the temperature range from 370°C to 565°C, and the strain rate range from 10⁻⁴/s to 1/s. The true activation energy for the plastic flow after threshold stress compensation was close to that for lattice diffusion in aluminum for the 2124 Al alloy, while the activation energies for the 2124 composites were considerably higher than those for the unreinforced alloy, increasing with an increase in the volume fraction of SiC. The strength of the 2124 Al composites is lower than the strength of the 2124 Al alloy at high temperatures. The strength differential between the unreinforced and reinforced 2124 Al alloys is a function of temperature and is seen to decrease systematically with decrease in temperature and virtually vanishes at 460°C. Particle weakening is discussed in the light of load transfer effect, interphase diffusion, dissolution of second phase particles into matrix and the presence of liquid phase. It is proposed that interphase weakening, possibly with some liquid formation, is the principal factor contributing to the results obtained. Interphase and boundary sliding is believed to be the rate-controlling process in plastic flow of the SiC/2124 Al composites.     

浸渗法制备高铬铸铁/TiC-SiC复合材料及微观组织

采用小颗粒TiC包覆SiC陶瓷颗粒,在惰性气体保护下选用无压浸渗方法制备了高铬铸铁/TiC-SiC复合材料;利用SEM/EDX观察和分析了液态铸铁在SiC预制体中的浸渗情况、组织特征和成分分布;结合高铬铸铁/Ti-SiC复合材料的组织特点和浸渗行为特点,分析了TiC粉体对浸渗行为和复合材料组织的影响。观察结果表明,当TiC加入量≤10%(质量分数,下同)时,Fe/Cr合金无法润湿SiC颗粒,而当加入量≥20%时,Fe/Cr合金和预制体之间润湿性得到改善,增加TiC含量更有利于Fe/Cr合金浸渗;基体中大尺寸SiC颗粒消失,出现了尺寸接近毫米级的条状单质碳,这与高铬铸铁/Ti-SiC复合材料的组织差异较大。对比两种复合材料组织发现,添加Ti粉末在金属液中可与C结合生成TiC,而添加的TiC颗粒在组织中呈鹅卵石状,边缘圆润,出现金属液与陶瓷颗粒之间的互溶。在浸渗过程中,添加TiC和Ti与浸渗金属发生的反应不同,且高质量分数的TiC对金属液浸渗过程有明显的促进作用。     

Nano-SiCP particles distribution and mechanical properties of Al-matrix composites prepared by stir casting and ultrasonic treatment

Nano-ceramic particles are generally difficult to add into molten metal because of poor wettability. Nano-SiC_Particles reinforced A356 aluminum alloy composites were prepared by a new complex process, i.e., a molten-metal process combined with high energy ball milling and ultrasonic vibration methods. The nano particles were β-SiC_P with an average diameter of 40 nm, and pre-oxidized at about 850 °C to form an oxide layer with a thickness of approximately 3 nm. The mm-sized composite granules containing nano-SiC_P were fi rstly produced by milling the mixture of oxidized nano-SiC_P and pure Al powders, and then were remelted in the matrix-metal melt with mechanical stirring and treated by ultrasonic vibration to prepare the composite. SEM analysis results show that the nano-SiC_P articles are distributed uniformly in the matrix and no serious agglomeration is observed. The tensile strength and elongation of the composite with 2 wt.% nano-SiC_P in as-cast state are 226 MPa and 5.5%, improved by 20% and 44%, respectively, compared with the A356 alloy.     

真空压力浸渗制备SiCp/AZ91复合材料的显微组织、力学性能和磨损行为

采用真空压力浸透法制备SiC_p/AZ91复合材料,研究其显微组织、力学性能和耐磨性。结果表明,SiC颗粒均匀分布于金属基体中,并与基体界面结合良好。Mg₁₇Al₁₂相在SiC颗粒附近优先析出,SiC与AZ91基体的热膨胀系数失配导致高密度位错的产生,加速基体的时效析出。与AZ91合金相比,SiC颗粒的加入提高了复合材料的硬度和抗压强度,这主要是由于载荷传递强化和晶粒细化强化机制。此外,由于SiC具有优异的耐磨性,在磨损过程中形成稳定的支撑面保护基体。     

Oxidation of ZC63 Mg alloys reinforced with SiC particles between 390 °C and 500 °C in air

The ZC63 magnesium alloys reinforced with 10 wt.% of SiC particles with an average particle size of 50 μm were cast. The fabricated SiC_p/ZC63 composite consisted of an α-Mg matrix, unreacted α-SiC particles, and an intergranularly formed CuMgZn compound. It was oxidized at 390 °C to 500 °C up to 5 h in air. The oxide scales were thin and compact below 430 °C, but became porous and loose above 450 °C. They consisted primarily of MgO and a small amount of Mg₃N₂. SiC particles were stable over the temperature range explored.     

Ti-coated SiC particle reinforced sintered Fe-Cu-Sn alloy

Ti-coated SiC particles were developed to improve the wear resistance of Fe-Cu-Sn alloy metal matrices designed for diamond tools. The phase structure of the Ti-coated SiC particles was investigated by X-ray diffraction. Ti coating on SiC was composed of Ti₅Si₃, TiC, and Ti. Excellent interfacial bonding between SiC and the matrix was realized. The SiC/iron alloy composites, prepared by hot pressing at 820 °C, were studied by wear and bending strength tests, and scanning electron microscope. For the composites reinforced by uncoated SiC particles, the wear resistance was improved, but the bending strength decreased. The composites with Ti-coated SiC particles outperformed the composites with uncoated SiC particles in both wear resistance and bending strength tests.     

Wear behavior of AI-Si alloy matrix composites reinforced by γ-Al2O3 decomposed from AACH

The Al-Si alloy matrix composite reinforced by γ-Al2O3 particles was produced by adding NH4AlO（OH）HCO3（AACH） into molten Al-Si alloy at 850℃. During stirring γ-Al2O3 particles are formed by the decomposing reaction of AACH. It is found that the γ-Al2O3 particles distribute more uniformly in the matrix by adding AACH than by adding γ-Al2O3 directly. The wear tests show that the volume loss of the unreinforced Al-Si alloy matrix is about 3 times larger than that of the γ-Al2O3 reinforced composites and that of the composites fabricated by adding γ-Al2O3 is larger than that by adding AACH.     

Mechanism of laser beam welding for SiCp／6063Al composite

The laser beam welding technique was used to process SiC particles/6063A1 alloy matrix composite, the influence of laser power and welding speed on the properties of joint was studied. Decreasing the laser beam power with same welding speed can make the quantity and size of A14C3 decreased, and the interactive mechanism of the reinforcing particles and the matrix in the joint and the causes for joint strength reduction were analyzed.Increasing welding speed properly can improve the distribution of energy and restrain the interfacial reaction in the molten pool, and measures for improving were proposed.     

The Effect of Plasma Spraying on the Microstructure and Aging Kinetics of the Al-Si Matrix Alloy and Al-Si/SiC Composites

The Al-Si (LM 13)-based matrix alloy reinforced with SiC particles containing 10, 20, and 30 vol.% SiC particles were spray-formed onto Al-Si substrates. The sprayed samples were directly subjected to a standard aging treatment (T551). From the experiments, it was observed that the high rate of solidification resulted in very fine silicon particles which were observed as continuous islands in the matrix and each island exhibited several very fine silicon crystals. Analysis showed that plasma-spraying caused an increased solid solubility of the silicon in the aluminum matrix. DSC measurements in the permanent mold-cast Al-Si matrix alloy and plasma-sprayed Al-Si matrix alloy showed that plasma-spraying causes an increase in the amount of GP-zone formation owing to the very high rate solidification after plasma-spraying. In the plasma-sprayed Al-Si/SiC composites GP zones were suppressed, since particle-matrix interfaces act as a sink for vacancies during quenching from high plasma process temperature. Introduction of SiC particles to the Al-Si age-hardenable alloy resulted in a decrease in the time required to reach plateau matrix hardness owing to acceleration of aging kinetics by ceramic SiC particles.     

Influence of reinforcement grade and matrix composition on corrosion resistance of cast aluminium matrix composites (A3xx.x/SiCp) in a humid environment

A study of the influence of the silicon carbide (SiC_p) proportion and the matrix concentration of four aluminium metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) exposed to high relative humid environment was carried out under simulation in a climatic chamber. The matrix of A360/SiC/xxp composites was virtually free of copper while the A380/SiC/xxp matrix contained 3.13‐3.45wt% Cu and 1.39‐1.44wt% Ni. The kinetics of the corrosion process was studied on the basis of gravimetric tests. The nature of corrosion products was analysed by Scanning Electron Microscopy (SEM) and Low Angle X‐Ray Diffraction (XRD) before and after accelerated testing to determine the influence of microstructural changes on corrosion behaviour during exposure to the corrosive environment. The corrosion damage to Al/SiCp composites was low at 80% Relative Humidity (RH) and increased with temperature, SiCp proportion, relative humidity and Cu matrix concentration. The main attack nucleation sites were the interface region between the matrix and the reinforcement particles. The corrosion process was influenced more by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement.     

Sand Abrasive Wear Behavior of Hot Forged Al 6061-TiO2 Composites

Nickel-coated TiO₂ particulate reinforced Al6061 matrix composites developed using the vortex technique were hot forged at a temperature of 500 °C. A constant deformation ratio of 6:1 was adopted. Hot forged Al6061 alloy and Al6061-TiO₂ composites were then subjected to heat treatment by solutionizing at a temperature of 530 °C for duration of 2 h followed by ice quenching. Both natural and artificial aging at 175 °C were performed on the quenched samples from 2 to 8 h duration in steps of 2. Microstructure, microhardness, and dry sand abrasive wear behavior of both matrix alloy and developed composites in both as-forged and heat-treated conditions have been evaluated. Worn surface studies have been carried out using scanning electron microscope. Results have revealed that nickel-coated TiO₂ particles are uniformly distributed through out the matrix alloy. Microhardness of Al6061-TiO₂ composites increases with increase in percentage of reinforcement. Heat-treated forged alloy and its composites possesses higher hardness when compared with the forged composites. Forged Al6061-TiO₂ composites exhibited lower abrasive wear loss when compared with the forged matrix alloy. Heat treatment has a profound effect on the abrasive wear resistance of both as-forged Al6061 alloy and Al6061-TiO₂ composites.     

Fluidity of Al based metal matrix composites containing Al2O3 and SiC particles

Abstract

The flow behaviour of aluminium alloy matrix composites containing Al₂O₃ and SiC particles is studied. A357 aluminium alloy was the matrix alloy common to both metal matrix composites (MMCs). Reinforcing particles were similar in shape and size (40 μm). Both MMCs were made by the stir casting process using parameters optimised so far as possible. The flowability of the MMCs was studied by measuring the fluidity of strips cast in a permanent mould. The results showed that the fluidity of both MMCs appeared to be reduced by increasing percentage addition of particles and further reduced by increasing times and temperature. It is proposed that much of this behaviour is not the result of the added reinforcing particles but the result of oxide films necessarily entrained by the stir casting process. The agglomeration of additions commonly seen in particulate MMCs is also attributed to the entrainment of clusters of additions as they enter the liquid through the surface oxide film.