Fabrication and characterization of Al356/SiCp semisolid composites by injecting SiCp containing composite powders

Al356/5 vol.% SiC_p cast composites were fabricated by the injection of reinforcement particles into the melt in three different forms, i.e. as untreated SiC_p, milled particulate Al-SiC_p composite powder, and milled Al-SiC_p-Mg composite powder. The resultant composite slurries were then cast in the semisolid temperature range of the alloy, upon which the effects of the type of injected powder on the distribution and incorporation of the reinforcement particles, along with the hardness of the cast composites, were investigated. Injection of milled composite powders resulted in considerable improvement in SiC_p wetting as well as the incorporation and distribution of SiC_p in the Al356 matrix alloy. Al356/5 vol.% SiC_p composite with well dispersed reinforcement particles of less than 3 μm average diameter was successfully produced by injecting Al-SiC_p-Mg composite powder into the melt. The best microstructural characteristics in terms of the reinforcement incorporation and distribution, and the highest hardness value of the cast composites, were achieved when magnesium was added through the injected composite powder and not directly into the melt.     

Microstructures and mechanical properties of Al 2519 matrix composites reinforced with Ti-coated SiC particles

Ti-coated SiC_p particles were developed by vacuum evaporation with Ti to improve the interfacial bonding of SiC_p/Al composites. Ti-coated SiC particles and uncoated SiC particles reinforced Al 2519 matrix composites were prepared by hot pressing, hot extrusion and heat treatment. The influence of Ti coating on microstructure and mechanical properties of the composites was analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that the densely deposited Ti coating reacts with SiC particles to form TiC and Ti₅Si₃ phases at the interface. Ti-coated SiC particle reinforced composite exhibits uniformity and compactness compared to the composite reinforced with uncoated SiC particles. The microstructure, relative density and mechanical properties of the composite are significantly improved. When the volume fraction is 15%, the hardness, fracture strain and tensile strength of the SiC_p reinforced Al 2519 composite after Ti plating are optimized, which are HB 138.5, 4.02% and 455 MPa, respectively.     

SiCp/Al复合材料与Fe36Ni合金超声波钎焊

利用超声波钎焊方法使用ZnAlSi钎料实现了Fe36Ni合金与45%SiC_p/2024Al和55%SiC_p/A356两种复合材料的连接,并得到由SiC颗粒增强的复合焊缝.通过扫描电镜、能谱等方法对焊缝的微观结构以及断口形貌进行了观察,对接头的压剪强度进行了测试,分析了Fe36Ni与两种复合材料钎焊接头微观组织和接头强度的差异.结果表明,在Fe36Ni与两种复合材料的钎缝中,钎料与两侧母材界面均形成良好的冶金结合,SiC颗粒均匀分布于焊缝中.Fe36Ni与45%SiC_p/2024Al的接头抗剪强度为110~145 MPa,Fe36Ni与55%SiC_p/A356的接头抗剪强度为75~85 MPa.Fe36Ni与45%SiC_p/2024Al的接头断裂位置为钎缝中,而Fe36Ni与55%SiC_p/A356的接头断裂位置位于Fe36Ni与钎料的界面上.     

Effects of nano-SiCp content on microstructure and mechanical properties of SiCp/A356 composites assisted with ultrasonic treatment

nano-SiC_p/A356 composites with different nano-SiC_p contents were prepared by squeeze casting after ultrasonic treatment (UT). The effects of SiC_p content on the microstructure and mechanical properties of the nanocomposites were investigated. The results show that with the addition of nano-SiC_p, the microstructure of nanocomposites is obviously refined, the morphology of the α(Al) grains transforms from coarse dendrites to rosette crystals, and long acicular eutectic Si phases are shortened and rounded. The mechanical properties of 0.5%, 1% and 2% (mass fraction) SiC_p/A356 nanocomposites are improved continuously with the increase of nano-SiC_p content. Especially, when the SiC_p content is 2%, the tensile strength, yield strength and elongation are 259 MPa, 144 MPa and 5.3%, which are increased by 19%, 69% and 15%, respectively, compared with those of the matrix alloy. The improvement of strength is attributed to mechanisms of Hall-Petch strengthening and Orowan strengthening.     

Production of High-Strength Al/Al2O3/WC Composite by Accumulative Roll Bonding

In this study, Al/Al₂O₃/WC composites were fabricated via the accumulative roll bonding (ARB) process. Furthermore, the microstructure evolution, mechanical properties, and deformation texture of the composite samples were reported. The results illustrated that when the number of cycles was increased, the distribution of particles in the aluminum matrix improved, and the particles became finer. The microstructure of the fabricated composites after eight cycles of the ARB process showed an excellent distribution of reinforcement particles in the aluminum matrix. Elongated ultrafine grains were formed in the ARB-processed specimens of the Al/Al₂O₃/WC composite. It was observed that as the strain increased with the number of cycles, the tensile strength, microhardness, and elongation of produced composites increased as well. The results indicated that after ARB process, the overall texture intensity increases and a different-strong texture develops. The main textural component is the Rotated Cube component.     

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。     

Microstructure and Mechanical Properties of Al356/SiCp Cast Composites Fabricated by a Novel Technique

In this study, SiC_p containing composite powders were used as the reinforcement carrier media for manufacturing cast Al356/5 vol.% SiC_p composites. Untreated SiC_p, milled particulate Al-SiC_p composite powder, and milled particulate Al-SiC_p-Mg composite powder were injected into Al356 melt. The resultant composite slurries were then cast from either a fully liquid state (stir casting) or semisolid state (compocasting). The results revealed that by injection of composite powders, the uniformity of the SiC_p in the Al356 matrix was greatly improved, the particle-free zones in the matrix were disappeared, the SiC particles became smaller, the porosity was decreased, and the matrix microstructure became finer. Compocasting changed the matrix dendritic microstructure to a finer non-dendritic one and also slightly improved the distribution of the SiC_p. Simultaneous utilization of Al-SiC_p-Mg composite powder and compocasting method increased the macro- and micro-hardness, impact energy, bending strength, and bending strain of Al356/SiC_p composite by 35, 63, 20, 20, and 40%, respectively, as compared with those of the composite fabricated by injection of untreated SiC_p and stir casting process.     

SiCp/Al复合材料电子束焊接接头组织及性能

对SiCp/Al复合材料自身进行电子束焊接,研究了其接头成形、焊缝组织、热影响区组织及接头力学性能.结果表明,SiCp/Al复合材料自身直接电子束焊接时,接头的主要缺陷是焊缝成形差、易形成两侧堆积颗粒物的凹槽;焊缝组织中存在界面反应产生的灰白色初生硅、深灰色针状相Al4C3以及Al-Si共晶中的浅灰色针状共晶硅,形成脆性区,拉伸断裂位置便在此处,断裂为脆性断裂.熔合区附近硬度较高,与焊缝区组织及硬度差异较大.接头的最高强度为73 MPa,仅占母材平均抗拉强度的41％.     

Fabrication and characterization of cast magnesium matrix composites by vacuum stir casting process

A vacuum stir casting process is developed to produce SiC_p reinforced cast magnesium matrix composites. This process can eliminate the entrapment of external gas onto melt and oxidation of magnesium during stirring synthesis. Two composites with Mg-Al9Zn and Mg-Zn5Zr alloys as matrices and 15 vol.% SiC particles as reinforcement are obtained. The microstructure and mechanical properties of the composites and the unreinforced alloys in as-cast and heat treatment conditions are analyzed and evaluated. In 15 vol.% SiC_p reinforced Mg-Al9Zn alloy-based composite (Mg-Al9Zn/15SiC_p), SiC particles distribute homogenously in the matrix and are well bonded with magnesium. In 15 vol.% SiC_p reinforced Mg-Zn5Zr alloy-based composite (Mg-Zn5Zr/15SiC_p), some agglomerations of SiC particles can be seen in the microstructure. In the same stirring process conditions, SiC reinforcement is more easily wetted by magnesium in the Mg-Al9Zn melt than in the Mg-Zn5Zr melt. The significant improvement in yield strength and elastic modulus for two composites has been achieved, especially for the Mg-Al9Zn/15SiC_p composite in which yield strength and elastic modulus increase 112 and 33%, respectively, over the unreinforced alloy, and increase 24 and 21%, respectively, for the Mg-Zn5Zr/15SiC_p composite. The strain-hardening behaviors of the two composites and their matrix alloys were analyzed based on the microstructure characteristics of the materials.     

Thermal conductive properties of Ni-P electroless plated SiCp/Al composite electronic packaging material

Electroless plated SiC_p/Al composites with a high thermal conductivity are required for electronic packaging application. In this paper, in-plane thermal conductive properties of SiC_p/Al composites with and without electroless plated Ni-P coatings are compared, and influence of various characteristics of Ni-P coatings are investigated. It is found that in addition to thickness of the coatings, phosphorus concentration and microstructure of the plated layers also influence the thermal conductive properties of plated composites. Based on the results, it is suggested that a low phosphorus concentration and a properly tailored crystalline microstructure of the Ni-P coatings, together with a reasonable choice of coating thickness, may contribute to optimization of thermal conductive properties of the composite material.     

SiC_p/2024与2219铝合金电子束焊接

分别采用电子束对中焊、偏束焊技术,研究了Si C颗粒增强铝基复合材料Si Cp/2024与2219铝合金的接头组织及力学性能.结果表明,对中焊时接头易出现Si C增强相的偏聚,同时发生严重的界面反应,生成大量脆性相Al4C3,接头抗拉强度最高为104 MPa.采用偏束焊工艺可以很好地抑制界面反应,通常只在焊缝上部与Si Cp/Al热影响区上部生成少量脆性相Al4C3,接头抗拉强度最高可达131 MPa.试件均断裂在母材界面反应层上,且为明显的脆性断裂.不同工艺下接头横截面硬度分布存在突变区,该区域在Si Cp/2024熔合区附近,该处脆性相Al4C3的生成导致硬度升高.     

Comparison of the Microstructure and Mechanical Properties of As-Cast A356/SiC MMC Processed by ARB and CAR Methods

Accumulative roll bonding (ARB) and continual annealing and roll-bonding (CAR) processes were used in this study for improving the microstructure and mechanical properties of the A356/10?vol.% SiC metal matrix composite (MMC) produced by semi-solid metal processing (SSM). The results showed that using the ARB and CAR processes led to the following points: (a) the uniformity of the silicon and silicon carbide in the aluminum matrix improved, (b) the Si particles became finer and more spheroidal in appearance, (c) the porosity disappeared, (d) the bonding quality between the reinforcement and the matrix improved, (e) the particle-free zone disappeared, and therefore (f) the tensile strength (TS), elongation, and formability index of the MMC samples improved. However, it was found that the CAR process is a better method for improvement of microstructure and mechanical properties of as-cast MMC compared to ARB process.     

Production and mechanical properties of nano SiC particle reinforced Ti–6Al–4V matrix composite

Different mass fractions (0, 5%, 10%, and 15%) of the synthesized nano SiC particles reinforced Ti–6Al–4V (Ti64) alloy metal matrix composites (MMCs) were successfully fabricated by the powder metallurgy method. The effects of addition of SiC particle on the mechanical properties of the composites such as hardness and compressive strength were investigated. The optimum density (93.33%) was obtained at the compaction pressure of 6.035 MPa. Scanning electron microscopic (SEM) observations of the microstructures revealed that the wettability and the bonding force were improved in Ti64 alloy/5% nano SiC_p composites. The effect of nano SiC_p content in Ti64 alloy/SiC_p matrix composite on phase formation was investigated by X-ray diffraction. The correlation between mechanical parameter and phase formation was analyzed. The new phase of brittle interfaced reaction formed in the 10% and 15% SiC_p composite specimens and resulted in no beneficial effect on the strength and hardness. The compressive strength and hardness of Ti64 alloy/5% nano SiC_p MMCs showed higher values. Hence, 5% SiC_p can be considered to be the optimal replacement content for the composite.     

Effect of thermal cycling on the expansion behavior of Al/SiCp composite

The coefficient of thermal expansion (CTE) and accumulated plastic strain of the pure aluminum matrix composite containing 50% SiC particles (Al/SiC_p) during thermal cycling (within temperature range 298–573 K) were investigated. The composite was produced by infiltrating liquid aluminum into a preform made by SiC particles with an average diameter of 14 μm. Experiment results showed that the relationship between the CTE of Al/SiC_p and temperature is nonlinear; CTE could reach a maximum value at about 530 K. The theoretical accumulated plastic strain of Al/SiC_p composites during thermal cycling has also been calculated and compared with the experimental results.     

热处理对SiCp/6061Al基复合材料等离子弧焊接头性能的影响

热处理对SiCp/6061Al基复合材料等离子弧原位焊接接头组织与性能的影响较为明显,固溶处理 时效与退火相比,前者对接头的改善作用更佳.经500 ℃固溶处理2 h 12 h时效热处理后,接头组织得到良好的改善,细长的Al3Ti相变为短小棒状,消除了晶间偏析,组织更加均匀;热影响区组织中晶粒均得到比较明显的细化,比较接近母材晶粒的大小,焊接接头强度较未热处理时有了较大提高,达到245 MPa.     

Microstructural evolution and its effects on mechanical properties of spray deposited SiCp/8009Al composites during secondary processing

15% (volume fraction) SiC_p/8009Al metal matrix composites(MMCs) prepared by spray co-deposition were hot-extruded and rolled to investigate the effects of porosity and local SiC_p clusters on mechanical properties. The microstructures were examined by using optical microscopy(OM), scanning electron microscopy(SEM), X-ray diffractometry(XRD) and transmission electron microscopy(TEM). The mechanical properties were measured by tensile testing. The experimental results show that lamellar structure is composed of pores and SiC_p clusters and can be improved by secondary processing, enhancing mechanical properties. The main strengthening mechanism and fracture behavior of MMCs were discussed too.     

中间层对高体积分数SiCp/Al复合材料真空钎焊的影响

采用铜箔、Al-Si-Mg及Al-Si-Mg/Cu/Al-Si-Mg(简称ACA)3种不同中间层对高体积分数45%SiC_p/Al复合材料进行真空钎焊连接研究.通过SEM,EDS及XRD等方法对钎缝的微观结构及界面组织进行了分析,研究了中间层种类对钎焊接头微观结构、界面组织以及连接强度的影响,阐明了不同中间层钎焊连接45%SiC_p/Al复合材料的界面形成过程及接头断裂机制.结果表明,ACA中间层兼具了铜和Al-Si-Mg钎料的优点,可降低钎料的液相线,增加其流动性,通过Cu原子优先在铝合金基体与其氧化膜的界面处扩散发生共晶反应,增强钎料的去膜作用,从而实现高体积分数45%SiC_p/Al复合材料的高质量连接.     

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.     

Effect of thermal-cooling cycle treatment on thermal expansion behavior of particulate reinforced aluminum matrix composites

Two micron SiC particles with angular and spherical shape and the sub-micron Al2O3 particles with spherical shape were introduced to reinforce 6061 aluminium by squeeze casting technology.Microstructures and effect of thermal-cooling cycle treatment(TCCT) on the thermal expansion behaviors of three composites were investigated.The results show that the composites are free of porosity and SiC/Al2O3 particles are distributed uniformly.Inflections at about 300 °C are observed in coefficient of thermal expansion(CTE) versus temperature curves of two SiCp/Al composites,and this characteristic is not affected by TCCT.The TCCT has significant effect on thermal expansion behavior of SiCp/Al composites and CTE of them after 3 cycles is lower than that of 1 or 5 cycles.However,no inflection is observed in Al2O3p/Al composite,while TCCT has effect on CTE of Al2O3p/Al composite.These results should be due to different relaxation behavior of internal stress in three composites.     

Effect of forging temperature on the microstructures and mechanical properties of the SiCp/AZ91 magnesium matrix composite

In this paper, 10 vol. pct SiC_p/AZ91 magnesium matrix composite was fabricated by stir casting technology. The ingots were forged at temperatures of 320, 370 and 420 ℃, respectively. XRD, OM and SEM were used to characterize microstructure of the composites. It was shown that the clusters of particles in the as-cast composite were largely eliminated, and that the tensile strength was improved obviously.