CNTs/SiC_p/AZ91D镁基复合材料的力学性能研究

采用搅拌铸造法制备了碳纳米管(CNTs)与碳化硅颗粒(SiC_p)增强AZ91D镁基复合材料,对复合材料的力学性能进行了测试,对其显微组织进行观察和分析。结果表明:增强相使复合材料的晶粒细化,与基体合金相比,当CNTs、SiC_p含量分别是1.1 vol%、3 vol%时,复合材料的弹性模量为70.8 GPa,比基体提高了57.3%。当SiC_p含量一定时,复合材料的延伸率随CNTs含量的增加先增加后减小;对于只含镀镍CNTs的复合材料而言,当CNTs的体积分数为1.1%时,复合材料的延伸率最大,最高值达到了13.81,比基体材料提高了近60.6%,而1.1 vol%CNTs/2 vol%SiC_p/Mg的延展率比基体略有降低。当CNT体积分数一定,复合材料的延伸率均随SiC_p含量的增加而减小。     

界面改性对SiC_p/Cu复合材料热物理性能的影响

采用热压烧结法成功制备SiC_p/Cu复合材料。采用溶胶-凝胶工艺在SiC颗粒表面制备Mo涂层,研究Mo界面阻挡层对复合材料热物理性能的影响。结果表明:过氧钼酸溶胶-凝胶体系能够在SiC颗粒表面包覆连续性、均匀性较好的MoO_3涂层,最佳工艺配比为SiC∶MoO_3=5∶1(质量比)、过氧化氢∶乙醇=1∶1(体积比),SiC表面丙酮和氢氟酸预清洗处理有利于MoO_3涂层的沉积生长。MoO_3在540℃第一步氢气还原后转变为MoO_2,MoO_2在940℃第二步氢气还原后完全转变为Mo,Mo涂层包覆致密完整。热压烧结SiC_p/Cu复合材料微观组织致密均匀,且相比原始SiC颗粒增强的SiC_p/Cu,经溶胶-凝胶法界面改性处理的SiC_p/Cu复合材料热导率明显提高,SiC体积分数约为50%时,SiC_p/Cu复合材料热导率达到214.16W·m~(-1)·K~(-1)。     

粉末冶金法制备SiC_p/Al_2W_3O_(12)/Al复合材料及其热膨胀性能

通过添加适量的Al_2W_3O_(12)负热膨胀粉体来优化碳化硅颗粒增强铝基(SiC_p/Al)复合材料的热膨胀系数。实验采用固相法制备负热膨胀性能的Al_2W_3O_(12)粉体,并按10%,20%,30%的体积比添加至SiC_p/Al复合粉体中,利用粉末冶金工艺制备SiC_p/Al_2W_3O_(12)/Al复合材料。实验结果表明:制备的复合材料组织分布均匀,致密度良好。室温到200℃内,在Al基体质量分数不变的前提下,Al_2W_3O_(12)的加入有效降低了复合材料的热膨胀系数。     

高体积分数SiCp/A356复合材料的显微组织和电导率

铝基复合材料在电子封装领域存在着潜在的应用前景。为获得高体积分数的铝基复合材料,利用压力浸渗法制备了高体积分数SiC颗粒增强A356复合材料(SiC_p/A356),通过金相显微镜、XRD、SEM和EDS等分析手段对其物相、显微结构和电导率进行了表征。结果表明:用该方法制备的SiC_p/A356复合材料组织致密,颗粒分布均匀,界面结合性能较好;SiC增强颗粒与A356基体界面反应控制良好,仅有少量Al4C3脆性相生成。SiC粉体经颗粒表面氧化处理在其表面生成一层SiO_2薄膜,虽抑制了界面反应的发生,但也使复合材料的收缩减小,电阻率增大,导电性能变差。     

超声外场对SiCp/7085复合材料界面及拉伸性能的影响

为研究超声辅助制备工艺对SiC_p/7085复合材料界面结合及拉伸性能的影响,用机械搅拌、机械搅拌+超声施振、超声施振3种工艺制备体积分数为10%的SiC_p/7085复合材料.采用扫描电子显微镜(SEM)、能谱(EDS)研究各工艺对SiC_p/7085复合材料的界面微观组织和拉伸性能的影响.实验结果表明:机械搅拌工艺促进大颗粒(80μm)与熔体结合,但产生了粗大Al4C3界面产物包裹层,且难改善小颗粒(37μm)与熔体界面结合差的问题;超声施振能促进界面反应,生成尺寸细小、排列规整、紧密的Mg O、Mg Al2O4界面强化相覆盖层,有效改善小颗粒与熔体界面结合;相比于7085铝合金,机械搅拌不能改善SiC_p/7085复合材料拉伸性能,而超声施振的加入能显著提升材料拉伸性能.     

Sn3.0Ag0.5Cu3.0Bi钎料对化学镀镍SiCp/6063Al复合材料真空钎焊接头组织和性能的影响

采用Sn3.0Ag0.5Cu3.0Bi软钎料对镀镍后的两种不同体积比SiC_p/6063Al复合材料进行真空钎焊。通过SEM、剪切试验等方法分析了化学镀镍后SiC_p/6063Al复合材料真空钎焊接头的显微组织以及保温时间对接头性能的影响。结果表明:两种不同体积比SiC_p/6063Al复合材料真空钎焊后的焊缝组织致密,钎料对镀镍复合材料的润湿性良好;在270℃、保温35min的钎焊工艺下,钎焊接头的剪切强度最大值为38.3 MPa;钎料中的Sn、Cu元素能够与复合材料表面的Ni层发生化学反应,实现钎料与母材的冶金结合;镀镍后SiC_p/6063Al复合材料真空钎焊接头断裂形式为韧性断裂为主的混合断裂,断裂主要发生在钎料内部,部分发生在镀镍层与钎料的结合处。     

不同体积分数SiC_p/Al复合材料薄壁板的变形仿真

应用ABAQUS软件对SiC_p/Al复合材料薄壁板的变形进行仿真研究,得出了载荷施加位置、SiC颗粒体积分数对SiC_p/Al复合材料薄壁板变形及应力的影响规律。结果表明:随载荷施加位置沿约束方向从薄壁板的中间向端部移动,薄壁板的最大变形和最大应力增加趋势越来越明显;随着载荷施加位置距约束端距离的增加,薄壁板的最大变形和最大应力呈增加趋势。随着SiC颗粒体积分数从5%增加到40%,薄壁板的变形和应力均变化不大,当体积分数从40%增加到56%时,应力明显减小,载荷作用位置距离约束端越远,最大变形减小的趋势越大。     

无压浸渗法制备不同体积分数及梯度SiCp/Al复合材料

选用不同粒径大小的SiC颗粒,并通过对颗粒分布的有效控制,采用无压浸渗工艺制备了不同体积分数(15%～65%)的SiCp/Al复合材料,并在此基础上试制了梯度SiCp/Al复合材料.运用OM,XRD等手段对所制备的复合材料进行了显微组织观察与成分分析,并对选定体积分数的复合材料进行了密度以及力学测试.研究结果表明,无压浸渗工艺下不同体积分数的SiCp/Al复合材料组织均匀、致密,力学性能良好;具有梯度结构的SiCp/Al复合材料层间结合良好,没有层间剥离现象.     

电子封装用SiCp/Al复合材料的组织与性能

本文选用粒径为20μm和60μm的SiC混合颗粒,采用挤压铸造方法制备了体积分数为70%的SiCp/LD11(Al-12%Si)复合材料.材料组织致密,颗粒分布均匀.复合材料具有低膨胀、高导热的特性和十分优异的力学性能,并且可以通过退火处理进一步降低其热膨胀系数.采用化学镀方法,在复合材料表面涂覆镍层,以其做为底座的二极管满足器件的可靠性测试要求.     

Er对原位ZrB2/A356.2复合材料组织与性能的影响

采用原位合成法制备ZrB_2/A356.2复合材料,研究了引入ZrB_2对A356.2铸态微观组织的影响以及不同Er含量对复合材料铸态微观组织及力学性能的影响。结果表明,引入ZrB_2后α-Al晶粒和粗大共晶Si发生略微细化,添加Er后α-Al晶粒细化明显,并且Er对共晶Si有很好的变质效果,α-Al由粗大树枝晶变为蔷薇状、球状,共晶Si从粗大的针片状变为细小的短棒状、球状,有效提高了复合材料的力学性能。当Er添加量为0.10%(质量分数)时,其细化变质效果最为明显,复合材料力学性能提高最为显著。     

Fabrication of an electronic package box of SiCP/Al composites with high volume SiCP

In this paper, a SiC_P preform was prepared by Powder Injection Molding (PIM), and the melting aluminum was injected into the SiC_P preform by the pressure infiltration method to manufacture an electronic package box of SiC_P (65%)/Al composites. SiC_P (65%)/Al composite prepared by pressure infiltration has full density and a homogeneous microstructure. The relative density of the composite is higher than 99%, the thermal expansion coefficient and thermal conductivity of the composite are 8.0×10⁻⁶/K and nearly 130 W/(m · K) at room temperature, respectively, which meet the requirements of electronic packaging. Translated from Journal of Acta Materiae Compositae Sinica, 2006, 23(6): 109–113 (in Chinese)     

Promotion mechanism of electric current on SiCp/Al composite material deformation

To solve the problem of poor formability of SiC_p/Al composite material, enhance the efficiency and reduce the consumption, current is adopted in hot forming process. Under the action of current, the plastic forming performance has made a huge improvement. It is verified that the detour flow and concentration of electrons may lead to a local liquid layer. In addition, the current flows through the crack tip can relax the stress concentration and prevent the propagation of crack. Otherwise, drifting electrons would collide with dislocation which generates electron wind force to make the dislocations arrange along the current direction. Therefore the electric current can enhance the formability of SiC_p/Al composite material and improve the quality of forming part.     

Mechanical properties of Cu/SiCp composites fabricated by composite electroforming

The silicon carbide particles (SiC_p) dispersion-strengthened copper matrix composites (Cu/SiC_p) were fabricated by composite electroforming technology. The microstructure, tensile property and wear behavior of Cu/SiC_p composites were investigated. The results showed that composites with different SiC_p contents were obtained. The microstructure of the composite presented a uniform distribution of SiC_p in the matrix and good interfacial integrity. The hardness, yield strength and rigidity of the composites increased with increasing SiC_p content, but at the cost of ductility. Increasing SiC_p content in the composite was not always beneficial to the ultimate tensile strength and wear resistance. The ultimate tensile strength increased with SiC_p content increasing up to 16 vol.% and decreased as exceeding 16 vol.%, and the wear mass loss decreased with SiC_p content increasing up to 21 vol.% and increased again as exceeding 21 vol.%.     

Effects of particle size and properties on the microstructures,mechanical properties,and fracture mechanisms of 7075Al hybrid composites prepared by squeeze casting

To investigate the effects of particle size and properties on the mechanical properties of 7075Al matrix composites, hybrid composites reinforced using three different reinforcement combinations, 40 vol. % 7 μm SiC_p with 5 vol. % 7 μm SiC_p, 35 μm SiC_p, and 35 μm Ti, were prepared using squeeze casting. The failure mechanisms and the microstructure–property relationships of hybrid composites were studied using SEM, TEM, and tensile tests. The composite containing Ti particles achieved the highest tensile strength of 626 MPa and an elongation of 1.2 %. Fracture mechanism analyses imply that the reduced strength for the 35 μm SiC_p-containing composite are caused by the inefficient load transfer capability resulting from the preferential breakage of larger-sized SiC_p particles during the deformation process. In contrast, micro-zones formed by Ti particles at the center and matrix alloy with few dislocations around release stress and deform synergistically during deformation, which decreases the breakage of SiC_p and improves the plastic deformation ability of the matrix alloy, resulting in a good combination of strength and ductility.     

Analyses on fracture characteristics of SiCp-6061Al/6061Al composites extruded by different ratios

Two 6061 Al alloy matrix composites reinforced with rods that are themselves composites of the same Al alloy reinforced with a high volume fraction of SiC particles were studied. After vacuum pressure infiltration, one was hot extruded at a ratio of 10 : 1 and the other at a ratio of 60 : 1. The fracture characteristics of the two SiC_p-6061Al/6061Al composites were examined in detail. It was found that increasing the hot extrusion ratio of this kind of composite can improve the bonding between the SiC_p-6061Al bars and the 6061Al matrix. The strengths of the SiC_p-6061Al bars and the 6061Al matrix were considered to increase with increasing extrusion ratio. Thus, the SiC_p-6061Al/6061Al composite extruded at a ratio of 60 : 1 shows fracture characteristics which are different from the composite extruded at a ratio of 10 : 1. The former has a higher fracture toughness, and its crack opening displacement versus load curve indicates a higher elastic modulus and maximum load. After application of the maximum external load, there is a slow decrease with increasing crack opening displacement in the case of the 60 : 1 extruded composite, but the load can be maintained for wide crack opening displacement in the case of the 10 : 1 extruded composite.     

Studies on the fracture and flexural strength of Al/Sip composite

Pure aluminum matrix composite reinforced with a high volume fraction of silicon particles (Al/Si_p) was fabricated by gas-pressured infiltration. The results of four point flexural strength tests show that Al/Si_p has low flexural strength. The analysis of the fractograph reveals the fracture mechanism of Al/Si_p. The fracture of Al/Si_p is primarily dominated by the fracture of brittle silicon particles and the subsequent link up of damage through the matrix. The pre-existent microcracks in silicon particles that were made during the process of compacting will also lower the flexural strength of Al/Si_p composite. The hybrid particle reinforced pure aluminum matrix composite (Al/Si_p+SiC_p) was fabricated in the same way. Results show the flexural strength can be improved by 11.3% compared with Al/Si_p when 6 vol.% silicon particles are replaced by silicon carbide particles with the same volume fraction and size. The reason is that SiC_p with higher fracture stress and higher elastic modulus can prevent the rapid expansion of cracks through the composite and lower the stress in silicon particles.     

Incorporation of new technique for processing of Al/SiCp composites based on evaporative pattern casting (EPC) method

Abstract

A336 Al matrix composites containing different volume fraction and mean mass particle size of SiC particles as the reinforcing phase were synthesised by evaporative pattern casting (EPC) route. The process consisted of fabricating of EPS/SiC_p composite pattern followed by EPC of A336 Al alloy. The EPS/SiC_p pattern was made by blending SiC particles with expandable polystyrene (EPS) beads and placing them in expanding mould heating with steam until EPS beads expand completely. Uniform distributed SiC particles around the EPS beads and locally movement of them during pouring and degradation leads to homogenous distribution of particles in final Al/SiC_p composite. Higher modulus, strength and hardness were observed in the composites than the unreinforced Al alloy part. The fracture surfaces of the composite samples exhibited dimple surfaces and fracture in SiC particles.     

Refining SiCp in reinforced Al–SiC composites using equal-channel angular pressing

Aluminum–silicon carbide composite (Al–SiC_p) is one of the most promising metal matrix composites for their enhanced mechanical properties and wear resistance. In the present study, Al–SiC (average size 55 μm) composites with 5% and 10% by volume were fabricated by stir casting technique. The equal-channel angular pressing (ECAP) was then applied on the cast composites at room temperature in order to study the effect of ECAP passes on the SiC_p size and distribution. The ECAP process was successfully carried out up to 12(8) passes for Al–5%(10%)SiC samples. Microstructure study revealed that the highest refinement by breakage of SiC_p was achieved after the first ECAP pass and that further refinement took place in the next passes. More breakage of the SiC_p was found in the composite richer in reinforcing particles so that the SiC_p reached approximately 1 μm in the Al–10%SiC after 8 passes and 4 μm in Al–5%SiC after 12 ECAP passes. The distribution of SiC reinforcement particles also improved after applying ECAP. The factors including decrease in reinforcing particle size, improvement in their distribution, decrease in porosity in addition to strain hardening and grain refining of the matrix resulted in enhancement of tensile and compressive strengths as well as hardness by more than threefold for the Al–5%SiC after 12 passes and for Al–10%SiC after 8 passes compared to the cast composites. Additionally, the composite remained ductile after the ECAP process. The fracture surface indicated good bond between the matrix and the reinforcement.     

Development of Al356/SiCp cast composites by injection of SiCp containing composite powders

One of the great challenges of producing cast metal matrix composites is the agglomeration tendency of the reinforcements. This would normally result in poor distribution of the particles, high porosity content, and low mechanical properties. In the present work, a new method for uniform distribution of very fine SiC particles with average size of less than 3 μm was employed. The key idea was to allow for gradual in situ release of properly wetted SiC particles in the liquid metal. For this purpose, SiC particles were injected into the melt in three different forms, i.e., untreated SiC_p, milled particulate Al–SiC_p composite powder, and milled particulate Al–SiC_p–Mg composite powder. The resultant composite slurries were then cast from either fully liquid (stir casting) or semisolid (compocasting) state. Consequently, the effects of the casting method and the type of the injected powder on the microstructural characteristics as well as the mechanical properties of the cast composites were investigated. The results showed that the distribution of SiC particles in the matrix and the porosity content of the composites were greatly improved by injecting milled composite powders instead of untreated-SiC particles into the melt. Casting from semisolid state instead of fully liquid state had similar effects. The average size of SiC particles incorporated into the matrix was also significantly reduced from about 8 to 3 μm by injecting milled composite powders. The ultimate tensile strength, yield strength and elongation of Al356/5 vol.%SiC_p composite manufactured by compocasting of the (Al–SiC_p–Mg)_cp injected melt were increased by 90%, 103% and 135%, respectively, compared to those of the composite manufactured by stir casting of the untreated-SiC_p injected melt.     

Damping behavior of Al/SiCP multilayer composite manufactured by roll bonding

High damping materials comprising good mechanical properties as structural materials and high damping capacity for vibration loading are the best solutions for vibration problem. In current study, functionally graded material from composite sheets with different percentages of reinforcement was manufactured by hot rolling process. The damping behavior of base alloy composite including different percentages of SiC particles and Al/SiC_P multilayer composite sheets was studied at room temperature conditions. The Al/SiC_P composites were found to exhibit higher damping capacity compared to Al alloy. The damping capacity increased by increase in the percentage of reinforcement. Furthermore, Al/SiC_P multilayer composite sheet provided higher damping capacity in comparison to Al alloy. Therefore, damping capacity enhanced by increasing the number of layers. The main source for damping behavior in composite materials is dislocation damping whereas in stepwise multilayer composite sheets, it comes from boundary conditions between layers.