冷热循环对颗粒增强铝基复合材料微屈服行为的影响

采用微屈服强度测试、透射电镜和高分辨透射电镜分析,对经过不同冷热循环工艺处理后的颗粒增强铝基复合材料的微屈服行为进行了研究。结果表明,冷热循环次数虽然对颗粒增强铝基复合材料微屈服行为的宏观规律没有本质的影响,但是仍然影响颗粒增强铝基复合材料的微屈服行为。对球形颗粒而言,小应变量下的微屈服强度随冷热循环次数的增加而增高;但对棱形颗粒而言,循环次数的影响较为复杂。研究还表明,冷热循环次数影响颗粒增强铝基复合材料微屈服行为的主要原因是其位错组态和残余应力在不同的循环次数下有明显的不同。     

搅拌参数对半固态搅拌工艺制备(ABO_w+SiC_p)/6061Al复合材料微观组织和力学性能的影响(英文)

采用不同半固态机械搅拌工艺(变化搅拌温度和搅拌时间),制备硼酸铝晶须(ABOw)和碳化硅颗粒(SiCp)混杂增强6061铝基复合材料。利用扫描电镜(SEM)、X射线衍射(XRD)、透射电镜(TEM)和拉伸试验研究搅拌工艺参数对复合材料微观组织和力学性能的影响。结果表明:在可以搅拌的情况,增强体在复合材料中分布的均匀性和复合材料的力学性能随着搅拌温度的降低和搅拌时间的延长而得到提高。基于对复合材料微观组织的观察和力学性能的测试得到最佳的搅拌工艺参数为:搅拌温度640℃,搅拌时间30min。     

A comparative study on microstructural evolution and surface properties of graphene/CNT reinforced Al6061−SiC hybrid surface composite fabricated via friction stir processing

A comparative study on the surface properties of Al−SiC−multi walled carbon nanotubes (CNT) and Al−SiC−graphene nanoplatelets (GNP) hybrid composites fabricated via friction stir processing (FSP) was documented. Microstructural characterization reveals a more homogeneous dispersion of GNPs in the Al matrix as compared to CNTs. Dislocation blockade by SiC and GNP particles along with the defect-free interface between the matrix and reinforcements is also observed. Nanoindentation study reveals a remarkable ∼207% and ∼27% increment in surface nano-hardness of Al−SiC−GNP and Al−SiC−CNT hybrid composite compared to as-received Al6061 alloy, respectively. On the other hand, the microhardness values of Al−SiC−GNP and Al−SiC−CNT are increased by ∼36% and ∼17% relative to as-received Al6061 alloy, respectively. Tribological assessment reveals ∼56% decrease in the specific wear rate of Al−SiC−GNP hybrid composite, whereas it is increased by ∼122% in Al−SiC−CNT composite. The higher strength of Al−SiC−GNP composite is attributed to the mechanical exfoliation of GNPs to few layered graphene (FLG) in the presence of SiC. Also, various mechanisms such as thermal mismatch, grain refinement, and Orowan looping contribute significantly towards the strengthening of composites. Moreover, the formation of tribolayer by the squeezed-out GNP on the surface is responsible for the improved tribological performance of the composites. Raman spectroscopy and various other characterization methods corroborate the results.     

Superplastic behavior of PM SiCp/6061 aluminum alloy composites at high strain rates

The superplastic behavior of a powder-metallurgy processed 6061 Al composite was investigated as a function of SiC content increasing from 0% to 30% at 10% increments over a wide temperature range from 430°C to 610°C. The materials were found to be high-strain-rate superplastic. In the temperature range where grain boundary sliding (GBS) controlled the plastic flow, the strength of the composite was lower than that of the unreinforced matrix alloy even after compensating for grain size and threshold stress. This “particle weakening” was in contrast with the particle strengthening observed in the low temperature range where dislocation climb creep was found to control the plastic flow. In the GBS regime, the strength differential between the materials was a function of SiC content and temperature, which increased with the increase in SiC content and temperature. Strong Mg segregation was detected at interfaces between SiC and Al phases in the composites. Evidence for interfacial reaction reported in the Si₃N₄ reinforced 6061 Al composites could not be detected in the current composites. Extensive formation of whisker-like fibers was observed at the fractured surface of the tensile samples above the critical temperature where particle weakening begins to be exhibited. This result suggests the possibility that partial melting in the solute-enriched region near SiC interfaces is responsible for the particle weakening in the SiC reinforced 6061 Al composite.     

一种由MCNP设计,通过SPS加热轧制备的新型辐射屏蔽复合材料

本研究旨在设计和制备一种新型的中子和γ射线辐射屏蔽复合材料。基于蒙特卡罗模拟,含不同W质量分数(40~70%)的新型(W+B)/6061Al复合材料首次采用球磨法和SPS加热轧制法制备,并对其组织和力学性能进行了研究。实验结果显示,轧制之后,W和B颗粒均匀分布于基体中,而且W/Al界面以固溶体的形式呈现出良好的冶金结合。复合材料的物相主要包括W和Al。EBSD结果表明,W颗粒具有促进动态再结晶(DRX)成核、限制晶粒长大和降低6061Al基体织构的作用。拉伸试验表明,W含量为50 wt.%的复合材料强度最高,塑性较好。结合模拟结果,该组分的复合材料性能达到了实际应用要求。(W+B)/6061Al复合材料的强化机理包括位错强化和载荷传递效应。     

亚微米Al2O3颗粒表面稀土改性及其对6061Al复合材料时效行为的影响

采用液相包裹法对亚微米Al2O3颗粒进行稀土表面改性，用挤压铸造法制备表面经稀土改性的Al2O3p／6061Al复合材料．对颗粒表面经稀土改性前后增强6061Al复合材料在不同温度下的时效析出行为进行分析研究．结果表明：改性后的亚微米Al2O3粉体颗粒表面Y2O3包裹均匀，其增强的复合材料在不同时效阶段的硬度值均较改性前有明显提高．且随着时效温度的升高，Mg2Si析出过程加快，时效峰提前，呈现出硬度值变小的趋势，透射电镜观察表明，表面改性颗粒增强的复合材料基体中存在一定量的位错和析出相；而改性前复合材料却呈现出位错和析出相极其稀少的组织特征．分析了改性前后复合材料时效组织形成的原因。     

Effect of fabrication method on the aging behavior of 6061 Al matrix composites reinforced with SiC whiskers

Age hardening behaviors of SiC whisker reinforced composites with 6061 Al matrix fabricated by P.M. (powder metallurgy) and squeeze casting were investigated to examine the effect of the fabrication method on the aging kinetics. In the squeeze cast composite, numorous triangular particles which is believed to be MgAlp₂O₄ were observed at Al/SiC interfaces whereas no visible interface particles were observed in the P. M. composite. P.M. composite showed faster age hardening and reached the maximum hardness earler than the squeeze cast composites. The decrease of the aging kinetics in squeeze cast 6061 Al matrix composites compared to that in P.M. composites is thought to result from more severe depletion of Mg atoms due to interfacial reactions in squeeze cast composites. The uniformity of whisker distribution is suggested to influence the general aging behavior through its effect on the local dislocation density. Data on the aging kinetics and the interfacial reactions in other Al alloys were also examined to study various factors which can influence the aging kinetics.     

FATIGUE BEHAVIOUR OF SiC_p/6061Al COMPOSITE

The fatigue of SiC_p/6061Al composite containing 15 v.-% SiC particles has been compared with 6061Al alloy.Dislocation structure and microprocess of fatigue crack initiation and propagation in the composite have been investigated by using SEM and TEM.The results in- dicate that the fatigue strength at 10~7 cycles of the composite is 196 MPa,i.e.about 25% higher than matrix alloy.The voids and microcracks initiated at and near the interface be- tween SiC_p and matrix,where has a higher density of dislocations,will propagate and link up to form the fatigue crack.It is an important evidence to note that the dislocation channels where screw dislocation can travel are formed near interface and corner region of SiC_o in the composite subjected to fatigue stress(σ_(max)=274 MPa N=2.4×10~5 cycles),demonstrating the relationship between fatigue crack initiation and dislocation movement in the SiC particles reinforced 6061 Al alloy composite.     

Effect of SiC volume fraction on the age-hardening behavior in SiC particulate-reinforced 6061 aluminum alloy composites

The age-hardening behavior in the SiC particulate-reinforced 6061 aluminum alloy composites (SiCp/6061 Al alloy composites) was investigated using hardness measurement, calorimetric technique and transmission electron microscopy. The aging time for the peak hardness in 10%SiCp/6061 Al and 20%SiCp/6061 Al alloy composites was shorter than that of the unreinforced 6061 Al alloy, and the age-hardening was most accelerated in the 20%SiCp/6061 Al alloy composite. It is induced from the high density of dislocations in SiCp/6061 Al alloy composites which act as heterogeneous nucleation sites of precipitates and as a high diffusivity path of alloy elements. The precipitation sequence and the aspect of precipitates in the 6061 Al alloy cannot be affected considerably by the presence of SiC particulate and the volume fraction of SiC particulate. The activation energies for the formation of the intermediate β' phase in the unreinforced 6061 Al alloy, 10%SiCp/6061 Al and 20%SiCp/6061 Al alloy composite were 142.6 kJ/mol, 127.3 kJ/mol, 106.1 kJ/mol, respectively.     

Deformation behavior of SiC particle reinforced Al matrix composites based on EMA model

Effects of the matrix properties,particle size distribution and interfacial matrix failure on the elastoplastic deformationbehavior in Al matrix composites reinforced by SiC particles with an average size of 5μm and volume fraction of 12%werequantitatively calculated by using the expanded effective assumption(EMA)model.The particle size distribution naturally bringsabout the variation of matrix properties and the interfacial matrix failure due to the presence of SiC particles.The theoretical resultscoincide well with those of the experiment.The current research indicates that the load transfer between matrix and reinforcements,grain refinement in matrix,and enhanced dislocation density originated from the thermal mismatch between SiC particles and Almatrix increase the flow stress of the composites,but the interfacial matrix failure is opposite.It also proves that the load transfer,grain refinement and dislocation strengthening are the main strengthening mechanisms,and the interfacial matrix failure and ductilefracture of matrix are the dominating fracture modes in the composites.The mechanical properties of the composites strongly dependon the metal matrix.     

Preparation, microstructures and deformation behavior of SiCP/6066Al composites produced by PM route

Preparation, microstructures and deformation behavior of 12 vol.% SiC_P/6066Al composites fabricated by a powder metallurgy (PM) route have been systemically reported in this paper. The experimental results indicated that SiC particles were distributed homogeneously in the aluminum matrix, and that the constituents of the matrix were Al, needle-shaped β′-Mg₂Si phases and a small amount of dispersoids (Fe, Mn, Cu)₃Si₂Al₁₅ (BCC structure with lattice parameter a ≈ 12.8 Å). A well-bonded SiC/Al interface consisting of a thin and clean layer of polycrystalline structure of metal matrix with segregation of Mg element has been observed. The SiC particle cracking and the ductile-tearing of SiC/Al interfaces caused the rupture of the composites. The experimental data coincided well with the theoretical results predicted by an extended effective model assumption (EMA). The current study indicates that load transfer between the matrix and reinforcements, grain refinement of metal matrix, and dislocation strengthening are the main strengthening mechanisms of SiC_P/Al composites. The ductile-tearing of SiC_P/Al interfaces and the SiC particle cracking are the dominating failure modes and the deformation behavior of SiC_P/Al composites strongly depends on the properties of matrix alloy.     

铸造ZL101A／SiCp复合材料的研究

采用真空搅拌复合工艺制备了铸造ZL101A／SiC复合材料,研究了变质和细化处理对复合材料组织的影响。结果表明：变质和细化处理铸造 ZL101A／SiC复合材料制备工艺的重要处理措施,可明显改善复合材料的组织。利用透射电镜对AL／SiC界面特征及界面反应进行分析,同时对该复合材料的铸造性能（熔体合金流动性能、线收缩、体收缩和热裂倾向）以及力学和物理性能进行了测试。     

铸造SiCp／2024复合材料微观结构与强化机制的研究

研究了SiC体积分数分别为5,10,15和20%的2024Al基复合材料在峰值时效态下的微观结构和强化机制透射电镜观察和Vickers硬度测定表明:增强相的加入使复合材料基体中的位错密度升高,亚晶尺寸略有下降,但基体的硬度却无明显升高拉伸试验发现,弹性模量和加工硬化指数随SiC体积分数增加而显著提高,初始流变应力先下降后升高本文认为由增强相导致的应力集中和基体形变的高约束度是控制SiC_p/2024复合材料形变与强化的两个主要因素     

Welding of SiC particle reinforced 6061 Al matrix composite with pulsed TIG

1　INTRODUCTIONDiscontinuously(particle,whiskerandshortfiber)reinforcedaluminumalloycompositeshavebecomeanattractivestructuralmaterialformanyindustrialfieldsowingtoitsexcellentproperties(e.g.highspecificstrength,highspecificstiffnessandgoodwearresistance)…     

Origin of Insignificant Strengthening Effect of CNTs in T6-Treated CNT/6061Al Composites

Carbon nanotube(CNT)-reinforced 6061 Al(CNT/6061 Al) composites were fabricated via powder metallurgy combined with friction stir processing(FSP). CNTs were dispersed after FSP and accelerated the precipitation process of the CNT/6061 Al composites. However, the strengthening effect of CNTs on the T6-treated materials was insignificant,while the composites under the FSP and solution treatment conditions exhibited increased strength compared to the matrix.Precipitate-free zones(PFZs) were detected around CNTs in the T6-treated CNT/6061 Al composites, and a model was proposed to describe the effect of PFZs on strength. The calculations indicated that the strength of PFZs was similar to that of the T6-treated 6061 Al. As a result, the strengthening effect of CNTs on the T6-treated CNT/6061 Al composites was insignificant.     

有限元模拟SiC增强Al基复合材料的力学行为

采用有限元方法和轴对称单胞模型模拟了增强体(SiC)形状、体积分数以及不同基体类型对铝基复合材料力学行为的影响。模拟结果表明:增强体的加入会阻碍基体的塑性流变,使基体内发生非均匀变形,在增强体尖角处出现应力集中;椭圆柱形增强体对基体塑性变形的阻力最大,传递载荷的能力最强,因此强化效果最好。在一定范围内,随着增强体体积分数的增加,基体与增强体之间的比表面积增大,有利于载荷的传递;增强体体积分数的增加导致颗粒间距减小,几何必须位错自由运动的路径减少,复合材料的强度也随之增加。此外,不同类型基体自身的塑性流变能力不同,Al-Zn-Mg基体强度最高,在拉伸变形过程中,受到增强体的阻碍作用最大,会有更多的载荷从基体传递到增强体,以Al-Zn-Mg为基体的复合材料的强度最高。     

Microstructure and damping behavior of SiCp/Gr/2024Al metal matrix composites by squeeze casting technology

SiCp/Gr/2024Al metal matrix composites were processed by squeeze casting technology. The microstructure of composites was observed by SEM and TEM, and the effects of graphite particulates and SiC particulates on the damping behaviors of composites were also investigated. The results show that the microstructure of composites was dense and homogeneous, without any interfacial reactivity among reinforcement/matrix interfaces. Compared with the damping capacity of 2024Al, the damping capacity of composites was enhanced significantly by addition of SiC or graphite particulates. The main damping mechanisms of SiCo/Al composites were ascribed to the dislocation damping, and those of SiCo/Gr/2024Al were attributed to the intrinsic damping and interface damping.     

SiC_p/Al复合材料的制造及新动向

颗粒增强铝基复合材料是当前研究较多、比较成熟、应用较广泛的金属基复合材料,SiCp/Al是其中的一类。本文综述了SiCp/Al复合材料的发展状况、制备方法、存在的技术难题,提出了今后需要完善和进一步研究的方向。     

低温循环过程中SiCw／6061Al复合材料残余应力的变化规律

研究了低温循环过程中压铸态ＳｉＣｗ／６０６１Ａｌ复合材料残余应力的变化零乱低温循环的降温阶段,复合材料基体经历错配拉伸塑性变形过程在升温阶段基体国卸载过程。经过一次低温循环后,残余应力有所降低。如果进行两次低循环自理只有当第二次循环下降温度低于第一次时,才能再次降低复合材料残余应力。     

Fabrication of Al6061 composite with high SiC particle loading by semi-solid powder processing

Aluminum alloys reinforced with silicon carbide (SiC) particles have been studied extensively for their favorable properties in structural and thermal applications. However, there has been only limited research into investigating the loading limit of a reinforcement phase of a metal matrix composite. In this paper, semi-solid powder processing (SPP), a fabrication method that exploits the unique behavior of a solid–liquid mixture, was used to synthesize SiC particle-reinforced Al6061. A high volume loading (>45 vol.%) of SiC in Al6061 matrix was investigated by varying the SiC loading volume fraction, forming pressure, SiC particle size and Al6061 particle size. The compaction and synthesis mechanism of the composite by SPP was discussed based on reinforcement phase compaction behavior and processing parameters. Microstructure, hardness, fracture surface and X-ray diffraction results were also analyzed. Results showed that SPP can achieve over 50 vol.% loading of SiC in Al6061 matrix with near theoretical density.