SiC颗粒增强6061Al基复合材料的动态拉伸性能Ⅱ应变速率效应

用拉伸split Hopkinson bar实验装置进行了SiCp/6061Al得合材料及基体合金的动态拉伸实验，研究了材料的应变速率敏感性。结果表明，SiCp/6061Al复合材料及其基体合金均具有明显的应变速率效应，且复合材料的应变速率敏感性高于基体合金的应变速率敏感性，根据位错机制对此进行了解释。     

热挤压对SiCw·SiCp/2024Al组织与性能的影响

为了研究SiCw·SiCp/2024Al复合材料的热变形行为,对压铸法制备的SiCw·SiCp/2024Al复合材料进行了热挤压变形,并测定了其变形前后的室温拉伸性能.利用扫描电镜和透射电镜对复合材料热变形前后的微观组织进行观察.研究表明:增强体在基体中分布均匀,并与基体有良好的界面结合;热挤压后,纳米颗粒分布的均匀性和分散性得到改善,SiC晶须产生了沿挤压方向的定向排列,且SiC晶须与基体合金的界面结合良好;随着SiC颗粒含量的增加,混杂增强复合材料的抗拉强度随之升高,挤压后复合材料的抗拉强度进一步提高;与基体合金相比,混杂增强复合材料的延伸率下降,热挤压有利于提高混杂复合材料的延伸率.     

W丝/Zr基非晶合金复合材料动态拉伸断裂模式研究

采用霍普金森杆拉伸技术研究了W丝体积分数为80%的W丝/Zr基非晶合金复合材料的动态拉伸性能,通过扫描电镜研究了该复合材料动态拉伸断裂模式.结果表明:随着打击速度增加,复合材料动态拉伸强度和断裂应变总体呈上升趋势;复合材料的动态拉伸断裂模式以钨丝解理断裂为主导,伴随非晶合金基体产生脉纹状花样和钨丝劈裂;脉纹状花样的形态不同于在动态压缩条件下所形成的,不存在"尖脊"形貌.     

SiCp/Al-Li复合材料的微观结构性能、及断裂特征

本文对粉末冶金法制备的SiCp/Al-Li复合材料进行了不同温度的拉伸试验和透射电镜分析,结果表明,该复合材料具有高的室温强度和低的延伸率。在复合材料基体晶界和SiC颗粒界面处均存在一定宽度的无沉淀带。微裂纹常在基体晶界和SiC颗粒界面处形成。复合材料的断裂形貌为韧窝加沿晶断裂。      

SiGw/Al复合材料的偏轴拉伸断裂行为

应用扫描电镜对挤压SiCw/6061Al复合材料的拉伸断裂过程进行了动态观察,并详细讨论了偏轴角θ对复合材料强度和断裂行为的影响。结果表明,微裂纹起源于晶须周围基体中,其萌生与扩展受晶须偏轴角的控制。复合材料由正向断裂向剪切断裂转变的特征角θ₀约为45-50°。      

数值模拟SiCp/Al复合材料的微观结构对力学性能的影响

本文运用有限元法模拟了SiC颗粒体积分数和颗粒尺寸对SiCp/Al复合材料弹性模量、屈服强度、延伸率的影响。为了建立与真实显微结构相似的复合材料模型,假定任意尺寸的SiC颗粒随机地分布在SiCp/Al复合材料中。计算结果表明:SiC颗粒体积分数对复合材料的力学性能的影响更加显著。随着体积分数的增加,SiCp/Al复合材料的弹性模量和屈服强度逐渐增加;而其延伸率会相应降低。其应力应变曲线由韧性材料的特性向脆性材料的特性逐渐过渡。相反,当平均颗粒尺寸在一定的范围内变化时,颗粒尺寸对其应力-应变曲线的影响并不显著。     

双屏蔽(B4C-W)/6061Al层状复合板设计与性能

基于B₄C和W良好的屏蔽中子和γ射线性能,采用6061铝合金作为基体,设计了一种新型双屏蔽(B₄C-W)/6061Al层状复合材料,通过放电等离子烧结后加热轧制成板材,对制备的复合材料微观组织和力学性能进行了研究。结果表明,屏蔽组元B₄C和W颗粒均匀地分布在6061Al基体中,层界面、B₄C/Al、W/Al异质界面之间结合良好,无空隙和裂纹。在颗粒与基体界面处形成扩散层,扩散层的厚度约为6 μm (W/Al)和4 μm (W/Al)。轧制态的(B₄C-W)/6061Al层状复合板的屈服强度(109 MPa)和极限抗拉强度(245 MPa)明显优于烧结态的复合材料,但断裂韧性降低。强度提高的原因主要是轧制后颗粒的二次分布、均匀性及界面结合强度提高,基体合金的晶粒尺寸减小,位错密度增加。层状复合板的断裂方式为基体合金的韧性断裂和颗粒的脆性断裂。      

SiC晶须对SiCw/6061Al复合材料拉伸和压缩变形行为的影响

通过试验研究了SiCw/6061Al复合材料和6061Al基体的拉伸和压缩变形行为.结果表明,SiCw/6061Al复合材料和6061Al的拉伸变形行为相同,而压缩变形曲线上出现应力峰,这与不同应力状态下SiC晶须的转动有关.拉伸时SiC晶须逐渐转向与外力平行方向使SiCw/6061Al复合材料的应力增大,而压缩时SiC晶须转向与外力垂直方向使其应力减小,而不是由动态再结晶引起.     

SiGw/Al复合材料的偏轴拉伸断裂行为

应用扫描电镜对挤压SiCw/6061Al复合材料的拉伸断裂过程进行了动态观察,并详细讨论了偏轴角θ对复合材料强度和断裂行为的影响。结果表明,微裂纹起源于晶须周围基体中,其萌生与扩展受晶须偏轴角的控制。复合材料由正向断裂向剪切断裂转变的特征角θ₀约为45-50°。     

SiC_p/2024Al复合材料尺寸稳定化处理工艺研究

采用挤压铸造技术制备了体积分数为40%的SiCp/2024Al复合材料,采用TEM对不同尺寸稳定化处理条件下复合材料的微观组织进行了观察,并探讨了尺寸稳定化热处理工艺对复合材料拉伸性能的影响.TEM观察表明:由于SiC颗粒与2024Al基体的热膨胀系数不同,热错配的作用使冷热循环处理后基体中的位错密度增加,为S′相的形成提供了有利的形核部位,促进了S′相的析出,这两种因素都有利于提高复合材料的强度.室温拉伸测试结果表明:零次冷热循环热处理后的SiCp/2024Al复合材料拉伸强度比较好,两次冷热循环处理后复合材料的强度有所下降,但随着循环次数的增加,复合材料的强度逐渐增加;不同的冷热循环次数对于拉伸断裂方式和断口形貌无显著影响.     

Failure of AA 6061 and 2099 aluminum alloys under dynamic shock loading

Microstructural aspects of the deformation and failure of AA 6061 and AA 2099 aluminum alloys under dynamic impact loading are investigated and compared with their responses to quasi-static mechanical loading in compression. Cylindrical specimens of the alloys, heat-treated to T4, T6 and T8 tempers, were subjected to dynamic compressive loading at strain rates of between 2800 and 9200 s⁻¹ and quasi-static compressive loading at a strain rate of 0.0032 s⁻¹. Plastic deformation under the dynamic impact loading is dominated by thermal softening leading to formation of adiabatic shear bands. Both deformed and transformed shear bands were observed in the two alloys. The shear bands offer preferential crack initiation site and crack propagation path in the alloys during impact loading leading to ductile shear fracture. While cracks propagate along the central region of transformed bands in AA 6061 alloy, the AA 2099 alloy failed by cracks that propagate preferentially along the boundary region between the transformed shear bands and the bulk material. Whereas the AA 2099 alloy shows the greatest propensity for adiabatic shear banding and failure in the T8 temper condition, AA 6061 alloy is most susceptible to formation of adiabatic shear bands and failure in the T4 temper. Deformation under quasi-static loading is dominated by strain hardening in the two alloys. Rate of strain hardening is higher for naturally aged AA 6061 than the artificially aged alloy, while the strain hardening rate for the AA 2099 alloy is independent of the temper condition. The AA 2099 alloy shows a superior mechanical behaviour under quasi-static compressive loading whereas the AA 6061 shows a higher resistance to impact damage.     

界面性能对SiCp/6061Al复合材料棘轮行为的影响

利用复合材料细观有限元分析方法,对SiC颗粒增强6061Al合金复合材料的单拉行为、单轴棘轮行为进行数值模拟。模拟中讨论了耦合自由边界、界面结合状态对复合材料棘轮行为的影响;同时,分析了基体和界面的微观变形特征及其演变规律。选取1组合理的微结构参数,对复合材料的棘轮行为进行数值模拟,并通过与实验结果的比较,检验有限元模型的合理性。结果表明：耦合边界很大程度改善了模拟结果;界面结合状态越好,即界面弹性模量、屈服强度和硬化模量越高,产生的棘轮变形越小;具有合理参数值的弱界面模型给出的棘轮变形预测结果比完好界面模型的结果更接近于实验值。     

SiCp/6151Al复合材料的微结构效应

利用分离Hopkinson压杆和MTS通用材料试验机研究了SiCp/6151A颗粒增强复合材料在不同应变率下的变形行为和增强颗粒的尺寸对复合材料微结构及变形行为的影响。结果:于在不同应变率下的SiCp/6151A复合材料，增强颗粒尺寸小的流动应力高于增强颗粒尺寸大的流动应力。根据位错强化理论中的Hall-Petch关系对这个结果进行了解释。首次在实验上观测到增强颗粒对复合材料微损伤－微带形成的影响，并根据微带（microband)形成的双位错墙理论（double dislocation walls)，分析了增强颗粒对复合材料微带损伤及力学性能影响的微结构效应。     

Deformation behaviour and microstructure of a 20% Al2O3 reinforced 6061 Al composite

Deformation and microstructural behaviours of a 20% (volume percent) particle reinforced 6061 Al matrix composite have been studied by torsion from 25 to 540°C with strain rates of 0.1, 1 and 5 s⁻¹. The logarithmic stress versus reciprocal temperature relationship exhibits two slopes indicating different deformation mechanisms. The 20% Al₂O₃/6061 Al composite shows a greater hardening behaviour than those of the 10% Al₂O₃/6061 Al composite and of the monolithic alloy. Above 250°C, TEM investigations reveal much smaller subgrain size and higher volume of non-cellular substructures, as well as dynamic recrystallization nuclei in the 20% Al₂O₃/6061 Al composite in comparison to those of the 10% Al₂O₃/6061 Al composite and matrix alloy the same test condition. The torsion fracture surface was studied and compared to the three point bending failure specimens.     

SiCw／6061A1复合材料温度循环拉伸变形行为

本文采用热循环拉伸试验方法研究了ＳｉＣｗ／６０６１Ａ１复合材料的变形行为．结果表明，ＳｉＣｗ／６０６１Ａ１复合材料温度循环拉伸变形行为与蠕变类似分为初始变形阶段、稳态变形阶段和快速断裂三个阶段；温度循环拉伸变形稳态流变速率明显提高；温度循环拉伸变形的应力指数低于恒温蠕变的应力指数．     

Effects of particulate reinforcement and strain‐rates on deformation and fracture behavior of Aluminum 6061‐T6 under high velocity impact

Aluminum matrix composites (AMC) exhibit an attractive combination of mechanical and physical properties such as high stiffness and low density, which favors their utilization in many structural applications. Thus, increasing the structural applications of AMC is the driving force for the need to adequately understand their deformation and failure mechanisms under various types of loading conditions. In this study, plastic deformation of alumina particle reinforced Aluminum 6061‐T6 matrix composite is investigated and compared to that of an un‐reinforced Aluminum 6061‐T6 alloy at high strain‐rates under compressive loading. Dynamic stress‐strain curves are obtained using direct impact Split Hopkinson Pressure Bar (SHPB). Particulate reinforcement increases the deformation resistance of the aluminum alloy at high strain‐rates. Strain localization along narrow adiabatic shear bands is observed in both the reinforced and un‐reinforced alloy. Whereas the microstructure of shear bands in un‐reinforced alloy showed finer grain size compared to that of the bulk material, the shear bands observed in the AMCs are darker than the bulk material and the reinforcing particles are observed to be more closely spaced along the shear bands.     

Hot deformation behaviour of aluminium alloy 6061/SiCp MMCs made by powder metallurgy route

Abstract

The hot deformation behaviour of a 20 vol.-%SiC particle reinforced Al alloy 6061 composite and Al alloy 6061, made via a powder metallurgy (PM) route and treated by a T4 temper, were studied by compression testing over a range of temperatures (300–500°C)and at strain rates of 0.005, 0.05, and 0.09 s^-1. It was observed that the flow stresses of the composites were significantly higher than those of the alloy at lower deformation temperatures. However, the stress–strain curves of both the composite and the alloy showed significant softening during deformation at the lowest strain rate, the softening for the composite being faster than that of the alloy. The activation energy for hot deformation was determined for different strains, using a power law equation, and was found to change significantly with strain for both the alloy and the composite. This phenomenon was explained by the occurrence of dynamic precipitation and coarsening during deformation.     

Low-cycle fatigue life of SiC-particulate-reinforced Al-Si cast alloy composites with tensile mean strain effects

The low-cycle fatigue behaviour of a SiC-particulate-reinforced Al-Si cast alloy with two different volume fractions has been investigated under strain-controlled conditions with and without tensile mean strains. The composites and the unreinforced matrix alloy showed cyclic hardening behaviour. The composite having a higher volume fraction of the SiC particles exhibited a more pronounced strain-hardening rate. For the tensile mean strain tests, the initial high tensile mean stress relaxed to zero for the ductile Al-Si alloy, resulting in no influence of the tensile mean strain on the fatigue life of the matrix alloy. However, tensile mean strain for the composite caused tensile mean stresses and reduced the fatigue life. The pronounced effects of mean strain on the low-cycle fatigue life of the composite compared to the unreinforced matrix alloy were attributed to the initial large prestrain causing non-relaxing high tensile mean stress in the composite with limited ductility and cyclic plasticity. Fatigue damage parameter using strain energy density accounted for the mean stress effects quite satisfactorily. Predicted fatigue life using this damage parameter correlated fairly well with the experimental life within a factor of 3. Moreover, the fatigue damage parameter indicated the inferior life in the low-cycle regime and superior life in the high-cycle regime for the composite, compared to the unreinforced matrix alloy.     

SiCp／Al复合材料的微观结构与界面

对用压力铸造法制造的碳化硅颗粒增强铝合金（ＳｉＣｐ／Ａｌ）复合材料的微观结构和界面进行了研究。结果表明：碳化硅颗粒在复合材料中均匀分布，复合材料的基体中有较高的位错密度，碳化硅颗粒中有少量的层错。研究还发现ＳｉＣｐ／Ａｌ复合材料中界面结合良好，没有反应物生成，并且在界面处没有发现孔隙存在。在复合材料拉伸断口上没有发现裸露的碳化硅颗粒，说明在复合材料拉伸破坏时ＳｉＣｐ－Ａｌ界面没有开裂，反映了压铸ＳｉＣｐ／Ａｌ复合材料中良好的界面结合。