Al_2O_3/Al合金复合材料的蠕变与回蠕变行为

CREEP AND BACK CREEP BEHAVIOURS OF Al_2O_3/Al BASED ALLOY COMPOSITES

研究了挤压铸造 Ａｌ_２Ｏ_３短纤维（体积分数为 １５％）增强 Ａｌ合金 Ａｌ－Ｓｉ１２－Ｃｕ１－Ｍｇ１－Ｎｉ１复合材料的变载荷蠕变和回蠕变行为．结果表明，复合材料在主应力作用下蠕变当载荷突然降低后，表现为瞬态大应变量收缩以及随后的回蠕变．研究表明初始瞬态收缩完全是复合材料的弹性应变，有别于前人采用复合材料或纯金属、合金所得到的数倍于弹性应变结果．实验结果经数值回归得出回蠕变速率，回蠕变应变 ＝Ａ ｌｎ ｔ＋Ｃ．指数ｎ在任一主应力应变阶段均接近于－１，系数Ａ取决于降载前复合材料积累的主应力蠕变状态，并随降载前主应力蠕变程度的增加而增大，表明复合材料回蠕变行为受到降载前主应力蠕变状态的制约．

Creep experiments with sudden load changes were performed on Al-Si12-Cu1- Mg1-Ni1 alloy reinforced with 15% (volume fraction) of alumina short fibers (Saffil). Upon unloading, an immediate strain response is observed followed by a continuous back creep process. It was found that the transient strain response is just an elastic contraction of the composite, which is different to the results obtained with composite, alloy as well as pure metal and alloys in the literatures. During the back creep process the creep rate law can be described as bc(t) = Atn, and the creep strain law bc(t) = A In t + C, which were regressed from the experimental results. The exponent n in the creep rate law is close to --1 at any stage in the creep life. The coefficient A in both formulas depends on the creep strain accumulated prior to unloading. This implies that the preceding creep history of major stress has influence on the back creep behavior.