摘要
在备有拉伸装置的扫描电镜下,观察了 Al—2.56 Li—1.29Cu 合金拉伸变形及断裂过程。观察结果表明,在固溶淬火及190℃时效状态下,主要析出相为δ’相。随着时效时间的延长,拉伸断口逐渐由韧窝穿晶型向沿晶突脊型及沿晶韧窝型过渡。在固溶状态下,当拉伸应力超过届服强度以后,出现平直滑移带及交叉滑移带;拉伸裂纹在晶内滑移带及晶界处萌生,并主要沿滑移带扩展。欠时效状态下,δ’相的析出量增多,使共面滑移加剧,交叉滑移带难于形成;裂纹除沿晶界扩展外,也有少部分沿滑移带扩展。在达到峰时效以后,交叉滑移带消失;裂纹在三角晶界处萌生并沿晶界扩展。
Deformation and fracture behaviors of an Al-2.56Li-1.29Cu alloy were examined in details by in situ SEM observation in tension mode.The results show that the main precipitate is δ'phase when the alloy is quenched and/or aged at 190℃.In the as-quenched condition,straight slip bands and cross slip bands are shown on the surface of specimens after tensile stress has reached the yield stress;the tensile microcracks are formed in intragranular slip bands or at grain boundaries and extended mainly in slip bands.In the under-aged condition,the amount of phase precipitates are planer slip tend- ency is enhanced,leading to a difficulty in forming cross slip bands,Some tensile microcracks propagate along slip bands apart from that the microcr- acks extend intergranularly.After peak aging,the cross slip bands disappear, and the microcracks are formed at triple points of grain boundaries and ext- end intergranularly.With increasing the aging time,the mods of tensile fracture surface changes gradually from dimpled-intragranular type to the intcrgranular type having slip steps and dimples on the fracture surface.
关键词
AlLi合金
拉伸
断裂
扫描
电镜
Al-Li alloy
tensile deformation
fracture behavior
in situ SEM observation
