LC4铝合金超塑性变形过程的显微组织研究

本文用金相显微镜及透射电镜研究了超塑性变形对LC4铝合金显微组织的影响。该合金在超塑性变形过程中,除发生大量晶界滑动及晶粒转动外,扩散蠕变在超塑性变形总量中约占15%。在经过超塑性变形的材料内,晶粒内位错密度很低,而晶界处普遍存在由非固有晶界位错规则排列而成的位错群列。这种非固有晶界位错能在超塑性变形过程中以滑移-攀移的方式沿晶界运动,其滑移分量导致晶界滑动,其攀移分量导致扩散蠕变,可协调晶界滑动产生的变形。在超塑性变形后期,在扩散蠕变所产生的晶界旁的无沉淀区内,观察到了自晶界上大粒子处产生的棱柱位错环,导致试样最终断裂的空洞的形核与这种棱柱位错环有关。

A Microstructural Study of Superplasticity in LC4 Aluminum Alloy

By means of light and transmission electron microscopy, theeffect of supperplastic deformation on the microstructure of a finely-grainedLC4 aluminum alloy has been studied. Metallographic studies indicated that during superplastic deformation,in addition to extensive grain boundary sliding and grain rotation, diffu-sional creep occured, and the contribution from diffusional creep to thetotal superplastic strain is about 15%. Transmission electron microscopicstudies revealed that in materials deformed superplastically, the grainswere relatively dislocation free compared with the grain boundaries whereextrinsic grain boundary dislocations were regularly arranged into arrays.The extrinsic grain boundary dislocations could move along the grain boun-daries by a glide-climb process during superplastic deformation. The glidecomponent of the motion led to grain boundary sliding, and the climb compo-nent of the motion led to diffusional creep which could accommodate thegrain boundary sliding strain. In the latter stage of superplastic deforma-tion, prismatic dislocation loops created from large particles at grain boun-daries were observed in precipitate-free zones adjacent to the grain boun-daries caused by diffusional creep. The nucleation of cavities which led tofracure of the specimens is considered to be related to the prismaticdislocation loops.