室温多道次ECAP变形对7075铝合金组织性能及沉淀相分布的影响

Effect of room temperature multi-pass ECAP deformation on mechanical properties and precipitation phase distribution of 7075 aluminium alloy

本文采用扫描电镜(SEM)、X射线衍射仪(XRD)和高分辨透射显微镜(HRTEM)研究了等径角挤压(ECAP)变形对7075铝合金显微组织、力学性能、沉淀相分布及析出行为的影响。经四道次ECAP变形后原始晶粒尺寸由26μm细化至4.5μm,组织分布更加均匀,大角度晶界(HAGB)占比由8.1%提高到48.1%。经过ECAP变形后,变形晶粒逐渐转变为亚结构组织和再结晶组织,位错密度在动态再结晶(DRX)作用下逐渐降低,原始7075铝合金轧制态β-fiber织构转变为C型剪切织构,大块不规则沉淀相粒子逐渐破碎细化,弥散分布在基体中,通过HRTEM晶格条纹、XRD及SAED标定可知7075铝合金基体中主要沉淀相种类为Al_(2)Cu、Al_(2)CuMg和MgZn_(2)相。经过四道次ECAP变形后,7075铝合金显微硬度及强度有着明显提高,其中屈服强度(YS)提高了166.1%。在ECAP过程诸多强化机制中,位错强化对于屈服强度的提升占比最高,细晶强化次之,第二相强化占比最小,三种强化机制对于ECAP过程中7075铝合金基体屈服强度贡献比例为2.33:1.67:1。

The effects of equal-channel angular pressing(ECAP)deformation on the microstructure,mechanical properties,precipitation phase distribution and precipitation behaviour of a 7075 aluminium alloy were investigated by scanning electron microscopy,X-ray diffractometry and transmission electron microscopy.The original grain size was refined from 26μm to 4.5μm,the tissue distribution was more uniform,and the percentage of high-angle grain boundaries was increased from 8.1%to 48.1%.After ECAP deformation,the deformed grains gradually transformed into sub-crystalline and recrystallised microstructure,the dislocation density was reduced by dynamic recrystallisation,the original rolledβ-fibre weave transformed into a C-type shear texture,and the precipitated phase particles gradually broke and refined before being distributed in the matrix.The strength and hardness of the original base material were greatly enhanced by combined second-phase and dislocation strengthening effects,but its plasticity was reduced and a mixed brittle-ductile fracture mode is observed.