Effects of Different Heat Treatments on Mechanical Properties and Corrosion Resistance of Al-7.95Zn-1.84Mg-0.65Cu Aluminum Alloy

不同热处理对Al-7.95Zn-1.84Mg-0.65Cu合金力学性能和耐腐蚀性能的影响

School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China

Received: 4 September 2019

Abstract

The effects of retrogression and re-aging(RRA) heat treatment on the mechanical properties and corrosion resistance of Al-7.95Zn-1.84Mg-0.65Cu aluminum alloy were investigated by hardness and tensile tests, as well as intergranular corrosion and transmission electron microscopy (TEM). The results show that the Al-7.95Zn-1.84Mg-0.65Cu alloy can obtain better hardness than the single-stage peak aging (T6) process after RRA process (120℃/24 h+200℃/10 min+120℃/24 h). At the same time, the tensile strength is 528.37 MPa, with 13.73% elongation and 29.4% increase in strong plastic product. The electrical conductivity is 40.47% IACS, the intergranular corrosion depth is only 59.43 μm, and the exfoliation corrosion grade is EA. The test results of transmission electron microscopy showed that the η' phase with larger size, greater strengthening effect and more obvious contrast is found in the alloy crystal after RRA treatment, and grain boundary precipitates (GBPs) become more discrete and coarser and precipitation-free precipitated zone (PFZ) becomes wider.

摘要

通过硬度和拉伸实验以及晶间腐蚀和透射电镜（TEM）重点研究了回归再时效（RRA）热处理对Al-7.95Zn-1.84Mg-0.65Cu铝合金力学性能和耐蚀性的影响。研究结果表明，相比于单级峰值时效（T6）工艺，经RRA工艺（120℃/24 h+200℃/10 min+120℃/24 h）处理后，Al-7.95Zn-1.84Mg-0.65Cu合金能够获得较高的硬度，同时抗拉强度达到528.37 MPa，伸长率为13.73%，强塑积提高了29.4%；电导率为40.47% IACS，晶间腐蚀深度仅为59.43 μm，剥落腐蚀等级为EA级。透射电镜结果表明，RRA处理后合金晶内析出尺寸较大、衬度更加明显、强化效应大的η'相，晶界析出相呈现不连续分布，晶界析出相更加粗大，并形成了更宽的无沉淀析出带。