Observation of Microstructural Characteristics on the Formability for AA 7075 Alloy Sheets Under Warm Forming Conditions

¹ Metal Processing R & D Department, Metal Industries Research and Development Centre, 1001 Kaonan Highway, 81160 Kaohsiung, Taiwan
² Department of Mechanical Engineering, National Cheng Kung University, 1 University Road, 701 Tainan, Taiwan

^* Corresponding author: rina1102@mail.mirdc.org.tw

Abstract

Various warm forming processes for AA 7075 alloy sheets integrate pre-aging, optimized process parameters, and paint bake treatment to enhance formability while minimizing strength loss. Previous studies link these improvements to matrix precipitates (MPts) characteristics, but mainly focus on post-formed strength rather than formability under warm conditions. This study evaluates the formability of AA 7075 sheets subjected to peak aging, pre-aging, and W-temper using isothermal warm tensile and limit dome height tests. Microstructural features before forming were analysed via transmission electron microscopy and small-angle X-ray scattering. The correlation between microstructural characteristics and formability was then investigated. Results indicate that the product of MPts volume fraction and average radius (f_vR_avg) has a greater effect on formability than MPts spacing (S_p) in conditions with significant strength differences. This is attributed to the dominant influence of deformation resistance over dynamic recovery, especially when MPts are shearable.