Corrosion and hardness properties of retrogression‐formed and warm‐formed AA7075 sheet

Abstract

AbstractTo achieve combined formability and strength in high‐strength precipitation‐hardened aluminum automotive sheets, different forming path used with fast and slow forming technology has been proposed. This study reports hardness and corrosion properties from two elevated‐temperature forming techniques, retrogression forming (RF) and warm forming (WF), employed on AA7075 alloy sheets. Parameters such as optimal pre‐aging, re‐aging, WF, and RF temperature and time were determined. In the retrogression‐formed (R‐F) sheets, initial retrogression treatment of peak‐aged (i.e., T6) temper resulted in significant loss of properties, but final re‐aging step recovered most. When traditional peak‐aging treatment was used to re‐age R‐F sheets, their T6 hardness and corrosion properties were restored to 95%–97% and 86%, respectively, while re‐aging R‐F sheets using industrial post‐forming paint‐bake treatment restored their T6 hardness and corrosion properties to 87%–92% and 78%–79%. In the warm‐formed (W‐F) sheets, increasing pre‐aging temperature and time resulted in increasing properties, and properties of the best W‐F samples matched the R‐F samples. In addition, shorter‐time forming did not significantly reduce properties of formed part, encouraging the use fast‐forming technology. Overall, these findings show that sheets subjected to RF and WF techniques can possess T6 properties in formed parts.