Friction Stir Welding Process Development of AA7075 for Hot Stamping Applications

Abstract

In order to compete with advanced high strength steels (AHSS) such as dual-phase (DP) or temperature induced plasticity (TRIP) in structural parts, some automotive manufacturers are looking to introduce high strength aluminum alloys that have high peak-aged mechanical properties like AA7075. Formability of these high strength aluminum alloys is possible through hot stamping. Hot stamping refers to simultaneously forming and quenching a blank that is initially at an elevated temperature. Material efficiency can be obtained by using tailor welded blank sections which could lead to weight reductions between 10 and 12%. Friction stir welding (FSW), as a solid-state welding process, has already been proven suitable without hot cracking issues when welding AA7075. However, abnormal grain growth (AGG) issues arise when post-weld operations at high temperature are required such as solution heat treatment or hot stamping operations. This paper details the development of FSW process parameters which will be adapted to hot stamping to effectively join tailor welded AA7075 blanks.