Warm Deep Drawability of Peak-Aged 7075 Aluminium Sheet Alloy

Abstract

Aluminium has become the material of choice for lightweight design. Today medium strength 5xxx and 6xxx-series alloys are widely used in automotive sheet components, substituting conventional steel because of their superior strength to density ratios. The use of these alloys results in a reasonable ratio of cost per weight saving and a good compatibility with existing production techniques in terms of forming and joining. High-strength 7xxx-series (AlZnMgCu) alloys offer the potential for further light weighting, but formability at ambient temperature is severely limited without the employment of pre- and post- forming heat treatment processes. A promising approach to improve the formability of the peak-aged 7xxx aluminium alloys is to utilize warm forming at process temperatures below the material’s recrystallization temperature. Extensive research on formability is required to develop useful components of complex shapes out of this material. This study describes the material behaviour of a high-strength EN AW-7075 T6 aluminium alloy (e.g. AMAG TopForm® UHS) in the temperature range of the warm forming. For the isothermal simulation of a cross die shape part the material parameters such as flow curves, Lankford parameters and forming limit curves were obtained by experimental testing in the relevant temperature range. A comparison of the numerical simulation with the experimental results for the critical drawing depths for the heated cross die tool at three different temperatures shows good agreement. The results presented in this study demonstrate the potential of warm forming for the manufacturing of complex components made of peak-aged 7075 aluminium sheet alloy.