Experimental and numerical study of the warm formability of a 7xxx Al alloy

Performing well-controlled warm formability experiments on metal sheets is a topical industrial challenge as vehicle lightweighting turns to higher strength aluminium alloys. A number of difficulties with warm forming are tackled in this paper using both an experimental and a numerical approach. The sensitivity of the material behaviour to temperature and strain-rate was first studied using tensile testing. It is shown that the strain-rate does not have a significant impact on the material response below 180 °C. At 180 °C the yield stress and the strain hardening are higher at faster strain-rates. Nakazima experiments were then carried out on a forming press to study the formability of the material at different temperatures. The impact of several parameters on the results was investigated in order to conduct and analyse properly warm formability experiments (e.g., friction, filtering methods, etc.). A finite element model was also developed to support this sensitivity study. A comparison between the forming limit diagrams obtained experimentally and numerically is presented.