Formability and strengthening mechanism of solution treated Al-Mg-Si alloy sheet under hot stamping conditions

Aluminum alloy hot stamping has been developed to improve formability and avoid thermal distortion by combining hot forming and quenching in one operation in recent years. In order to investigate the effects of heating temperature on formability and strengthening of a solution treated Al-Mg-Si alloy sheet, uniaxial tensile test, deep drawing test and free bulging test were carried out at temperatures ranging from 25 to 500 °C. The corresponding strengthening behavior was reflected by Vickers hardness measurement and microstructure was observed to clarify the strengthening mechanism with electron backscattering diffraction and scanning electron microscope methods. It was found that the fracture strain and limiting bulging height increased significantly until the temperature was elevated to 400 °C. The limiting drawing ratio increased as temperature rose to 200 °C and decreased afterwards. The hardness changed with temperature increasing, two peak hardness appeared at 200 and 500 °C. The maximum hardness could arrive at 115 HV. Formation of coarse β′ precipitates resulted in the decrease in hardness at temperatures ranging from 250 to 450 °C. Enhanced formability and strength were obtained simultaneously at 200 and 500 °C, either of which can be chosen as appropriate forming temperatures for hot stamping.