Research on Pre-hardened Hot Formability of 7075-T6 Aluminum Alloy B-pillar

Pre-hardened hot forming is a new process which solves the problem of long hot stamping period of high-strength aluminum alloys. In order to study the hot deformation behavior of 7075-T6 aluminum alloy under pre-hardened hot forming process, the hot tensile tests of 7075-T6 aluminum alloy at different deformation temperature（200-350 ℃） and strain rate(0.01 s^-1-1 s^-1) were carried out by using Gleeble thermal simulator. The flow stress of the aluminum alloy increases significantly with the increase of strain rate and the decrease of deformation temperature. A constitutive model for predicting the thermal deformation behavior of 7075-T6 aluminum alloy was established. Numerical simulation of the pre-hardened hot forming process of the automobile B-pillar was carried out, and the effect of stamping speed, friction coefficient and forming temperature on the formability of the B-pillar was studied by numerical simulation. The results show that the stamping speed,initial temperature of sheet and friction coefficient are basically positive correlated to the maximum thinning rate of sheet metal. The formability of B-pillar can be improved by properly increasing the stamping speed and decreasing the initial temperature of sheet metal. Moreover, too small or too large friction coefficient is easy to cause local wrinkling or tensile defects.