Effect of process parameters on AA6061/Q345 bimetal composite for hot stamping

Hot stamping is an advanced forming process used in automobile lightweight manufacturing, but it has not been used in the manufacture of bimetal composite parts. In this work, based on the hot stamping forming technology and the advantages of bimetal composite in strength, stiffness and corrosion resistance, the finite element simulation theoretical analysis and test on the hot stamping forming of AA6061/Q345 bimetal composite U-shaped parts were performed. The effect of initial temperature, stamping speed, die gap and pressure holding time on forming quality were investigated. The results show that the initial temperature not only affects the temperature distribution of each layer of the bimetal composite after stamping but also affects the deformation resistance during forming. The increasing stamping speed reduces the contact time between the die and plate rising the plate temperature, but the increasing stamping speed also strengthens the stamping hardening effect in the forming process leading to the stress increase. The die gap affects the contact area between the plate and the die. The increasing gap is beneficial to reduce the temperature difference between different layers. However, an excessive die gap also increases the tensile stress in the plate and affects the forming accuracy. With the pressure holding time larger, the temperature of the formed part becomes low, the residual stress releasing causes the stress to be smaller. According to the analysis of tensile and bending mechanical properties, it is indicated that the formed parts prepared by the optimal parameters obtained by numerical simulations have excellent mechanical properties and formability.