Experimental formability evaluation for aluminium alloy sheets under hot stamping conditions

The process of Hot Form and Quench for aluminium alloys, known as HFQ®, has been developed and applied to manufacture lightweight, high-strength engineering panel components in the automotive industry. However, formability evaluation for the alloys under hot stamping conditions is challenging. In this study, a recently developed biaxial testing method has been applied to aluminium alloy AA6082 for formability evaluation at temperatures ranging from 440–510 °C and at a strain rate of 0.1 s-1. This method involves heating cruciform specimens via the resistance heating system in the Gleeble, and deforming them until fracture via a customised biaxial tensile rig which transfers a uniaxial force into biaxial forces. The location for welding thermocouples on cruciform specimen surface for temperature feedback control in the Gleeble is investigated. Furthermore, temperature nonuniformity within the gauge area of cruciform specimens is quantified, and biaxial tensile tests on the specimens are carried out under different conditions. Both the limit strains at the onset of necking and at fracture are determined, and their dependency on the deformation conditions is analysed. It is found that the biaxial testing method is applicable to AA6082 for formability evaluation under hot stamping conditions. In addition, the limit major strains vary with the strain state, but exhibit a minor dependency on the temperature in the range investigated.