An experimental and numerical investigation on the formability of AA7075 sheet in hot stamping condition

Abstract

Formability of aluminum alloys at elevated temperatures are of vital importance to process design and numerical simulation of aluminum hot stamping. In this paper, the hot formability of AA7075 was investigated experimentally and numerically. Firstly, a series of hot uniaxial tensile tests were performed on a Gleeble 3500 thermomechanical simulator to determine constitutive relationships of AA7075 at different temperatures and strain rates. Based on these results, a uniaxial damage model was established, and further extended to a multi-axial continuum damage mechanics (CDM) based model with the consideration of stress state and strain path effects for hot stamping. Good agreement between model fitting and experimental results was achieved. Secondly, hot formability tests were conducted to investigate deformation characteristics at elevated temperatures. Finally, a finite element (FE) model using software ABAQUS with implemented the CDM model via subroutine was established and validated by corresponding experimentations. The developed FE model was utilized to investigate effects of process variables on material deformation and damage evolution in detail. It was found that formability can be improved with decreasing forming temperature and increasing forming speed. In addition, friction has a dominant effect on determining failure location.