Investigation on mechanical behavior and plastic damage of AA7075 aluminum alloy by thermal small punch test: Experimental trials, numerical analysis

Abstract

The hot stamping process has demonstrated its high potential to fabricate complex-shaped automotive panel components with high strength AA7075-T6 (Al-5.37Zn-2.18Mg-1.25Cu) aluminum alloy, which conduces to product customization, cost reduction, and efficiency improvement. However, the damage-induced forming crack at high temperatures is more sensitive to the complicated process parameters. A self-developed thermal small punch test (T-SPT) was introduced to investigate the thermo-mechanical behavior and plastic damage of high-strength AA7075-T6 miniature specimens under elevated temperatures in this research. The mesoscopic damage Gurson-Tvergaard-Needleman (GTN) model was employed to predict the micro-area ductile fracture and to conduct formability prediction. An FEM inverse calibration approach coupled with the response surface method (RSM) and the genetic algorithm was developed to accurately identify the temperature-dependent GTN damage parameters based on a series of uniaxial hot tensile curves. Subsequently, numerical simulations of T-SPT regulated by GTN damage parameters were executed to compare with the experimental results. The effects on the mechanical behavior of critical process factors were further discussed, including the deformation temperature, the loading speed, and the surface friction coefficient. Finally, the GTN damage model was successfully applied to predict the formability and the damage distribution of actual AA7075-T6 B-pillar during the hot forming process. The results reveal that the numerical simulation based upon the GTN model owns high reliability and accuracy within the industrialized hot forming application.