Influence of process parameters on tribological behaviour of AA7075 in hot stamping

The paper presents the results of recent experimental and numerical investigations on the adhesive onset in AA7075 hot stamping, in order to evaluate the influence of the material thermal treatment and the main process parameters. Solid graphite lubrication was investigated for both the solubilized and the T6 material conditions by means of strip drawing tests in the temperature range 200-450 degrees C varying the normal contact pressure up to 10 MPa and the sliding velocity up to 50 mm/s. The results show that the friction coefficient presents an initial decrease as the temperature increases, followed by adhesion phenomena at the highest temperatures with material transfer to the dies. Such behaviour was explained by using a micro-scale FE model showing that the local temperature in proximity of the roughness peaks may locally influence the material strength causing the adhesive wear onset.