An extrusion-welding criterion of magnesium alloy considering interfacial void shrinkage driven by plastic deformation and atomic diffusion

Abstract

This study is aimed to develop a new criterion to predict the solid-state welding quality of magnesium alloy during the porthole die extrusion of hollow profiles. In this criterion, the mechanism of interfacial void shrinkage of magnesium alloy during the extrusion welding is considered, including the plastic deformation of rough interfaces and the atomic diffusion driven by the hydrostatic pressure gradient. The developed criterion is validated by the combined extrusion-welding experiments of magnesium alloy and the corresponding numerical simulations. The results indicate that the bonding strength of magnesium alloy increases with growing billet temperature and decreasing the extrusion stem speed. A sound weld seam with a strength higher than 316 MPa is formed by the porthole extrusion when the billet temperature of Mg-Al-Zn-RE alloy is above 350 °C (623 K) and the extrusion speed is below 16.67 mm/s. Compared with other existing criteria, the developed criterion is more reliable in predicting the extrusion-welding quality of magnesium alloy.