Effect of pulsed electric current on dissolution of Mg17Al12 phases in as-extruded AZ91 magnesium alloy

In this study, the tensile deformation behavior of as-extruded AZ91 magnesium alloy under pulsed electric current has been investigated based on microstructural observations. The flow stress decreased and the elongation increased remarkably on applying electric current in comparison with non-pulsed tensile test at both room temperature and at 70°C. The results of EBSD and EDS analysis showed that dissolution of the Mg17Al12 phase obviously occurs during pulsed tensile test due to thermal effect caused by Joule heating and athermal effect of electric current. To distinguish the athermal and thermal effects of electric current, the induction heat treatment (IHT) that follows the temperature cycle measured during pulsed tensile test was carried out using a dilatometer, which could control the temperature of specimen by an induction heater in a vacuum. Additionally, electropulsing treatment (EPT) was conducted and compared with the conventional heat treatment (CHT) under the same condition. The fraction of Mg17Al12 phase after pulsed tensile test and EPT was obviously lower in comparison with IHT and CHT, respectively. The results prove that applying electric current accelerates dissolution of Mg17Al12 phase in as-extruded AZ91 alloy with a distinct effect from Joule heating during deformation. It is proposed that electrically-assisted manufacturing (EAM) technique can improve the efficiency of forming process for as-extruded AZ91 alloy.