Refined microstructure and dispersed precipitates in a gradient rolled AZ91 alloy under pulsed current

Abstract

Pulse current assisted treatment has gained more attention in metallic materials, which is efficient and energy-saving, as compared with traditional heat treatment. However, the microstructural evolution of magnesium alloys with varied pre-deformation under pulsed current is still unclear. In this work, AZ91 alloy is subjected to gradient rolling and pulse current treatment (∼40 s). After gradient rolling, a transition zone from the initial to deformed microstructure was obtained in the sample, and the evolution of phases and twins can be analyzed precisely and continuously. Due to the difference in the Joule heat distribution of pulse current, a large number of fine Mg17Al12 phase are precipitated and dispersed, the precipitation and dissolution process of Mg17Al12 phase occur simultaneously. The region with moderate deformation has the largest recrystallization fraction, and the {101¯1}−{101¯2} double twins and {101¯1} compression twins are the preferred nucleation sites in the early stage of pulse current treatment. The weaken of texture is due to the newly formed grains with non-basal orientations. This work provides a new insight into the microstructural control of pre-deformed magnesium alloys under pulse current assisted treatment.