Influence of heat treatment and pre-straining on dynamic precipitation and creep behavior of AZ91-0.5Y magnesium alloys

Abstract

Herein, the effect of heat treatment and pre-straining on dynamic precipitation and creep properties of an extruded AZ91-0.5Y magnesium alloy is systematically investigated. Four kinds of samples processed by solid solution (SS), aged after solid solution (SA), pre-strained after solid solution (SP) and subsequently aged (SPA) were prepared. The creep tests were conducted at different temperatures, ranging from 150 to 180 °C, under various applied stresses, ranging from 50 to 70 MPa. The results reveal that the highest creep resistance is found in the SP sample, followed by SPA and SS samples, and the lowest creep resistance is exhibited by the SA sample. The microstructural results clarify that the creep resistance can be related to the type and density of dynamically precipitated Mg17Al12 phase. For the SS and SA samples, a high volume fraction of lamellar structures of Mg17Al12 is formed during creep test, making basal <a> slip and prismatic <a> slip as the dominant creep mechanisms. The twins introduced by the pre-straining contributed a high volume fraction of spherically-shaped Mg17Al12 phase, making pyramidal <c+a> slip and twinning as the dominant creep mechanisms for SP and SPA samples. The twinning and high volume fraction of spherically-shaped Mg17Al12 phase are the reasons for the optimal creep properties of the SP sample.