Effect of Pass Strain on the Microstructure, Texture and Mechanical Properties of AZ31 Magnesium Alloy Fabricated by High Strain Rate Multiple Forging

Abstract

High strain rate multiple forging (HSRMF) with pass strain ranging from 0.1 to 0.35 was carried out on the AZ31 magnesium alloy, and the microstructure, texture and mechanical properties were examined. The initial grain can be refined through the formation of high density {102} and {101(-)1}-{101(-)2} twins and subsequently twining induced dynamic recrystallization (DRX). The grain refinement of the HSRMFed alloy was affected by the lamellar thickness of the twin. Lower pass strain (Δε = 0.1) during HSRMF leads to the thick twin lamellae and consequently results in coarse DRX grain, meanwhile, an incomplete DRX occurs. While the twin lamellae thickness decreases with increasing pass strain, and a saturate thickness can be achieved with higher pass strain (Δε = 0.16–0.35), which results in the finer DRX structure. Homogeneous DXR structure can be obtained only at a proper accumulated strain (∑Δε = 0.96–1.4) during HSRMF, under lower accumulated strain, the DRX is insufficient, while higher accumulated strain leads to abnormal grain growth. A double peak basal texture was achieved at lower pass strain (Δε = 0.1), which developed into titled basal texture, and the texture intensity increases with the pass strain. HSRMFed alloys with homogeneous fine DRX grain and relatively weak texture show high strength and excellent ductility, therefore, and it is inferred that the optimum pass strain and accumulated strain range are 0.16–0.35 and 0.96–1.4 respectively.