Microstructure Evolution during Rolling of AZ31 Magnesium Alloy under Decreasing Temperature

摘要

Strength and ductility are desired characteristics in sheet metals for applications in the automobile industry. Such characteristics are developed during processing of sheet metal from as cast ingot or plate to sheet gauge, primarily by rolling. It is important to understand the evolution of sheet microstructure through the rolling process in order to develop the desired sheet characteristics. In this work, an as-cast AZ31 magnesium alloy plate with coarse grains was hot rolled from a thickness of 5 mm to a final sheet thickness of 1.1 mm. The reduction was achieved in six passes performed at successively lower quasi-isothermal temperatures of 450, 400, 350, 300, 250, and 200°C. Such a rolling process is associated with different deformation mechanisms as the temperature changes, which influence the microstructure evolution. It is found that recrystallization through necklacing dominates at high temperatures, whereas twinning based processes dominate at low temperatures. The understanding developed in here will help devise suitable rolling processes for magnesium sheet with desired characteristics, and in turn help design more formable and lower cost magnesium sheet.