Microstructure and temperature monitoring during the hot rolling of AZ31

Abstract

This study details the microstructural evolution during hot rolling of AZ31 alloy sheet using a pilot-scale rolling mill. The aim is to understand the deformation mechanisms leading to grain refinement under industrial processing conditions and to design and optimize the hot rolling schedule for AZ31 in order to produce sheet with a fine and homogeneous microstructure. The study examined three different hot rolling temperatures, 350, 400, and 450°C, and two rolling speeds, 20 and 50 rpm. A total thickness reduction of 67% was obtained using multiple passes, with reductions of either 15% or 30% per pass. It was found that the microstructure of the AZ31 alloy was sensitive to the rolling temperature, the reduction (i.e., strain) per pass and the rolling speed (i.e., strain rate). The results show that the large cast grain structure is broken down by segmentation of the cast grain through localized deformation in twin bands, where dynamic recrystallization occurs in these bands as well as at the grain boundaries (necklacing).