Texture evolution of AZ31 magnesium alloy sheets during warm rolling

Abstract

The purpose of this study was to examine the microstructure and texture evolution of a twin roll cast AZ31 magnesium alloy after multi-pass warm rolling in a temperature range from 233 to 248°C. Reduction per pass was kept constant at about 10% and the total reduction was 98.2% after 33 pass steps with a change of sheet thickness from initially 2.85mm down to 50μm. The rolled sheets exhibited a fairly strong basal texture with an intensity of 17–21 multiples of random distribution (MRD) in the initial stages (with a thickness above 0.47mm) due to the lower rolling temperatures. The basal texture intensity decreased to 13–15 MRD in the later stages (with a thickness below 0.3mm) due to the occurrence of dynamic recrystallization at slightly higher rolling temperatures to balance out the demand of rolling force. The basal pole in the thicker sheets spread slightly along ±TD with an ellipse shape mainly due to the activation of 〈a〉 prismatic slip and the occurrence of shear bands, while the splitting of basal pole in the thinner sheets was observed to be along the RD with a tilting angle of about ±10°. This was attributed to the activation of 〈a+c〉 pyramidal slip. The average grain size in the thinner sheets in the later stages during the multi-pass rolling decreased almost linearly with increasing number of rolling steps. This could be explained via a change in the Zener–Hollomon parameter which was associated with the strain rate affected by the sheet thickness during rolling at a constant percent reduction.