An investigation on microstructure, texture and formability of AZ31 sheet processed by asymmetric porthole die extrusion

This paper provided an effective plastic deformation technique, asymmetric porthole die extrusion, for fabricating AZ31 magnesium alloy sheets. Three kinds of asymmetric porthole extrusion dies were designed and entitled as APE-45, APE-60 and APE-90 die in terms of asymmetric porthole die angle, respectively. The effect of different APE processes on the microstructures, texture evolutions and mechanical properties of AZ31 sheets was investigated at room temperature. For comparison, conventional extrusion (CE) and symmetric porthole die extrusion (PE) were also conducted on processing AZ31 sheets. Shear deformation induced by APE declined the grain size and promoted a broad angular distribution of basal planes in the APE sheets compared with the CE and PE sheets. Especially, the APE-90 sheet obtained finest grain size of 5.2 µm and made basal planes tilted towards the extrusion direction by ~ 21° rotation in the sheet plane. With increasing asymmetric porthole die angle, the volume fraction of recrystallized grains gradually increased, resulting in the decrease of basal pole intensity. Due to the increased activity of basal slip, APE sheets exhibited the decrease in yield strength and r-value and increase in elongation to failure, especially for the APE-90 sheet. The improved formability of the APE sheets was attributed mainly to texture weakening. The APE-90 sheet exhibited the highest index Erichsen value and improved by ~ 74% and ~ 94% compared to the CE and PE sheets, respectively. Consequently, microstructure-texture control induced by APE could enhance the room-temperature stretch formability of AZ31 sheets.