Variations in dynamic recrystallization behavior and mechanical properties of AZ31 alloy with extrusion temperature

Abstract

This study investigates the effects of extrusion temperature on the dynamic recrystallization (DRX) behavior of a Mg–3Al–1Zn–0.3Mn (AZ31, wt%) alloy during hot extrusion and on the microstructural characteristics and mechanical properties of materials extruded at 350 and 450 °C. An increase in the extrusion temperature causes a decrease in the amount of strain energy accumulated in the material during extrusion, because of promoted activation of pyramidal slip and dynamic recovery. This reduced strain energy weakens the DRX behavior during extrusion, which eventually results in a decrease in the area fraction of recrystallized grains of the extruded material. The material extruded at 450 °C has coarser grains and a stronger basal fiber texture than that extruded at 350 °C. As the extrusion temperature increases from 350 to 450 °C, the tensile yield strength (TYS) of the extruded material increases from 191.8 to 201.5 MPa, whereas its compressive yield strength (CYS) decreases from 122.5 to 111.0 MPa; consequently, its tension–compression yield stress ratio (CYS/TYS) decreases from 0.64 to 0.55. The increase in the TYS is attributed mainly to the stronger texture hardening and strain hardening effects of the extruded material, and the decrease in the CYS is attributed to the reduced twinning stress resulting from grain coarsening and texture intensification. The microstructural and textural evolutions of the materials during extrusion and the deformation and hardening mechanisms of the extruded materials are discussed in detail.

Keywords

• Mg–Al–Zn alloy
• Extrusion
• Dynamic recrystallization
• Microstructure
• Yield asymmetry