Effect of Grain Size on Adiabatic Shear Sensitivity of AZ31 Magnesium Alloys

The adiabatic shear sensitivity of AZ31 magnesium alloys with different grain sizes under high-strain-rate deformation was investigated using a split Hopkinson pressure bar at 2000s(-1) and a hat-shaped specimen at 150 degrees C. The microstructure of the forced shear regions was characterized via optical microscopy, scanning electron microscopy, electron back-scattered diffraction, and transmission electron microscopy. The microhardness across the forced shear region after high-strain-rate deformation was investigated through Vickers hardness testing. The results show that the adiabatic shear sensitivity of AZ31 magnesium alloys decreases with decreasing grain size, while the width of the adiabatic shear band (ASB) increases with decreasing grain size, and a diffused shear band is formed in the forced shear region when the grain size is reduced to 3 mu m. From the center to the edge of the forced shear region, the microstructure changes from equiaxed grains, to fine grains, and eventually to the matrix, which reflects a gradual variation in the grain size. The fine grains in the ASB cause its microhardness to be significantly higher than that of the surrounding microstructure. The microvoids in the ASB grow and connect with each other along the shear direction, finally resulting in macrofractures.

Automated summary

The adiabatic shear sensitivity of AZ31 magnesium alloys decreases with decreasing grain size, while the width of the adiabatic shear band (ASB) increases with decreasing grain size. A diffused shear band is formed in the forced shear region when the grain size is reduced to 3 μm. The microstructure in the forced shear region changes from equiaxed grains, to fine grains, and eventually to the matrix, reflecting a gradual variation in grain size. The microhardness of the ASB is significantly higher than that of the surrounding microstructure due to the presence of fine grains.