Tensile and fatigue properties of twin-roll-cast az31 magnesium alloy strips with different thicknesses

This study investigates the microstructure, tensile properties, and high-cycle fatigue resistance of twin-roll-cast Mg-3Al-1Zn (wt%) alloy strips with thicknesses of 1 mm, 1.5 mm, and 3 mm. The investigation results reveal that the 1-and 1.5-mm-thick strips show a fully dynamically recrystallized (DRXed) microstructure consisting of fine equiaxed DRXed grains, whereas the 3-mm-thick strip shows a partially DRXed microstructure containing very coarse elongated unDRXed grains because of the insufficient strain imposed during twin-roll casting. The inhomogeneous microstructure of the 3-mm-thick strip leads to a large deviation in its tensile elongation. The average grain size of the strips increases with increasing strip thickness, which results in reductions in both their tensile strength and their ductility because of the weakened grain-boundary hardening effect and the promoted formation of undesirable twins, respectively. The high-cycle fatigue resistance in the stress regime with finite fatigue life is similar for all three strips, but the fatigue strength with infinite fatigue life decreases from 175 MPa to 140 MPa as the strip thickness increases from 1 mm to 3 mm. The fatigue strength (FL) increases linearly with increasing yield strength (YS) according to the relationship FL = -199.5 + 2.03·YS.