Microstructures and mechanical properties of friction stir processed Mg-2.0Nd-0.3Zn-1.0Zr magnesium alloy

The effect of Friction stir process (FSP) parameters on the microstructure and mechanical properties of an extruded Mg-2.0Nd-0.3Zn-1.0Zr (wt.%) alloy was investigated in this paper. The alloy was friction stir processed with different passes: single-pass, three-pass and five-pass, under a tool rotation rate of 800 rpm and a traverse speed of 200 mm min−1. FSP results in remarkable grain refinement of the extruded alloy (average grain size ∼3.8 μm as 3 passes) and almost complete dissolution of the Mg12Nd phase in the matrix. With the increase of pass, the average grain size in the stir zone (SZ) is decreased firstly and then increases. The Vikers hardness of SZs in all FSPed samples is higher than that of the parent material (PM). Tensile tests at room-temperature show that the tensile strengths of the stir zones along the FSP advancing direction are slightly lower than those of PM. However, the elongations are remarkably improved from 13.0% for PM to 24.5% for SZ FSPed with three-passes. These improved tensile properties are attributed to the microstructure refinement, dynamic recrystallization and dissolution of the Mg12Nd phase.