Effects of the extrusion parameters on microstructure, texture and room temperature mechanical properties of extruded Mg–2.49Nd–1.82Gd–0.2Zn–0.2Zr alloy

Abstract

Microstructure, texture, and mechanical properties of the extruded Mg–2.49Nd–1.82Gd–0.2Zn–0.2Zr alloy were investigated at different extrusion temperatures (260 and 320°C), extrusion ratios (10:1, 15:1, and 30:1), and extrusion speeds (3 and 6 mm/s). The experimental results exhibited that the grain sizes after extrusion were much finer than that of the homogenized alloy, and the second phase showed streamline distribution along the extrusion direction (ED). With extrusion temperature increased from 260 to 320°C, the microstructure, texture, and mechanical properties of alloys changed slightly. The dynamic recrystallization (DRX) degree and grain sizes enhanced as the extrusion ratio increased from 10:1 to 30:1, and the strength gradually decreased but elongation (EL) increased. With the extrusion speed increased from 3 to 6 mm/s, the grain sizes and DRX degree increased significantly, and the samples presented the typical $<2{\bar 1}{\bar 1}1>-<11{\bar 2}3>$ rare-earth (RE) textures. The alloy extruded at 260°C with extrusion ratio of 10:1 and extrusion speed of 3 mm/s showed the tensile yield strength (TYS) of 213 MPa and EL of 30.6%. After quantitatively analyzing the contribution of strengthening mechanisms, it was found that the grain boundary strengthening and dislocation strengthening played major roles among strengthening contributions. These results provide some guidelines for enlarging the industrial application of extruded Mg–RE alloy.

Keywords

Mg–rare earth alloys / extrusion temperature / extrusion ratio / extrusion speed / strengthening mechanisms