CANCELLED - Ultrahigh Strength Mg-Gd-Y-Zn-Zr Alloy Processed By Hot Extrusion

Mg-8.2Gd-3.8Y-1Zn-0.4Zr (wt%) ingot with 280 mm in diameter and 2940 mm in length was produced by direct-chill casting. The homogenized ingot was extruded into rods of 60 mm in diameter through a mold with three holes at 400^oC with an extrusion ratio of 8:1. The ageing treatment of the extrusion rod was performed at 200 ^oC for different periods. The microstructures, textures and mechanical properties of the as-extruded and peak-aged alloys were investigated. A large number of β′phases were observed in the peak-aged alloy, accompanied with the decrease of the volume fraction of LPSO phases. A basal fiber texture and an unusual texture component with basal planes perpendicular to the extrusion direction were found in the as-extruded alloy, and the basal fiber texture was strengthened after ageing treatment. The peak-aged alloy exhibited a tensile yield strength (TYS), an ultimate tensile strength (UTS) and an elongation to failure of 416 MPa, 482 MPa and 9.3%, respectively. The superior strength of the peak-aged alloy was mainly attributed to the precipitation of fine β′phases, the remaining LPSO phases and the texture modification.