Excellent mechanical properties obtained by low temperature extrusion based on Mg-2Zn-1Al-0.2Mn-0.2Ca-0.2Gd alloy

A newly developed low Al containing magnesium alloy, Mg-22n-1Al-0.2Mn-0.2Ca-0.2Gd (wt.%) shows excellent mechanical properties. The alloys with superior high strength and considerable ductility (the maximum of tensile strength reaches 332 MPa and corresponding elongation is 23.1%) were produced by electromagnetic casting and extrusion at relatively low temperatures (110 degrees C, 170 degrees C, 210 degrees C, and 250 degrees C) with an extrusion ratio of 17.4:1. Effects of extrusion temperature on the evolution of microstructure, mechanical properties and extruded texture were investigated by OM, SEM, TEM, and EBSD analysis. The microstructures of the alloy extruded at low temperatures mainly consist of the equiaxed dynamically recrystallized grains, elongated grains, and regions without dynamic recrystallization. And there are only equiaxed dynamically recrystallized grains in the alloy extruded at 250 degrees C. The increasing extrusion temperature results in grain coarsening and strength reduction. When the extrusion temperatures are 110 degrees C and 170 degrees C, the average grain size reaches submicron level of 0.65 mu m and 0.89 mu m, respectively. Because the higher extrusion temperature makes the dynamically recrystallized grains rotate in a favorable direction, the basal texture enhances with the rise of extrusion temperature. The high strength is mainly attributed to the structure of extremely refined grains. High ductility benefits from a large amount of basal slip, activation of non-basal slip, and grain boundary movement under the action of tensile stress. (C) 2019 Elsevier B.V. All rights reserved.