Fabrication And Mechanical Properties Of Investigation On Wronght Mg-Zn-Ca-Gd Alloys

To overcome the poor deformation ability of magnesium alloys, a high performance wrought magnesium alloy is prepared by adding Zn, Ca, Gd element. Mg-Gd binary alloys, Mg-Zn-Gd ternary alloys and Mg-Zn-Ca-Gd quaternary alloys with different components have been designed and prepared by gravity casting and hot extrusion. The microstructures and mechanical properties of alloys with different components and states have been studied by optical microscope (OM), scanning electron microscope (SEM) and tensile tests. Homogenization treatment process and hot extrusion temperature of Mg-4.0Zn-2.0Gd alloy are researched in this paper. The results show as follows:(1) For the Mg-Gd binary alloys with Gd content of0.1,0.5,1.0,2.0,5.0,10.0wt.%respectively, the crystal morphology of the alloys changes from plane to columnar dendrites, and then to the equiaxial dendrites with the increase of the Gd content. After hot extrusion, the microstructures of Mg-0.1Gd and Mg-2.0Gd alloys are refined. The UTS of Mg-0.1Gd alloy increases from 104.8MPa to197.9MPa, and the elongation increases from7.4%to13.0%. The UTS of Mg-2.0Gd alloy increases from115.9MPa to173.6MPa, and the elongation increases from12.9%to60.3%.(2) With the increase of the Zn content, the grain sizes of as-cast Mg-xZn-2.0Gd (x=1.0,2.0,1.0,2.0,5.0) alloy decrease, and the second phase increases gradually and become continuous. In addition, the YS and UTS of as-cast Mg-xZn-2.0Gd alloy also increase with the increase of the Zn content. While the elongation first increase and then decrease and it reaches the peak as the Zn content is4wt.%. After24h of homogenization treatment at430℃, the microstructures and the mechanical properties achieve to best condition for hot extrusion, but the extrusion speed of2mm/s is not conducive to the DRX.(3) With the increase of Ca content, the grain sizes of as-cast Mg-4.0Zn-xCa-2.0Gd (x=0.1,0.2,0.5,1.0) alloys decrease and the precipitates change from (I+W) phases to (Ca2Mg6Zn3+W) phases, and the Mg content in W phase tapers. After hot extrusion, the grain sizes were refined significantly, while the DRX did not occur completely. By comparing the strength and the elongation of the Mg-4.0Zn-xCa-2.0Gd alloys after extrusion, the as-extruded Mg-4.OZn-0.2Ca-2.OGd alloy has relatively balanced mechanical properties at room temperature.