Microstructure And Properties Of Hot Extruded Mg-Zn-Y-Ca Alloy And Its Composites

In this study,Mg-6x Zn-xY-0.2Ca?wt.%??x=0.4,0.6,0.9?alloys were fabracted by adjusting the content of Zn/Y simultaneously,and hot extrusion was carried out at the same time.The effects of different Zn/Y contents on the microstructural evolution of as-cast Mg-Zn-Y-Ca alloys were studied.Besides,the effects of hot extrusion process on Mg-Zn-Y-Ca alloys were systematically studied.The effects of difffrent Zn/Y content on the mocristructure and mechanical properties of extruded Mg-Zn-Y-Ca alloys during extrusion process were discussed.Then,2vol.%SiC_p was added to these alloys,the effects of the addition of SiC_p in Mg-Zn-Y-Ca alloys were investigated.The results showed that the second phase of the as-cast Mg-Zn-Y-Ca alloy is icosahedral phase.With the increase of Zn/Y content,I-phase grows up and changes from granular to semi-continuous gradually,meanwhile,the volume frcation of I-phase increases.After homogenization at 400°C for 8 hours,the size and volume fraction of I-phase increased slightly.With the addition of SiC_p,the grain size refined obviously,part of Y elements was easily segregated in the vicinity of particles,and the second phase in the as-cast microstructure were I-phase and newly-formed MgZn₂ phase,the volume fraction of the second phase increases with the increase of Zn/Y content.After the homogenization treatment,the MgZn₂ phase solidifies to the matrix.With the increase of extrusion speed,the recrystallized grain size of ZWX-0.6 alloy increases from 1.22?m to 4.76?m,and the volume frcation of recrystallized grains increases from 62.8%to 98.0%.Meanwhile,the volume fraction of precipitates decreases from 11.4%to 2.0%with the increase of extrusion speed,while increases from 0.75?m to 2.99?m,and thevolume frcation of recrystallized grains increases from 60.9%to 92.3%.The volume fraction of precipitates decreases from 11.4%to 2.0%and then increases from 3.5%to 7.5%with the increase of extrusion speed.The<10-10>oriented fiber texture was formed in ZWX-0.6 alloy after extrusion in different extrusion processes,besides,the<11-20>oriented texture was also observed after extrusion at 270?and 0.1mm/s.Moreover,with the increase of Zn/Y content,the size and volume fraction of recrystallized grains decreased at first and then increased,the mechanical properties of yield strength and ultimate tensile strength increased after extrusion,while elongation decreased first and then increased slightly with the increase of Zn/Y content.The optimal strength was obrained when Zn/Y content is 6.After addition of SiC_p,the recrystallization of SiC_p/Mg-6x Zn-xY-0.2Ca?x=0.4,0.6,0.9?composites is almost completed after extrusion.With the increase of extrusion speed,the recrystallized grain size of SiC_p/Mg-3.6Zn-0.6Y-0.2Ca?SiC_p/ZWX-0.6?composites increases from 1.63?m to 4.32?m,and the volume fraction of precipitates decreases from 5.3%to 1.1%with the increase of extrusion speed.The recrystallized grain size of SiC_p/ZWX-0.6 composites increases from0.90?m to 2.50?m with the increase of extrusion temperature,and the volume fraction of precipitates phase increases from 2.5%to 3.5%firstly,and then reduces to 2.2%.Meanwhile,with the increase of Zn/Y content,the texture intensity of three SiC_p/ZWX-0.6 composites after extrusion decreases,YS and UTS increases gradually.Compared with Mg-Zn-Y-Ca alloys,the addition of SiC_p can promote the occurrence of DRX obviously,but it can also inhibit the dynamic precipitation process.When the content of Zn/Y increased from 0.4 to 0.6,the occurrence of DRX was promoted,but when the content of Zn/Y increased further,the DRX process was inhibited.The increase of Zn/Y content can also promote the precipitation.