Investigation On Microstructures And Tensile Mechanical Properties Of Mg-Zn-Y-Zr Alloys

In this work, the effects of Zn content on the microstructures and mechanical properties of as-cast and as-extruded Mg-xZn-5Y-0.6Zr alloys (x=2,5,8and13wt.%) have been investigated. Alloys were extruded into plates with an extrusion ratio of12at380℃. For the uniaxial tensile tests, specimens were machined from the extruded plates in three different orientations with the tensile axis parallel, perpendicular and45°aligned to the initial extrusion direction (ED), respectively. Besides, the low-cost Mg-4.45Zn-0.46Y-0.76Zr alloy was deeply investigated. The results show that:1. Both ultimate tensile strength (UTS) and elongation decrease with the increase of Zn content in as-cast Mg-xZn-5Y-0.6Zr alloys, while the instance of yield strength (YS) is just the reverse. It can be concluded the YS closely depends on the grain size, while UTS and elongation closely depend on the volume fraction of eutectic compound (a-Mg+W-phase).2. With the increase in Zn content, the YS and UTS of as-extruded Mg-xZn-5Y-0.6Zr alloys increase gradually, while the elongation decreases in all three directions. The YS is highest in the ED and decreases towards the TD. Along the ED, the UTS is highest and the elongation is lowest, while for samples along the45°, the instance is just the reverse.3. The as-extruded Mg-4.45Zn-0.46Y-0.76Zr alloy has a good tensile mechanical property. For extruded plate, the UTS of ED sample is331MPa and YS is278MPa with an elongation of12.3%; the UTS of45°sample is285MPa and YS is220MPa with an elongation of23.3%; the UTS of TD sample is304MPa and YS is212MPa with an elongation of16.0%. For extruded rod, the UTS of ED sample is352MPa and YS is287MPa with an elongation of17.9%.4. The strength of the as-extruded Mg-4.45Zn-0.46Y-0.76Zr is influenced through the combination of:(1) dynamic recrystallization (DRX);(2) dynamic precipitation and (3) texture. A large amount of fine precipitates due to dynamic precipitation suppress DRX inside the grains, resulting in a partially recrystallized structure and forming a mixed/bimodal grain structure. Texture influences anisotropy of as-extruded plate through changing Schmid factor, resulting a change of plastic deformation mechanism.