Study On Microstructure And Mechanical Properties Of Quasicrystal Reinforced Mg-Zn-Y-(X) Alloys

As quasicrystal was used to improved the strength and ductility of magnesium alloys effectively, Quasicrystal reinforced magnesium alloy was high-profile. Compared with conventional high-strength magnesium alloys, quasicrystal reinforced magnesium could still maintain a certain ductility at a high intensity. We can introduce traces of alloying element into quasicrystal reinforced magnesium alloy to make the combination of quasicrystal reinforcing and solution strengthening, which is a new way to develop high-strength magnesium alloy.In this paper, the Mg-6xZn-xY alloys were firstly investigated. Then the Mn, Cu, Zr elements were added into Mg-6xZn-xY alloy respectively, and in another way Mn and Cu elements were added together into the alloy to develop high strength and toughness alloys with low content alloying elements. The effect of content of different alloying elements on the Mg-6xZn-xY alloys microstructure and mechanical properties was Studied. Also, the effect of Mn, Cu and Zr elements on the microstructure and mechanical property were studied respectively. In the meanwhile, the comparison of the microstructure and mechanical properties under special and common conditions were made to study the effect of the process.The conclusions of this paper are as follows:1) Microstructure and mechanical properties of casting and extrusion Mg-6xZn-xY(x= 0.25,0.5,0.75,1,1.25,1.5) alloy were investigated in this paper. Influence of the size, content and distribution of I-phase to the mechanical properties of the alloy was also studied. The results show that with the increase of the content of Zn, Y elements, the I-phase gradually increased. The Ⅰ-phase particle size ranged from 0.1 μm～0.3 μm and were well-distributed in the extruded Mg-6Zn-1Y alloy. The a-Mg grain size of the alloy is about 2.9μm. The tensile strength of this alloy is about 373Mpa with the Elongation of 13.5%. Ⅰ-phase is the determinant factor of microstructure and mechanical properties of Mg-6xZn-xY alloy.2) The changes in the microstructure and mechanical properties by adding element Mn and the composite strengthening of Ⅰ-phase strengthening and Mn solid solution strengthening were studied. The results show that the preferred addition amount of Mn is less than its solubility in the a-Mg(about O.lat.%). The tensile strength of Mg-3Zn-0.5Y-0.1Mn alloy is 329Mpa with an elongation of 19%.3) Research on the changes in the microstructure and mechanical properties by adding element Cu was carried out, and the composite strengthening of I-phase strengthening and Cu solid solution strengthening was studied. The results show that after element Cu was added into the alloy, it mainly enriched in I-phase around. And it will cause an increase of the layer thickness ratio of I-phase and a-Mg. Excessive content of Cu would lead to I-phase lamellar coarsening, leading to I-phase particle agglomeration in extruded alloy. It is harmful to the mechanical properties of the alloy. The preferred dosage of element Cu in I-phase reinforced Mg-Zn-Y alloys is about 0.2at.%. The tensile strength and yield Strength of Mg-3Zn-0.5Y-0.2Cu alloy is 334Mpa and 262Mpa with an elongation of 21%.4)The addition of Zr made the way of strengthening changed, for the element Zr cause the grain size finer and fine grain strenthening plays the leading role than the I-phase strengthening. The escessive content of Zr element would cause sencondary resrystallization during the extruding process. The moderate addition of element Zr is 0.03at.%. The tensile strength of Mg-3Zn-0.5Y-0.03Zr alloy is 380MPa, and the YS is more than 350MPa, while the ductility is maintaining 24%.5) After Mn and Cu elements were added into the quasicrystal reinfored Mg-Zn-Y alloy, the changes of microstructure and mechanical properties of the alloy is both small. But the effect of the additon of Mn and Cu elements on the yield strength(YS) is conspicuous. The the Ys of Mg-3Zn-0.5Y-0.04Mn-0.06Cu(at.%) is 263Mpa, which is 15% more then Mg-3Zn-0.5Y alloys.6) Before the Mg-3Zn-0.5Y alloy was extrued, it was holding at 480℃ for 20h. This process lead to the ductility of the extruded alloy is ultra-high, i.e.42%, but the tensile strength is only 188Mpa, slightly higher then the strength of the as-cast Mg-3Zn-0.5Y alloy.7) With the increase of cooling rate, the lamellar I-phase in the eutectics became thinner under a certain condition. At the same time, a mass of divorce eutectic occurred.