Microstructure And Mechanical Properties Of Mg-Zn-Y-Zr Alloys

Magnesium alloys have the advantages of light-weight, high strength/weight ratio, high stiffness/weight ratio, so it is wildly considered to be the advanced industry alloy in future. Mg-Zn-Zr based alloy is typical high strength magnesium alloy. But its strength is difficult to apply in higher condition.In this dissertation, a new magnesium alloy system Mg-6Zn-χY-0.65Zr(χ=0,1,3,5) is achieved by adding Y and Zr element on the basis of Mg-Zn-Zr. Samples are melted in electric resistance furnace and poured into steel mould by the common casting method. The microstructures, phase composition were systemically investigated by using measurements of OM, XRD, SEM, EDS and the tensile strength and hardness were tested at room temperature.It is shown that the phases in the as-cast Mg-6Zn-0.7Zr alloy are mainly composed ofα-Mg, Mg7Zn3 and MgZn . The precipitates distributed in the grain. The phases in the as-cast Mg-6Zn-1Y-0.7Zr alloy areα-Mg,Mg7Zn3和Mg3Y2Zn3. As the addition of Y ,The phases in the as-cast Mg-6Zn-3Y-0.7Zr alloy areα-Mg, Mg12YZn and Mg3Y2Zn3. The Mg12YZn will increase and the Mg3Y2Zn3 will decrease. The grain boundary appears two kinds of morphology: one is"fish bone", the other is massive. The two kinds of morphology form the continuous eutecticstructure. As the addition of Y,the as-cast strengthening mechanism is increased, then decreased. when content of Y is 3wt% the grains are the most finest. the ultimate tensile strength is 250.4MPa, and yield strength is 125.3 MPa, the elongation is 12.73 at room temperature.After ageing treated, The precipitates distributed in the Mg-Zn-Y-Zr alloy grain.are MgZn′.The phases in the T6 Mg-6Zn-3Y-0.7Zr alloy areα-Mg,MgZn和Mg3Y2Zn3, The grain size is increased. The mechanical properties of the alloys are increased. The brinell hardness of the alloy was increased from 80.3 to 91.2, The max ultimate tensile strength(UTS) and yield tensile strength(YTS) at room temperature are 290.3MPa and 184.3 MPa. The addition of Y can improve the strength and ductility of alloys.