Optimization Of Microstructure And Mechanical Properties Of Mg₉₃Zn₆Y₁ Alloy Reinforced By In-situ Quasicrystals

As the lightest metal structure materials in engineering applications, magnesium alloys were widely used in transportation, 3C products and aerospace fields.However, due to the high temperature properties of magnesium alloys were poor, which made it can not be widely applied in the high temperature parts.In order to improve the properties of magnesium alloys, need to introduce high hardness and thermal stability reinforcement as strengthening phase in magnesium alloys. Compared with magnesium matrix composites reinforced by quasicrystalline particles,magnesium alloy reinforced by in-situ quasicrystals reduced complex preparations such as pre-quasicrystalline particles, handling and join. The preparation was relatively simple and easy to organize large-scale production. To this end, this paper use Mg93Zn6Y1 alloy reinforced by in-situ quasicrystals as the research object,we have studied the DC magnetic treatment, the addition of Cu element, T4 heat treatment process, the casting temperature and cooling rate on the effect of microstructure and mechanical properties of as-cast Mg93Zn6Y1 alloy, the major conclusions were as follows:1) With the addition of the DC magnetic field, in the range of 0 ~ 1.2T,the grain size of as-cast Mg93Zn6Y1 alloy showed decreased and then increased, the effect of refining was best when the magnetic field strength was 0.3T. The grain size on longitudinal section of alloy specimen was significantly larger than on cross section.The strongest peak of x-ray diffraction pattern on cross section was changed when the magnetic field strength was 0.6T, it transfered from(101) to a new lattice plane(201), also there was an other new lattice plane(110). Accompanied by the increase of magnetic field strength, in the range of 0 ~ 1.2T,the diffraction peak value corresponding to(100) lattice plane was gradually increased. The alloy formed preferred orientation on(100) lattice plane. Accompanied by the increase of magnetic field strength,the mechanical properties of as-cast Mg93Zn6Y1 alloy showed increased regularity, and when the magnetic field strength was 1.2T, the mechanical properties of as-cast Mg93Zn6Y1 alloy were best, the tensile strength and elongation were 169 Mpa and 2.8%, compared with those non-magnetic treatment of as-cast Mg93Zn6Y1 alloy,improved by 19.8% and 33.3%, respectively.2) The introduction of Cu have made as-cast Mg-Zn-Y-x Cu alloys generated Mg Zn Cu phase(Mg Cu2 type Laves phase), with the increased of Cu content,the grain size of alloy showed decreased and then increased, and the effect of refining was best when the Cu content was 1.5at%.The mechanical properties of as-cast Mg93Zn6Y1 alloy have improved by the addition of Cu.At room temperature and the elevated temperature, the tensile strength and elongation of as-cast Mg91.5Zn6Y1Cu1.5 alloy were178 MPa,3.8% and 153 MPa,10.6%,compared with Mg93Zn6Y1 alloy,increased by10.5%,40.7% and 26.4%,49.3%, respectively.3) After T4 heat treatment, the microstructure of as-cast Mg-Zn-Y-x Cu alloys mainly consists of primary α-Mg + I-phase + Laves phase. With the increased of Cu content,the tensile strength of as-cast Mg-Zn-Y-x Cu alloys showed decreased and then increased,and the mechanical properties were best when the Cu content was1.5at.%,the tensile strength reached 180 MPa. Compared with the as-cast Mg91.5Zn6Y1Cu1.5 alloy without T4 heat treatment, the tensile strength of as-cast Mg91.5Zn6Y1Cu1.5 alloy after T4 heat treatment only enhanced 2MPa.Thus, the effect of T4 heat treatment process to enhance the mechanical properties of as-cast Mg-Zn-Y-x Cu alloys was not obvious.4) With the increased of pouring temperature, the grain size of the as-cast Mg93Zn6Y1 alloy increased gradually. The tensile strength of the alloy showed increased and then decreased, and when the pouring temperature was 720 ℃, the mechanical properties of Mg93Zn6Y1 alloy were best, the tensile strength and elongation reached 161 MPa and 3.1%, respectively.5) With the decreased of cooling rate, the grain size of as-cast Mg93Zn6Y1 alloy and Mg91.5Zn6Y1Cu1.5 alloy were increased gradually. At low cooling rates, the tensile strength and elongation of as cast Mg93Zn6 Y alloy and Mg91.5Zn6Y1Cu1.5 alloy were only 96 MPa,0.8% and 114 MPa,1.5%,compared with those at high cooling rates,decreased by 39.6%,66.6% and 40%,60.5%, respectively.