Effect Of YB On Microstructure And Properties Of ZMT613 Magnesium Alloy

Magnesium alloy is one of the lightest structural metal materials in engineering application,and has a wide application prospect.Mg-6Zn-1Mn-3Sn(ZMT613)alloy is a new type of low cost and high performance deformed magnesium alloy with great potential.However,compared with high rare earth magnesium alloy,its absolute strength is low.In order to further improve the properties of the alloy,The effect of Yb on the microstructure and properties of ZMT613 magnesium alloy(as-cast,homogenized,extruded,solid solution,T5 aging and T6 single and double stage aging)was studied by micro characterization(OM,SEM,EDS,DSC,XRD)hardness test and room temperature tensile test.The results are as follows:The second phase in as-cast ZMT613 is continuous network distribution.After Yb element is added,the microstructure of ZMT613-x Yb(x=0.2,0.3,0.5,0.8)alloy is obviously refined,the second phase transition is discontinuous,and a new phase of Mg Sn Yb is formed in the alloy.With the increase of Yb element,the content of Mg Sn Yb phase increases and the content of Mg₂Sn phase decreases gradually.After the optimized two-stage homogenization process(330?/12h+430?/2h),Mg₇Zn₃ phase dissolved into the matrix,and the thermal stability of Mg₂Sn and Mg Sn Yb phases was high,and remained on the matrix.After hot extrusion,the microstructure and properties of ZMT613-x Yb alloy were obviously changed.During extrusion,the alloy recrystallization occurs dynamically,and the grain is refined obviously,and the average grain size decreases with the increase of Yb content.The remaining Mg₂Sn and Mg Sn Yb phases after homogenization were crushed during extrusion and distributed along the extrusion flow line.The properties of extruded alloy can be improved by adding Yb element to a certain extent.Compared with ZMT613 alloy,when Yb element addition is 0.8%,the alloy performance is the best,its YS increased from 221 MPa to 248 MPa,UTS increased from 327 MPa to 348MPa,but the elongation decreases from 13.4%to 10.2%.The better T5 aging process of ZMT613-x Yb alloy is 180?/10h.The microstructure of T5 aging alloy t changed little compared with extruded alloy.After adding Yb element,the properties of T5 aging alloy are improved obviously,among which ZMT613-0.5Yb has the best comprehensive mechanical properties.Compared with ZMT613 alloy,its YS increases from 237 MPa to 268 MPa,and the UTS increases from 315 MPa to 357 MPa,the elongation increased from 10.2%to 12.6%.420?/2h is the best solution process of ZMT613-x Yb alloy,180?/10h is the better T6 single stage aging process,90?/24+180?/6h is the better T6 double stage aging process.The strength of the alloy was not changed but the elongation was increased obviously after adding Yb element to T6 single aging ZMT613 alloy,among which the elongation of ZMT613-0.8Yb alloy was the highest(6.1%),which was about100%higher than that of the base alloy.T6 double aging can effectively exert the aging strengthening effect of Mg-Zn alloy,and the strength of the alloy is further improved.The mechanical properties of ZMT613 alloy can be improved by adding proper Yb element.ZMT613-0.2Yb alloy has the best comprehensive mechanical properties in T6two-stage aging alloy.Compared with ZMT613 base alloy,its YS increases from 333MPa to 352 MPa,UTS increases from 373 MPa to 418 MPa,and the elongation rate is increased from 2.6% to 4.3%.