Effect Of Ag On Microstructure And Mechanical Properties Of Mg-2.5Nd-1.0Sm-0.4Zn-0.1Ca-0.5Zr Alloys

To develop a magnesium rare earth alloy with both high strength and high plas-ticity to meet the urgent need for the development of new aero-engine component materials,this article uses Ag alloying,hot extrusion and heat treatment to improve the microstructure and mechanical properties of Mg-Nd-Sm-Zn-Ca-Zr alloys.The effect of Ag content on the microstructure and mechanical properties of the as-cast,aging,hot extrusion and subsequent aging states of the alloy was studied.By adjusting the Ag content,the as-cast Mg-2.5Nd-1.0Sm-0.4Zn-0.1Ca-0.5Zr-x Ag(x=0,0.5,1.0,1.5 and 2.0)alloy was prepared.The addition of Ag promotes the formation of the?phase(Mg Ag)₁₂(Nd Sm Zn),reduces the formation enthalpy,shear modulus,Young's modulus and elastic anisotropy of the?phase,and improves the bulk modulus and toughness of the?phase.The strength of the as-cast alloy gradual-ly increases with increasing Ag content,and the elongation gradually decreases.When the Ag content was 2.0 wt.%,the tensile strength of the alloy was 196 MPa.After solid solution and aging treatment of the as-cast alloy,lamellar??phases pre-cipitated along the?-Mg prism surface in the alloy without Ag,and the length was10 nm to 20 nm.The addition of Ag promoted the formation of the basal???phase.With increasing Ag,the tensile strength of the aged alloy first increases and then de-creases,the yield strength gradually increases,and the elongation gradually decreas-es.When the Ag content is 0.5 wt.%,the tensile strength of the aged alloy is the highest(258.1 MPa).In addition,as the aging time increases,the size of the precipi-tates in the 0.5 wt.%Ag alloy gradually increases,and the number first increases and then decreases.During the peak aging period(9 h),the number of???and??phases is the largest,with lengths of 10 nm to 20 nm.During the overaging period(200 h),the coarse and lamellar?₁ phases are dominant,with lengths of 200 nm to 500 nm.After the Mg-2.5Nd-1.0Sm-0.4Zn-0.1Ca-0.5Zr-x Ag(x=0,0.5,1.0,1.5 and 2.0)alloy was hot-extruded at 400°C,with the addition of Ag,the grains gradually be-came finer.The intensity gradually increases.When the Ag content was 2.0 wt.%,the grain size was 6.9?m.Compared with the alloy without Ag,it is refined by27.36%,and its tensile strength,yield strength and elongation are 250.5 MPa and170.1 MPa,respectively.In addition,17.8%.After the aging treatment of the hot-extruded alloy,the amount of??and???in the Ag-free alloy is less,and the length is less than 30 nm.When the Ag content increases to 2.0 wt.%,the number of??and???phases increases significantly,and the alloy has both good strength and plasticity.Its tensile strength,yield strength and elongation are 288.2 MPa,198.7 MPa and 12.6%,respectively.