Study On The Microstructure And Properties Of Heat Resistant Magnesium Alloys Mg-10Gd-3Y-xNd-0.5Zr

Mg-RE alloys possess good mechanical properties under normal and high temperature especially the creep resistance,leading them widely used in the automotive and aerospace industries.In recent years,although the research on heat-resistant magnesium alloys such as Mg-Gd-Y-Zr increase day by day,its mechanical properties still have the potential for further improvement.In this paper,by adding different contents of Nd with the weight percentage of 1%,2%,3%,4% into Mg-10Gd-3Y-0.5Zr alloy,the effect of Nd on the microstructure and mechanical properties are studied.The results show that the microstructure of as-cast Mg-10Gd-3Y-0.5Zr alloy is composed of ?-Mg matrix and Mg5(Gd,Y)phase,and a new phase Mg41Nd5 can be found after the adding of Nd.It is concluded that the proper addition of Nd can improve the microstructure and strength of the alloy.When the addition of Nd is up to 2%,the tensile strength,yield strength and elongation of Mg-10Gd-3Y-0.5Zr alloy are 216 MPa,209MPa and 2.6%,respectively.After solid solution treatment with holding 6 hours at the 535?,most of the phases at the grain boundaries of the as-cast Mg-10Gd-3Y-2Nd-0.5Zr alloy dissolve in matrix.Then the alloy is aged at 225 ? with different time.With the increase of aging time,the Brinell hardness values for the alloy increase first and then decrease,and reach to the maximum value when the aging time is 14 hours.So the best heat treatment process can be identified as solid solution 535 ? × 6h and aging 225 ? × 14 h.With the increase of Nd content,the mechanical properties of aged Mg-10Gd-3YxNd-0.5Zr alloy at low temperature(room temperature ~ 200?)decreased slightly,but the mechanical properties of the alloy at high temperature(250 ~ 350?)improved.With the increase addition of Nd,the heat resistance of the alloy increased graduall y.For the same alloy,with the increase of the experimental temperature,the tensile strength and yield strength increased first and then decreased,the anomalous temperature dependence phenomenon of strength appears.The elongation of the alloy decreases with the increase of Nd content,and the elongation increases with the increase of the experimental temperature.The main strengthening phase of aged Mg-10Gd-3Y-x Nd-0.5Zr alloys is ?" phase,?' phase and long period ordered structure(LPSO)phase with 18 R phase structure.Aged Mg-10Gd-3Y-xNd-0.5Zr alloys have excellent mechanical properties at room and high temperature.The tensile strength of the Mg-10Gd-3Y-2Nd-0.5Zr alloy maintains at 280 MPa or more in the range of 200 to 300?.And the tensile strength of the alloy is 309.5 MPa at 250?.When the experimental temperature is 350?,the alloy also shows excellent high temperature properties,and the tensile strength of the alloy is still up to 195 MPa,which is much higher than the commercial heat-resistant magnesium alloy WE54.The aged Mg-10Gd-3Y-2Nd-0.5Zr alloy has excellent creep resistance at(200 ?,250 ?,300 ?)/(50MPa,70 MPa,90MPa),which is obviously superior than that of commercial heat-resistant magnesium alloy WE54.When the creep temperature is 250 ?,the ?' phase turns into ? phase.And the ? phase grows obviously when the creep temperature is up to 300 ?.With the increase of the creep temperature and stress,the creep control mechanism changes from the diffusion and grain boundary sliding mechanism to dislocation slip and dislocation climbing mechanism.