| Traditional Mg-Nd-Zn-Zr alloys have poor microstructure stability、toughness and low bearing strength.In order to improve the strength and plasticity of Mg-Nd-Zn-Zr alloy,the solution treatment and extrusion aging process was studied.In this paper,the alloys were treated at 530℃ for 1.5-24 hours.To found the optimal solution time,the internal structure of the alloys at different solution treatment was observed by optical microscopy and scanning electron microscopy.After the extrusion process,aging treatment was carried out uniformly,and analysis the effect of intermetallic compounds on properties of alloys.In the state of the optimal solution treatment,the extrusion deformation experiment was carried out at the extrusion temperature of 250-400℃ and the extrusion ratio of 10.5 and 16 respectively.The mechanical properties of the alloys were tested.The effect of extrusion process on the texture and properties was analyzed by EBSD and TEM.The engineering application experiment is also carried out.The results show that the Mg-Nd-Zn-Zr alloy is composed of α-Mg and Mg12 Nd in as-cast state.After solution treatment at 530℃ for 9 hours,the eutectic at the grain boundary of the alloy basically solves completely.There are Zr segregation zones in the alloy after solution treatment.At 24 hours of solution treatment,there will be α-Nd segregation zone,and the grain grows to about 60 μm.After 9 hours of solution treatment,the strength of the alloy is higher during extrusion at 300℃,the yield strength is 170 MPa,and the tensile strength is about 240 MPa.After extrusion,the grain size is about 4 μm and the elongation reaches 40%.The grain growth in the alloy after 24 hours of solution treatment results in the worse properties of the alloy after deformation.After extrusion,the texture of the alloy is weak and the strength is about 2.7,the grains are in the position of soft orientation,and have larger Schmid,which is easy to slip and has higher plasticity.The strength of the alloy increases by 20 MPa and the elongation decreases after aging treatment at 200℃for 9 hours.After extrusion at the extrusion ratio and temperature of 10.5 and 250℃,the yield strength and tensile strength of the alloy are 240 MPa and 280 MPa,respectively,and the elongation reaches 30%.After extrusion at the extrusion ratio of 16,The plasticity of the alloy reaches 40%,the yield strength and the tensile strength are about 180 and 250 MPa,respectively.TEM results show that there are many fine precipitates in the alloy after extrusion at the extrusion ratio of 10.5,which is identified as Mg12 Nd.Block Mg-Nd precipitates and linear Mg-Zn phases are found in the alloy after extrusion at the extrusion ratio of 16.In addition,the grain boundary of the alloy is more obvious and the recrystallization is more complete than that of the alloy after extrusion ratio of 10.5,at the same time,the grains in the alloy are mostly in the position of soft orientation,which makes the plasticity of the alloy better.After extrusion at the extrusion ratio of 10.5,there has a locally concentrated plastic deformation zone in the alloy.Moreover,There are so many precipitates in the alloy that pins the movement of dislocations and improves the strength of the alloy.At the same time,the hard-oriented grains account for a large proportion and the plasticity is poor.It is found that the hardness value of the alloy after extrusion at the extrusion ratio of 10.5/16 reaches the maximum after aging treatment at 200℃ for 9hours,which is about 77 and 67 HV,respectively.The high toughness of the extruded alloy is mainly attributed to the precipitation of the second phase in the alloy and the fine grain structure in the soft orientation position.With the increase of extrusion temperature,the grains in the alloy will grow and the toughness will decrease.The plasticity of Mg-Nd-Zn-Zr alloy backward extrusion barrel for industrial application increases while its strength decreases after the second solution treatment at 530℃ for 9 hours,and the yield strength and tensile strength increases by 40、50 MPa respectively after aging at 200℃ for 14 hours. |
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