Study On Indirect Extrusion Process And Heat Treatment Of Magnesium Alloy

Magnesium alloy, as the lightest structure materials, has been widely used in military, aerospace, automobile and electronic communication industries due to its advantages of high specific strength, high stiffness, good damping capacity and electromagnetic shielding. Plastic deformation can effectively improve the mechanical properties of cast magnesium alloy, while wrought magnesium alloy has higher strength and ductility than those of cast magnesium alloy. In this paper, whole lubricant indirect extrusion and whole lubricant hollow billet indirect extrusion, respectively, were used to produce rods and tubes of AZ31, ZK60, AM60and Mg-Gd-Y-Nd-Zr alloys. Heat treatment after extrusion was also studied. The conclusions are listed as follows:(1) When Sn (≤1%) is added into AZ31, ZK60and AM60alloys respectively, no precipitation can be observed, Sn exists in a solution state. Sn can refin the as-cast and extruded structures in those three alloys. Low Sn (0.5%) alloy has the best refining effect. When adding0.5%Sn into these three alloys, there tensile strengths and yield strengths increase oberviously, but elongations change little. However, both tensile strength and elongation decrease significantly by adding1%Sn into these three alloys.(2) When extrusion temperature decreases from380℃to350℃, grains of Mg-7Gd-3Y-1Nd-0.6Zr rods and Mg-3Gd-7Y-1Nd-0.6Zr alloys become finer, strengths increase, and elongations vary little. At the same extrusion temperature, strengths of these two different alloys are identical, but the elongation of Mg-7Gd-3Y-lNd-0.6Zr alloy is larger.(3) The optimum heat treatment method of Mg-7Gd-3Y-lNd-0.6Zr and Mg-3Gd-7Y-lNd-0.6Zr rods is aging treatment directly,200℃×68h. After T5treatment, maximum tensile strength, the yield strength and elongation of Mg-7Gd-3Y-1Nd-0.6Zr and Mg-3Gd-7Y-1Nd-0.6Zr alloy rods are391.8MPa,350.9MPa,5%,433.2MPa,356.4MPa and1.3%respectively.(4) With the increase of extrusion ratio, Refining effect of AZ31and ZK60tubes increases obviously. Strength increases, while elongation decreases. With the increase of extrusion temperature, grains grow, both strength and elongation decrease. The maximum tensile strength and yield strength of AZ31tubes could reach325.6MPa and210.2MPa respectively, while elongation is10%.The maximum elongation value of AZ31tubes could reach15.1%. The maximum tensile strength and yield strength of ZK60tubes could reach362.1MPa and274MPa respectively, while elongation is9.7%. When extrusion temperature is350℃and extrusion ratio is12, elongation of ZK60tubes can reach maximum value17.8%.(5) The optimum heat treatment method of ZK60tubes with a large extrusion ratio is T5treatment. Grains get finer after T5treatment, and tensile strength and yield strength of alloys reach the maximum value, while elongation has no large change.