The Effect Of Extrusion Parameters On The Microstructures And Mechanical Properties Of Mg-6Zn-1Y-1Ce Alloy

The refinement of grain and second phase are the key factor for improvement of mechanical properties to magnesium alloys. In the present, the main methods to refine deformed magnesium alloys microstructures are by the means of several sever deformation technologies. RE process, as one of the sever deformation process can gives magnesium alloy high strengthen and ductility. The effects of reciprocating extrusion (RE) parameters, such as temperature, RE pass numbers and extrusion ratio, on microstructure, however, are not reported systematically. The author arms on above problems, therefore Mg-6Zn-1Y-1Ce alloy is selected. The microstructures are refined by using RE and extrusion (EX), respectively. RE processes are carried out at temperatures of 300℃,320℃,340℃and 360℃, with extrusion ratio of 7.72 (the diameters of die and container areΦ18mm and<Φ50mm, respectively) and 12.76 (the diameters of die and mould areΦ14mm andΦ50mm, respectively), and pass number from 1 to 6. EX processes are carried out at temperatures of 300℃,340℃,370℃and 400℃with extrusion ratio of 12.76, respectively. The microstructures are observed by OM, SEM and EDS, and the mechanical properties are obtained by tensile and hardness tests. The effects of extrusion ratio, temperatures, and extrusion pass number on the microstructures and mechanical properties are summarized; More details were given as follows.1) Reciprocating extrusion and direct extrusion both can refine the microstructures of CT-Mg-6Zn-1Y-1Ce magnesium alloys effectively, and microstructures are uniform, Matrix is refined by dynamic recrystallization (DRX). Temperature is the key factor to influence the dynamic recrystallization. While 340℃is the optimal temperature to extrude with parameters of 8MPa pressure,12.76 of extrusion ratio,1 pass, and the grain size was about 5μm. Extrusion pass is another important factor which is important to achieve fine grains. Reciprocating extrusion was taken on T4-Mg-6Zn-1Y-1Ce, that acquired 5μm finest grain after 4 passes extrusion, and the extrusion parameters were:300℃,8MPa, extrusion ratio of 7.72. 2) Compared with 1 pass, the structure of the CT-Mg-6Zn-1Y-1Ce ingot was coursing after 4 passes reciprocating extrusion at 8MPa pressure, extrusion ratio of 12.76, and temperature of 340℃. This indicates that the refine effect of 1 pass extrusion ia better than that of 4 passes. After microstructure analyzing it is found that the uniform secondary phase can pinning boundary in reciprocating extrusion after T4 thermal treatment. So the grain size was restricted in dynamic recrystallization.3) At 300℃, the CT-Mg-6Zn-1Y-1Ce alloy after direct extrusion has the finest grains. But over that temperature, dynamic recrystallization result in the increase of the grain size with the increase in temperature. The tensile strength is best after extrusion at 300℃, which was 317.43MPa; the elongation is best after extrusion at 340℃, which is 14.1%.