Microstructure Evolution And Mechanical Properties Of AZ80 Magnesium Alloy By Multi-directional Extrusion

Magnesium alloy has been widely used in modern industrial production, but mainly based on as-cast product whose mechanical behavior is relatively low. Multi-directional extrusion technology can effectively refine microstructure of magnesium alloy, and become a more effective means to improve the overall performance of magnesium alloy. In this paper, homogenization treatment was used in the as-cast AZ80 magnesium alloy to eliminate its defects, and different process parameters were carried out for the homogeneous AZ80 magnesium alloy. After these treatments, this paper studied the microstructure and mechanical properties of the AZ80 magnesium alloy, also analyzed the impact of the process parameters on microstructure and mechanical properties.Through the treatment of multi-directional extrusion under different time and strain for the homogeneous AZ80 magnesium alloy, the microstructure and mechanical properties of it were significantly improved. As time goes on, the tensile strength of the alloy showed a trend of first increase and then decrease. When the time is shorter and the degree of deformation is lower, the main mechanism of the grain refinement is twinning. With the upgrading of passes, dynamic recrystallization replace twinning and have a large number of members. At this time, the main mechanism of the grain refinement is continuous dynamic recrystallization. Continue to extend the time, the plastic ability of the alloy was greatly improved. However, due to the rapid growth of the grain, the tensile strength decreased significantly. By comparing multi-directional extrusion under different time, the best process parameter was extruded 3 passes in 15 minutes. In this situation, the grains were fine equiaxed which has the minimum size of 10μm and the maximum volume percentage of 75%. At the same time, the tensile strength, elongation and microhardness were 319MPa,7.25% and 76.Through the treatment of multi-directional extrusion with different temperature drop for the homogeneous AZ80 magnesium alloy, whose pass strain is 0.5 and 0.7, it had a more efficient grain refinement. In the premise of same pass strain, the effect of the extrusion for low temperature is better than that of high temperature. In the premise of same temperature, with the increase of deformation, the microstructure was greatly improved. Studies indicated that the best parameter was extruded 6 passes for 0.5 pass strain under 370 ℃. At the moment, the volume percentage reached 80% and the size of the grains was 3.5μm. Also the tensile strength, elongation and microhardness were 298MPa,6.78% and 80.At last, this paper discussed that the impact of different processes parameters on the microstructure and mechanical properties, such as pass strain, temperature and time. Pass strain becomes large so that the deformation becomes large, which provides energy to dynamic recrystallization for the grain refinement. With the extension of temperature and time, the size of the grains decrease and the mechanical properties increase. But when the time is too long and temperature is too high, it will lead to grain growth and mechanical properties decrease.