The Recrystallization Behavior Of Magnesium Alloy AZ31 By Rolling

Magnesium alloys have been paid a great deal of attentions in recent years. However, magnesium alloy possesses poor formability at room temperature because of its hexagonal closed packed (HCP) crystal structure. Grain refinement is known to be an effective method to improve the poor mechanical properties. The most practical technique of grain refinement for magnesium alloys is dynamic recrystallization and rolling combined with suitable heat treatment.The microstructure and mechanical properties of rolled magnesium alloy AZ31 were studied at different rolling reductions and temperatures. The results show that the grain size is a function of strain, strain rate and temperature. With the increasing of rolling reduction and temperature, nucleus amount of dynamic recrystallization is increased, more grains are refined. However grain size becomes coarser as rolling reduction and temperature is too high. The intensity of {0002} basal component increases with increasing reduction and decreases with increasing strain rate. Under the same deformation condition, the grain size of magnesium alloy sheet rolled by cross shear rolling is finer than normal rolling. Besides, the intensity of {0002} basal component was weakened, the tensile strengths decrease and the tensile elongation increases.The microstructure and mechanical properties of rolled magnesium alloy AZ31 were investigated upon annealing under different conditions. The results show that twinning takes place in all the grains in AZ31 magnesium alloy rolled at 300℃. The twins disappeared gradually and recrystallized grains formed after annealing. Grain size grows larger as the annealing temperature is elevated and reduces at first then grows as the annealing time is prolonged. In addition, the tensile strengths of annealed alloy descend slightly, while tensile elongation increases. The highest elongation is 28% after annealed at 200℃ for 120min. Normal grain growth takes place upon annealing. Grains with {0002} basal planes parallel to the sheet plane grow at the expense of grains with other orientations. The intensity of {0002} basal component increases with the increasing annealing temperature and prolong times.