Evolution Of Microstructure And Texture During Recrystallization Process In Rolled Wrought Mgal Based Alloys

Magnesium alloys are the third metallic structural materials which developed after steels and aluminum alloys. As their high specific strength and specific rigidity, they have been used in the fields of automobile, aerospace and aviation and3C (Computer, Communication and Consumer Electronics) products. At present, the magnesium alloys which have been applied widely is cast magnesium alloys, although wrought magnesium alloys have better performance. The magnesium alloys which crystal structure is hexagonal close-packed type have less slip systems, and poor plasticity near the room temperature, so wrought magnesium alloys are usually processed and manufactured at high temperature. This measure will increase the cost of producing wrought magnesium alloys to a certain degree. Moreover, high temperature plastic deformation usually gives rise to a strong basal texture in wrought magnesium alloys, therefore how to improve the room temperature plasticity of magnesium alloys is one of important research areas of magnesium alloys. As it’s known to all, recrystallization texture is an important microstructure characteristic which forms with recrystallization process. The mechanism of recrystallization texture has no reasonable explanation at present. So expound the mechanism of recrystallization texture will play a key role in understanding the recrystallization process of magnesium alloys roundly and truly.Based on the above idea, research works were focused on following aspects:(1) Structure of magnesium alloys dynamic recrystallization physical model;(2) Dynamic recrystallization microstructure and texture evolution of hot-rolled AM31sheets;(3) Static recrystallization microstructure and texture evolution of cold-rolled and annealed AZ31sheets.As the grains in as-cast magnesium alloys have random orientation, the grains can be classified into three categories according their orientation during rolling process:basal plane grain that is difficult to slip on basal plane and form tension twin;45°grain that is easy to slip on basal plane;90°grain that is easy to form tension twin. These three kinds of grains have different behavior in recrystallization process. The basal plane grain will "remain" through high temperature plastic deformation because of its feature that easy to form and difficult to disappear. This paper took the fact above as a starting point, and raised the dynamic recrystallization texture mechanism of magnesium alloys——Basal Plane Grain "Remain" Mechanism.Dynamic recrystallization, accompanying grain refinement and formation of basal texture, occurred during hot rolling of as-cast AM31sheets at350℃. With the increasing of reduction, grains were refined gradually, grain size was more and more homogeneous, the amount of twins was reduced, and the intensity of the basal texture increased. The dynamic recrystallization microstructure and texture evolution during this process can be well explained by Basal Plane Grain "Remain" Mechanism.Recrystallization occurred during cold rolling and300℃annealing of extruded AZ31sheets which have strong basal texture. After the first pass cold rolling and annealing, the grains were refined, the intensity of the basal texture reduced greatly at the same time. However, in subsequent cold rolling and annealing, grain size showed a trend of first increasing and then decreasing, while the intensity of the basal texture increased step by step. The recrystallization microstructure and texture evolution during this process also can be well explained by Basal Plane Grain "Remain" Mechanism. While annealing process, recrystallization prefers to nucleate near shear band. After the first pass cold rolling and annealing, the yield strength of AZ31decreased while the elongation increased.