Repeated Unidirectional Bending And Its Effect On Texture And Properties Of AZ31B Magnesium Alloy Sheet

Magnesium alloys, the lightest constructional metallic material with high strength, good thermal conductivity and the characteristics of the shock absorber, are considered as 21 century's green materials. However, the applications of magnesium alloys, specially wrought magnesium alloy, are still limited due to their poor formability. Most magnesium alloys were manufactured into electronic product shells by die casting, such as cameras, cell phones and laptops. If these shell products were made by stamping using magnesium alloy sheet, it can not only make full use of excellent mechanical properties of magnesium alloy, but also substantially improve production efficiency and qualification. Thus, research on formability and process of magnesium alloy sheet is the key to expand the application.Presently, research of magnesium alloy stamping process has got some achievement, but report on how to improve formability of magnesium alloy is rare. Cold rolled magnesium alloy sheet has strong (0002) textural component, less slip systems and strong anisotropy at room temperature which are harmful to formability. In this paper, a new method, repeated unidirectional bending (RUB) was used to improve the textural components of cold rolled magnesium alloy sheet in order to obtain better formability.Focused on development of formability of magnesium alloy sheet, the technological parameters were determined by orthogonal experiment using a homemade RUB equiqment so that optimal RUB method was acquired. Cold rolled AZ31B magnesium alloy sheet was bended using the optimal method mentioned above. By analyzing microstructures, mechanical properties, Erichsen value and textural components of the samples, it was found that grains had rotated after RUB which demonstrated textural components evolution. The strong (0001) textural component which was harmful to post forming had been greatly weakened. And there was no obvious change on microstructure. Lots of ( 1 2 1 2),( 1 2 1 1)and (01 1 0)and a few(01 1 2),(01 1 1)textural components appeared.When annealed at 135℃for an hour, massive annealing twins apperared and(01 1 2)(,01 1 1)components increased. The textural components presented complex and diverse. When annealed at 260℃for an hour, grains near to sheet surface grew up through static recrystallization. Here main textural components were( 1 2 1 2),( 1 2 1 1),(01 1 2),(01 1 1). Grain orientation of corresponding texture focused because of nucleation and directional core growth. Schmid value of basal plane increased when sheet was under tension or compression deformation. Therefore, basal slip system became easier to start. Owing to the change of textural components, strength and yield ratio of the sheet reduced and elongation increased to 38% at most. Anisotropy of the sheet became more obvious after RUB while Erichsen value dramaticly increased to 67% at most. As we can see, RUB can well improve formability of cold rolled AZ31B magnesium alloy sheet.Moreover, in this paper, intermediate and high temperature RUB process was also researched preliminarily. Result indicated that (0001) textural component was still weakened, but grains coarsened due to dynamic recrystallization during deformation. Grain size became the chief factor of formability. Thus, the development of magnesium alloy sheet formability of intermediate and high temperature RUB was limited. The RUB process at normal temperature is the better.