Abstract
Plastic formability in the secondary processing of an AZ31 magnesium alloy was investigated using fine-grained and relatively coarse-grained materials, respectively. To produce components for mobile electric appliances, boss formability was examined at a relatively low temperature of 523 K. The boss with a height of 14 mm was successfully formed in fine-grained material under a nominal forming pressure of 582 MPa in 5 s. Analysis of the boss forming revealed that the forming occurred under the high-strain-rate superplastic condition. The grain size in the boss region was slightly coarsened, probably as a result of strain-induced grain growth, which is a widespread property of superplastic flow. On the other hand, even in the coarse-grained material, a relatively high boss height of 5 mm was obtained under the same forming condition. After the boss forming, grain refinement was observed in the coarse-grained material. It was suggested that the coarse-grained materials exhibited relatively high formability because of dynamic recrystallization. It was concluded that plastic forming concomitant with grain growth was more effective than that concomitant with grain refinement in AZ31 magnesium alloy. An empirical equation to perform plastic forming under the condition concomitant with grain growth was developed.
