Microstructure control and formability of AZ31 alloy processed by different-speeds-rolling

The effect of different-speeds-rolling (DSR) processing on microstructure, mechanical properties and formability of AZ31 alloy was investigated. The speed ratio of the upper roll and lower one was selected to be 1.364, while the rolls temperature was controlled from ambient temperature to 573K. The preheating temperature of the billet sample was varied from 573K to 673K, depending on the roll temperature, in order to gain AZ31 sheets free of cracks with final thickness of 1.0 mm. The influences of rolling conditions and post heat treatment on microstructure, mechanical properties and formability of the rolled AZ31 sheets were examined by several techniques such as optical microscopy, hardness tests, tensile tests and conical cup tests, either at ambient or at elevated temperature. It is found that the DSR processing has a remarkable grain refinement effect to produce grain sizes of 10-20 mu m for the investigated Mg alloys, and the rolled sheets exhibit remarkably strong texture and anisotropy in mechanical properties under the testing conditions. This work is a preliminary attempt and detailed investigations are in progress for generating more scientific knowledge of the DSR technique and also for manufacturing high performance Mg alloy sheets.