No abstract

Grain refinement is known to be an effective method to improve the poor ductility at room temperature, as well as to achieve an excellent formability caused by superplasticity at high temperatures, in magnesium alloys. In the present study, as an attempt to develop a convenient grain refinement method, wrought products of a commercial magnesium alloy AZ31 have been subjected to further cold rolling and subsequent annealing. The influence of the angle between the original working direction and the cold rolling direction on the grain size has also been investigated. A hot rolled sheet and an extruded bar were cold rolled by 15 directly and after annealing at 250°C for 1 h, respectively, subsequently annealed at 250°C for 1 h, and then subjected to optical microscopy. The present process consisting of cold rolling and subsequent annealing was found to be effective to refine the grain size. Grain refinement became more marked when the angle between the original working direction and the cold rolling direction increased. Yield strength and hardness were confirmed to increase with decreasing grain size. The minimum grain size obtained in the present study was 6.4 mm, which seemed to be sufficiently fine for the occurrence of superplasticity.

The hot-rolled and extruded AZ31 specimens are subjected to tensile tests at room and elevated temperatures. At room temperature, the yield stress of the hot-rolled specimen is significantly higher than that of the extruded, the reason for which is related to the different textures developed in the two type specimens, as well as the different slip systems activated. At elevated temperatures, the strain rate sensitivity and the activation energy are obtained to characterize the deformation mechanism of the alloy during the temperature range of 423~573K.

No abstract

A convenient grain refinement method has been developed in wrought magnesium alloys. Commercial hot-rolled sheet and extruded bar of AZ31 alloys were subjected to further cold rolling and subsequent annealing. The influence of the angle, , between the original working direction and the cold-rolling direction on the grain size was also investigated. The present process was found to be effective to refine the grain size. Grain refinement became more marked when increased. Yield strength and hardness were confirmed to increase with decreasing grain size.