Influence of rolling direction on flow and cavitation in a superplastic magnesium alloy processed by equal-channel angular pressing

Experiments were conducted to investigate the influence of the rolling direction on the flow properties and the development of internal cavities in a magnesium AZ31 alloy. Billets were machined from the rolled alloy both parallel and perpendicular to the rolling direction and then processed by equal-channel angular pressing. Tensile specimens were cut from the billets after processing and pulled to failure over a range of strain rates at temperatures of 623 and 673 K. Superplastic elongations were achieved at strain rates of 10−4–10−3 s−1 with a measured strain rate sensitivity of ∼0.5. A quantitative examination of the internal cavities developed at 623 K showed that the smaller cavities grow by diffusion growth and the larger cavities grow by plasticity-controlled growth. The results show the flow properties and the cavity morphologies are essentially identical for specimens cut both parallel and perpendicular to the rolling direction. This similarity occurs because the cavities are nucleated at grain boundaries instead of at precipitates and therefore the rolling direction has no effect on either the flow or the cavitation behavior.