Optimum hot forming temperature of AZ61 magnesium alloy

A new concept of stability of materials is introduced by defining the optimum hot forming temperature for any given strain rate. This temperature is obtained through forming maps that are based on Lyapunov concepts and the introduction of a Garofalo equation in the Lyapunov criterion. This new approach is applied to a magnesium alloy AZ61. Torsion tests were carried out in the temperature range 574–734?K and strain rate range 0.7–8.7?s^?1 and the microstructures were determined using optical microscopy. Using the peak stress, optimum workability at 630?K is obtained at 12?s^?1. The results and the maps are compared with data and maps of other authors for AZ61 alloys in various states.