The effect of ultrasonic treatment on the β-phase (Mg17Al12) morphology of an Mg-9.0wt.%Al alloy was studied. The result shows that with high-intensity ultrasonic vibration employed during the solidifying of Mg-9.0wt.%Al, the β-phase in the entire cross section of the billet is significantly refined and also changed from continuous to discontinuous morphology. Spherical β-phase is formed during the solidification of the billet treated with high-intensity ultrasonic vibration.
The deformation behaviour of a casting Mg-3.6%Er magnesium alloy after T6 treatment was studied in tensile tests from room temperature to 450 ℃ under different strain rates ranging from 1.0×10-4 to 6.0×10-3 s-1. Obtained local plateau in the temperature dependence of the ultimate strength (σ b) and yield strength (σ 0.2) under constant strain rate indicated the presence of dynamic strain ageing (DSA). Serrated flow was observed at the temperature of 200, 250, and 300 ℃. The observed negative strain rate sensitivity suggested that the serrated flow behavior arose from DSA. The temperature and strain rate dependence of the critical strain for the onset of serrated flow was analyzed using a phenomenological DSA equation, and the apparent activation energy Q for the serrated flow was obtained by calculation.
