Globular structure generation and mechanical properties of thixoformed magnesium alloy

For the alloy to be shaped in the semisolid state, it must have an appreciable melting range; before thixoforming, the microstructures must consist of solid metal spheroids in a liquid matrix. Equal channel angular extrusion (ECAE) was used as a process to predeform as cast AZ80 magnesium alloy before partial remelting. The results show that fine and equiaxed grains are obtained due to dynamic recrystallisation during ECAE. Following partial remelting in each case, the microstructure consisted of globular solid grains with liquid film along the grain boundaries. During partial remelting, solid grain sizes at 560°C were smaller than those at 550°C. Moreover, the degree of spheroidisation at 560°C was greater than that at 550°C. Good mechanical properties are obtained for the thixoformed AZ80 alloy prepared by six-pass ECAE with a yield strength of 210 MPa, an ultimate tensile strength of 320 MPa and an elongation to fracture of 9·2%. The results also show that the process, ECAE plus partial remelting, can ...