Dissolution of Eutectic β-Mg_(17)Al_(12) Phase in Magnesium AZ91 Cast Alloy at Temperatures Close to Eutectic Temperature

摘要

Knowledge on the dissolution kinetics of β_(-eut) phase in cast Mg AZ91 alloy at temperatures close to the eutectic temperature is very useful for various processes of the alloy. In the present study, dissolution of β_(-eut) phase has been investigated experimentally and considered theoretically. Results have confirmed that the kinetics of β_(-eut) dissolution is basically diffusion controlled. Optimum times for dissolution heat treatment practice of different sizes of cast microstructure which are cooling rate dependant during casting could be suggested based on the present calculation. For fusion welding of the alloy, the present results indicate the difficulty of having a heating rate lower than the critical value ("critical heating rate") for a significant reduction of the phase to avoid constitutional liquation.