Microstructure Evolution of Cast Mg AZ31B Alloy at Low Superheat

It is well known that casting at low superheat has a strong influence on the solidification morphology and macrostructures and microstructures of the cast alloy. This paper shows the microstructure of cast Mg AZ31B alloy at superheat of 5C (41F) and describes a stochastic mesoscopic solidification model for predicting the grain structure of the cast alloy. Casting experiments were carried out using the Magnetic Suspension Melting (MSM) process, which is an integrated containerless induction melting and casting process. Casting at this low superheat was found to produce castings with a fine globular grain structure with an average grain size of about 80 μm, which is much smaller than that obtained by conventional casting techniques. The stochastic model was found to reasonably predict the observed grain structure. This makes the model a useful tool for controlling the structure of cast magnesium alloys.