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Abstract

Due to it's low density, Mg Al alloys are of high importance for modern lightweight structures and are widely used in automotive industry and consumer electronics. The properties of Mg Al alloys are primarily determined by their micro-structure consisting of two main phases where Mg-rich HCP-alpha-phase is enclosed by a near stoichiometric Mg₁₇Al₁₂ beta phase.

The morphology of Mg-Al alloys is set during casting and solidification. It is this step which controls the final corrosion properties of an alloy. Experiments reveal that the formation a closed shell of beta magnesium, preventing alpha-dendrites from building a network, is a good strategy to severely hinder the galvanic corrosion associated with the use of Mg-alloys in contact with more noble metals in automotive applications. In contrast, the low corrosion resistance of the Mg alloys found its application in medicine for the preparation of self degradable stents where it is essential to control the corrosion rate. Thus tailoring of the Mg Al alloy microstructure is of great importance utilizing and controlling its vastly varying corrosion resistance properties for a variety of applications.

We present simulations of the nucleation and equiaxed dendritic solidification of the primary Mg-HCP-alpha-phase followed by the nucleation and growth of a beta-phase in interdendritic regions. Several case studies will be presented where the effect of different processing and initial conditions is tested. These simulations help to better predict the properties of the final alloy based on the process parameters and increase understanding of the solidification process, which enables the design of Mg-Al alloys for different applications.