Susceptibility of Mg–REM–Zn–Zr Magnesium Alloys to Casting Unsoundness

The production of various housings of the units operating under the pressure of liquids or gases requires the use of alloys with increased soundness after casting. We compare the properties of the magnesium alloys most widely used for producing leakproof castings, namely, ML10, Elektron 21, EZ33A, ZE41A, and ZE63A. For each of them, the equilibrium and nonequilibrium freezing ranges, the heat of solidification, and the fraction of eutectic in a structure are calculated, and the dynamics of the change in the rate of solidification of an alloy in the freezing range is estimated. The shape and size of shrinkage cavity in castings made of the alloys are also determined, and the shrinkage porosity of the castings was measured. The causes for the low soundness of the ML10 alloy castings are considered. The contribution of the eutectic phase content and the freezing range wideness of an alloy to the formation of a soundness casting wall is shown to be decisive. The precipitation of a sufficient amount of eutectic in the cast structure of a magnesium alloy ensures high soundness even in the presence of shrinkage porosity in a casting. The best tightness among the alloys is demonstrated by the EZ33A and Elektron 21 alloys, which have a sufficient amount of eutectic and a short freezing range.