On the Dimension Contraction of Low-Pressure Sand Cast Mg-Gd-Y-Zr Alloy.

The unclear contraction behavior of Mg-Gd-Y-Zr alloy during low-pressure sand casting bring obstructs into the dimensional control in the fabrication of large and complex parts, restricting the further engineering applications of this alloy. This paper investigated the rule for free and constrained contraction of typical Mg-Gd-Y-Zr (Mg-9Gd-3Y-0.5Zr, VW93K) alloy during low-pressure sand casting. A series of castings with different volumes and geometric structures were designed and a 3D scanner was employed to measure different types of dimensions, which were then used for the calculation of contraction coefficients. The convergent value of free contraction coefficients was derived through statistical analysis, and the correlation between constrained contraction coefficients and geometric characteristics of castings was established by the utilizing of core volume factor. In the condition of low-pressure casting, free contraction coefficients of VW93 alloy are concentrated around a fixed value of 1.72%, constrained contraction coefficients of VW93 alloy show a decreasing linear tendency against core volume factor, and pouring pressure makes effects on free contraction. The experimental results and proposed formulas provide guidance for accurate dimensional control in fabrication of large and complex Mg-RE alloy parts by low-pressure sand casting. [ABSTRACT FROM AUTHOR]