Study on the Thermal Contraction Behaviors of Mg and Al

Abstract

By using a device which could achieve the 1-Dimensional shrinkage instead of 3D shrinkage of the casting during the solidification and cooling, the cooling curves and the relationship between the shrinkage / temperature and time were investigated. Then, the thermal shrinkage behaviors of pure Mg and Al ingots were obtained. As a result, the characterization of the thermal shrinkage behavior of Mg and Al was systematically investigated. The results indicate that the contraction rate of pure Mg ingot increases with the increase of growth rate of dendrites in quantity during solidification. The maximum contraction rate νl, max will be reached when the formationof primary dendrite ends, and the value of νl, max is 1.12×10-2 mm·s-1. However, the shrinkage will not be present until the solid state cooling starting for the pure Al ingot. The contraction of pure Mg ingot in solid state can be divided into two stages: high temperature solid shrinkage stage and low temperature solid shrinkage stage. And the rate of shrinkage firstly increases then decreases with the temperature dropping at the stage of high temperature solid shrinkage. The rate of solid shrinkage of pure Al ingot is present at the beginning of solid-state cooling. And its value is 9.69×10-3 mm·s-1, which is more than 3 times of that of pure Mg ingot. The shrinkage behaviors of both pure Mg and Al ingots tend to be uniform shrinkage when the temperature is below 400°C.