Effect of Ablation Casting on Microstructure of a Magnesium Alloy

Grain growth is a challenge in AZ magnesium alloys casting. The purpose of this research was to develop a finer microstructure than the conventional sand casting. In this study, a new method ablation casting was used. In the ablation casting method the mold must be washed after pouring and before the part complete solidification. In this way the part solidification rate increases. The sand mold was washed by water pressure 30 seconds after pouring in order to remove the heat content of the piece only by water. Thermal analysis was done by thermocouples that were placed in certain positions in mold. Then the cooling rates of samples were measured by them. The cooling rates in mushy zone were 1.27 and 0.52°C/sec for ablated and conventional casting parts respectively. The Cooling rate of the ablated part was 2.42 times further than the conventional CO2 sand casting. Size of dendrites decreased from 164.5 to 46.9µm with increasing cooling rate. During the solidification temperature gradients between two points of the ablated part was measured to predict of dendritic solidification. The temperature gradient mean between these points was 1.12°C/mm. In ablated sample, eutectic phase volume percent and precipitates were reduced. There was no change in shape of the pores in the ablated sample, but the volume percent of pores and maximum size was reduced. The average pore diameters were 82 and 42µm in ablated and control sample respectively.