Formation mechanisms and prediction of solidification defects in aluminum alloy castings

Porosity and hot tearing are representative defects in solidification of shape castings. They are all related to lacking of feeding at the final stage of solidification but have different forming mechanisms. The hydrogen has high solubility in melt of aluminum alloy but will be released during solidification. The supersaturation pressure of the gas and pressure drop induced by solidification shrinkage all contribute to the formation of porosity. Hot tearing usually occurs due to blocking of shrinkage and lacking of feeding, and is related to alloys properties, casting technology in the shaping of castings. Based on the fundamental researches of solidification, formation mechanisms and several classical prediction criterions of these two types of solidification defects were generalized. Analyses and discussion were done for the formation criterion and key parameters. Finally the research directions of new criterion and the problems to be resolved immediately were given.