铝合金铸件中的凝固缺陷形成机理及预测

Formation Mechanisms and Prediction of Solidification Defects in Aluminum Alloy Castings

孔洞与热裂是铸件在凝固过程中最常遇到的典型缺陷。两者均形成于合金凝固末期,与液相补缩不足相关,但又有各自的形成机理。铝合金熔体对氢气有很大的溶解度,凝固过程中又因为溶解度的剧降而析出。孔洞是液相中过饱和的气体压力与凝固收缩引起的压力降共同作用的结果。热裂则是在凝固末期由于铸件收缩受阻而产生的应力以及液相补缩不足而导致的,其不仅与合金性质、铸造条件有关,并且受铸件形状的影响。文章基于近年来该方面的理论研究成果,总结了关于孔洞与热裂的形成机理以及几种目前所应用的经典预测模型,并对这几种模型的理论基础以及所考虑的关键参数进行了分析与讨论,在此基础上提出了未来新模型的研究方向和亟需解决的关键问题。

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 solubili- ty 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 bloc- king 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.