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实用铝合金铸件的缩松具有与其合金组分不同的性质。因此,为了生产无任何缺陷的致密铸件,必须创造使合金液的补缩能填补铸件收缩的铸造条件。我们研究了Al-Si合金铸件的凝固过程,并随之测定了为了生产无任何缩松缺陷的铸件要求合金液朝向冒口凝固的位置(由此得到能消除任何这类缺陷的补缩极限固体比和合金硅含量对它的影响)。含7%Si的Al-Si合金的补缩极限固体比约为0.41。意思是如果在固体比达到0.41以前合金进行定向凝固不产生缩松缺陷。固体比达到或超过0.41的定向凝固产生缩松缺陷。含4～10%Si的Al-Si合金的补缩极限固体比随合金硅含量增多而变低。换言之,含硅量较高的合金在凝固的初期阶段补缩不太流畅。因此,为了生产无缩松缺陷的致密Al-Si合金铸件,随着合金含硅量的增加,即使在凝固的初期阶段,在更大程度上促进定向凝固是十分必要的。于是,如果能确定Al-Si合金铸件在达到补缩极限固体比之前是否进行定向凝固,就可以知道它是否存在缩松缺陷。换言之,从以补缩极限固体比为基础的凝固状态图上的凝固前沿的形状,可以预测任何缩松缺陷的产生。
The shrinkage of practical aluminum alloy castings has different properties from its alloy components. Therefore, in order to produce dense castings without any defects, it is necessary to create casting conditions that allow the alloy fluid to fill and shrink the castings. We investigated the solidification process of Al-Si alloy castings and subsequently determined that in order to produce castings without any shrinkage defects, the alloy liquid is required to solidify toward the riser (thereby yielding a shrinkage limit solid that will eliminate any such defects Than the silicon content of the alloy and its impact). The AlSi alloy with 7% Si has a Slim ratio of about 0.41. This means that if the alloy was subjected to directional solidification before the solid ratio reached 0.41, no shrinkage defects were produced. Directional solidification at or above 0.41 solidification results in shrinkage defects. The limiting solid limit of the Al-Si alloy containing 4% to 10% Si decreases with the increase of the alloy Si content. In other words, higher silicon content of the alloy in the early stages of solidification shrinkage is not smooth. Therefore, in order to produce dense Al-Si alloy castings without shrinkage defects, it is necessary to promote the directional solidification to a greater extent even with the increase of silicon content in the alloy even in the initial stage of solidification. Thus, if it is possible to determine whether Al-Si alloy castings have been set to directional solidification before reaching the Slim ratio, it is possible to know whether there is a shrinkage defect. In other words, from the shape of the solidification front on the solidification state diagram based on the limit-of-solid-solid ratio, it is possible to predict the occurrence of any shrinkage defect.