2013 Volume 85 Issue 5 Pages 262-267
Phosphorus impurity in hypo-eutectic Al-Si alloys has adverse effects on their mechanical properties, especially toughness. Moreover, it causes the shrinkage characteristics to become worse and the inverse segregation layer to become thicker. Modification treatment has been used in the past to avoid these effects. However, there are problems of over-modification of the duration of effectiveness and of the rapid increase of hydrogen. Hence, a de-phosphorization treatment using flux was tested on Al-7%Si alloy and AC4CH alloy. In addition, studies were conducted on the de-phosphorization mechanism and modification of the eutectic structure. The results were as follows. 1) It was found that the phosphorus content in the molten metal decreases with the addition of large amounts of flux and removal of the generated slag after vigorous stirring. 2) In this process, the eutectic structure is changed from un-modificated to modificated. 3) The dephosphorization mechanism is considered to be the oxidation of sodium phosphide, and its attachment and removal by the molten chloride.
