Assessment of Eutectic Modification Level in Al-Si Alloys Via Thermal Analysis

The modification level (ML) of A356, A319, and A413 Al-Si alloys was investigated via thermal analysis (TA) and microstructural investigation. The modification treatment was carried out using different levels of Sr in the form of Al-10 wt% Sr master alloy. The melt was poured into three different types of molds to give different cooling rates (CRs) to simulate the actual casting conditions. Increasing the level of Sr improved the ML of the eutectic Si. Slower CRs required higher additions of Sr to produce the same ML obtained from the higher CRs. An attempt was made to assess the ML at the high CRs with the aid of the TA parameters measured at the slow CR. Thermal analysis was found to provide successful quantitative measure for the modification level in A356. In A319 and A413, thermal analysis could provide successful quantitative measure of ML when the ML was below 4.0. It could provide only qualitative indication of the occurrence of modification when the ML was 4-6. The latter findings were found independent of cooling rate.