Determination of eutectic Si particle modification via a new thermal analysis interpretive method in 319 alloy

摘要

Knowledge of the Sr levels in Al-Si alloy melts gives an indication of the degree of Si modification possible. However, in the 319 alloy, Sr has been shown to react with alloying and impurity elements, reducing the quantity of Sr that can modify Si. Optical emission spectroscopy (OES) analysis, a quality control method used in foundries, can only indicate total Sr, both active and inactive, in the melt. Thus, thermal analysis has been used as a complementary tool to measure the Si modification level. The quantification of Si particle modification using thermal analysis has been studied and optimized during the last 20 years. The principle method of determining Si particle modification is to measure the suppression of the Al-Si eutectic growth temperature of the modified versus the unmodified alloy. This method is valid when Sr levels are low and the Al-Si eutectic growth temperature of the unmodified alloy is known. The authors wish to present new methods of fraction solid calculation and temperature-based parameters from cooling curves that have allowed more detailed interpretive methodologies to be utilized. These new methods allow more accurate and robust assessment of the AFS Si modification level via cooling curve analysis and do not require a reference temperature reflecting unmodified alloy solidification.