In-Situ Analysis of Incipient Melting and Characterization of a Novel Al-Cu Alloy for Cylinder Head Applications

Incipient melting of secondary phases during solution heat treatment of Al alloys is detrimental to their mechanical properties. In this research, incipient melting was analyzed in-situ using a high temperature Laser Scanning Confocal Microscope (LSCM) in a novel Al-Cu alloy. Thermal analysis and microstructural analysis were carried out on the alloy cast at fast and slow cooling rates to examine the resulting solidification and microstructural characteristics. The results showed that incipient melting was accompanied by a clustering liquid droplets followed by a complete melting of Al2Cu which occurred at approximately 548 ℃. Additionally, the use of LSCM enabled an understanding of the underlying mechanisms behind incipient melting. It was also found that incipient melting led to microstructure that consisted of a higher presence of ultra-fine eutectic clusters, needle-like Al2Cu and porosity along the grain boundaries. Lastly, the solution heat treatment temperature was optimized for the Al-Cu alloy using the data from LSCM, Differential Scanning Calorimetry and solution heat treatment experiments.