In Situ Analysis of Incipient Melting in a Novel High Strength Al–Cu Cast Alloy Using Laser Scanning Confocal Microscopy (LSCM)

Incipient melting in a novel Al–Cu alloy was investigated. Overheating during heat treatment leads to incipient melting thereby compromising mechanical properties. Advanced microscopy and real-time imaging techniques such as high-temperature LSCM enable a direct in situ observation of incipient melting and phase transformations. Hence, isothermal analysis was carried out using LSCM at elevated temperatures to analyze incipient melting with time. The predominant phase of this alloy was Al₂Cu in both blocky and eutectic morphologies. The results showed that incipient melting was accompanied by a clustering of liquid droplets followed by a complete melting of Al₂Cu at approximately 548 ℃. The in situ analysis also revealed that eutectic Al–Al₂Cu was found to melt prior to blocky Al₂Cu. Further, localized melting was also observed to occur at a random sequence. As a result of incipient melting, the microstructure consisted of a proliferation of defects such as brittle ultra-fine eutectic clusters and porosity.