On the nature of solutal and contact melting in Cu-Pd and Al-Cu

Kurzfassung

Melting plays an important role in many technical processes such as casting, additive manufacturing, brazing, welding, soldering etc. but is far less understood than solidification. Contributing to a better understanding of the melting process, we investigated solutal melting in Cu-Pd and Al-Cu and contact melting of Al-Cu. The isothermally processed samples were in-situ investigated employing X-radiography. By varying sample thickness, we observed a strong influence of buoyancy-driven convection on solutal melting. Persistent non-equilibrium conditions were found for the solid-liquid interface at the end of melting in all conditions. Asymmetric reaction patterns were observed to arise due to Al2O3-layer build-up and/or initial Al2O3-presence at the Al-Cu interface and/or partial Al-detachment. We observed contact melting to be initiated along Cu-grain boundaries with intermetallic layers representing the entire phase diagram forming between the liquid and the still solid copper. The layer structure has been verified post-mortem by optical imaging and quantified by SEM-EDX.