Solidification behaviour in laser cladding of AlCoCrCuFeNi high-entropy alloy on magnesium substrates

The AlCoCrCuFeNi high-entropy alloy (HEA) was fabricated on pure magnesium substrates by means of laser cladding using a direct blown powder method. The coating can be categorised into two layers, a top AlCoCrCuFeNi HEA layer and a lower composite layer that consists of some partially melted HEA powders in an Mg based matrix. A metallurgically bonded interface was obtained between the Mg substrate and the HEA coating, with epitaxial crystals formed at the melting boundary of the substrate. In the solidification of the HEA alloy, some Cu was rejected into the Mg melt, however, no serious dilution of the HEA composition occurred in the top layer of the coating. The phenomenon of Cu rejection was analysed based on Gibbs free energy. Moreover, the solidification behaviour of the HEA was studied using the Kurz-Giovanola-Trivedi and the Gaümann models with modifications for multi-component alloys.