Two step coating of a hypereutectic PM Al-Si alloy

The aim of the present work was to combine the high strength of Al-Si alloys produced via Rapid Solidification (RS) and Spray Forming (SF) with a wear resistant surface coating, designed for high temperature use. The surface coating, composed mainly of nickel and chromium, was applied in a two step process: plasma spray followed by laser surface alloying using a diode laser. The microstructure and hardness of the surface coating were analysed. In the Al-Si alloys produced via Rapid Solidification, gas bubble formation was observed during the laser alloying process. In the Spray Formed alloys, globules of the coating material and a needle-like microstructure formed, in detriment to the mechanical properties of the alloyed layer.