Liquid phase surface alloying of AZ91D magnesium alloy with Al and Ni powders

In this paper, liquid phase surface alloying of AZ91D magnesium alloy was carried out by pre-placing of Al and Ni powder mixture and subsequent tungsten inert gas (TIG) melting process. The effects of TIG processing parameters on both microstructures and resulting hardness were investigated. Microstructures of alloyed layers were studied by optical microscope, and scanning electron microscope equipped with energy dispersive X-ray spectroscopy (EDS) analyzer, and the phases were identified by X-ray diffraction analysis. The microhardness of the surface alloyed layer was also measured. The surface hardness was increased from 80 HV0.1 for AZ91D magnesium alloy to as high as 162 HV0.1 for alloyed sample due to the formation of Mg17Al12 and AlNi3 intermetallic compounds in the alloyed region and structural refinement. Hardness improvement reduced the wear rate of the surface alloyed layer to almost half of that of the untreated substrate.