Microstructures of alloyed and dispersed hard particles in the aluminium surface

Laser surface alloying of A1200 aluminium alloy was carried out using a 4.4 kW Nd:YAG laser. Powder mixtures of SiC and TiC hard particles were injected into the laser generated melt pool on the aluminium substrate using a commercial powder feeder. The uniformly dispersed particles penetrated approximately 2 mm into the surface. The microstructure, composition and the phases in the alloyed layer were investigated. The analysis showed that the layer consisted of distinct SiC and TiC particles embedded in the layers. The scanning electron microscope (SEM) showed that a good metallurgical bond between the particles and substrate was formed. The X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analysis techniques were employed in the identification of the phases. The layer also contained solidified TiC dendrites, plate-like Al₄SiC₄ and some precipitates of Ti₅Si₂. The hardness of the layer was three times that of the un-reinforced substrate material.