Microstructure evaluation of A356 aluminium alloy laser surface alloyed with Ni-Ti-SiC and Ni-Ti-C

Abstract

Laser surface alloying of A356 aluminium alloy was performed by means of a continuous wave CO2 laser with alloying elements being introduced in the substrate by a stream of powder co-axial to the laser beam. Powder mixtures containing Ni-Ti-SiC and Ni- Ti-C were used to create uniform alloyed surfaces consisting of carbides embedded in a matrix of aluminium with Al-Ni intermetallics. The resulting microstructures were examined by means of optical and scanning electron microscopy, and the various phases were identified by Energy Dispersive X-Ray Spectroscopy and X-Ray Diffraction. Surfaces produced using Ni-Ti-C powders presented a microstructure composed of fine TiC particles dispersed in structures of Al-Ti-Si and Al-Ni intermetallics within an Al-Si matrix. The surfaces produced with Ni-Ti-SiC powder mixtures presented a similar microstructure, with the addition of undissolved SiC particles. The TiC particles in the structures were formed from the in-situ reaction between the carbon or the dissociated SiC and the titanium. The alloyed surfaces gave an increase in hardness compared to the substrate of up to 3.5 times, increasing with the proportion of alloying elements in the structure.