Liquid phase surface melting of AA8011 aluminum alloy by addition of Al/Al2O3 nano-composite powders synthesized by high-energy milling

Poor wettability of particles is an obstacle in formation of sound composite layer via surface melting. Pre-coating of particles with metallic material by different techniques, such as ball milling may enhance the wettability of the particles with molten metal. In this study, composite surface layers containing Al2O3 particles were fabricated on the surface of AA8011 aluminum substrates by tungsten inert gas (TIG) surface melting using preplaced layers of Al/Al2O3 powder mixtures in two different forms: (1) a mixture of 40 wt% Al and 60 wt% of 50 nm Al2O3 powders and (2) a mixture obtained by mechanical alloying of 40 wt% Al and 60 wt% of 60 μm Al2O3 powders. Morphology evolution of powders during ball milling and the microstructure of the fabricated composite layers were studied through conventional characterization techniques, such as optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Microhardness measurements were also performed across the alloyed zone. The results indicated that the layer fabricated by the second route showed a defect free structure with a more uniform distribution of Al2O3 particles in comparison with the layer obtained by the first route. It was also noticed that the uniform dispersion of Al2O3 particles in the fabricated layer increased the hardness to 133 HV which was over 3 times of that of the base metal.