Laser Surface Alloying of 7075 Aluminum Alloy with Cr, SiC, and Carbon Nanotube Powders

AA7075 is a promising aluminum alloy for the fabrication of structural parts in various sectors including aerospace and marine. To improve the surface properties of AA7075, a CO₂ laser was utilized for surface alloying with a powder mixture of Cr, SiC and carbon nanotube. The influence of laser beam power and scanning speed on the microstructural characteristics, wear behavior, hardness and corrosion susceptibility was investigated for the samples alloyed at constant energy density. The microhardness of the alloyed surface layer got enhanced from 84 to 237 HV, which is approximately 2.8 times than that of substrate material. As a result, the wear rate substantially reduced. The enhanced hardness and wear resistance was due to the formation of hard chromium carbide phases (Cr₃C₂ and Cr₂₃C₆) and grain refinement. The corrosion resistance enhanced with the enrichment of highly dense passive layers of Cr₂O₃, Al₂O₃ and SiO₂. It was noted that high interaction time during alloying is required for getting enhanced hardness with good wear and corrosion resistance.