Microhardness and Microstructure Studies on Laser Surface Alloyed Aluminum Alloy with Ni-Cr

Aluminum alloy LM13 was surface alloyed with Ni and Cr of different compositions (in wt.%) at various laser powers (1 kW, 1.5 kW, and 2 kW) using CW CO2 laser. Microhardness and microstructure of alloyed regions were examined. The study shows that surface alloying is achieved when the laser power is sufficiently high (1.5 kW). Microhardness increases appreciably when the Cr concentration is increased in the Ni-Cr composition. However, in the alloyed region, large variations in microhardness are observed with depth below the surface of the material. Microstructure exhibits needle structure when Ni-concentration is high and undergoes a phase transformation when Cr-concentration is increased. XRD analysis in the alloyed samples shows formation of intermetallic compounds.