Microstructures of the bonding area in laser cladded Zr-based amorphous alloy coating on magnesium

Abstract

The Zr65Al7.5Ni10Cu17.5 amorphous alloy was laser cladded on magnesium substrates by employing a 5 kW continuous wave CO2 laser. The laser scan rate ranged from 3 to 10 mm/s and the laser output power ranged from 2000 to 4000 W. The typical microstructures in the bonding area of specimens at a scan rate of 3 mm/s or 5 mm/s consist of white Zr rich particles, grayish Mg rich eutectics and gray Mg rich equiaxed dendrites, while a characteristic sharp interface was obtained at a scan rate of 10 mm/s. Neither obvious micro-voids nor porosity is observed in this area, implying a good bonding condition, In addition to the structural features of the microstructure, the resulted molten depth of the substrate upon different scan rate and the laser output power during the bonding process were also investigated to build to a more comprehensive connection between the process conditions and the bonding properties. The growth type of the Mg rich phase in the bonding area was analyzed by using Hunt’s CET model and KGT model and the results showed a good agreement with the experimental results.