Laser surface heat treatment of electroless Ni–P–SiC coating on Al356 alloy

• Laser treatment of Ni–P–SiC coating produced a nanocrystallined composite coating.
• Ni3P–SiC coatings did make a crystalloblastic transformation at 60 W laser power.
• The hardness of the coating increased about 28% after laser heat treatment.

Electroless Ni–P–SiC coatings are recognized for their hardness and wear resistance. In the present study, electroless Ni–P coatings containing SiC particles were co-deposited on Al356 substrate. Laser surface heat treatment was performed using 700 W Nd:YAG pulsed laser. Effects of different laser operating parameters, such as laser scan rate, laser average power and defocusing distance on microstructures were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The results of microstructural characterization indicated that the laser treatment under different operating conditions produced composite coating contained nanocrystallined Ni-based matrix with SiC particles Ni3P, Ni12P5, Ni5P2, Ni8P3 precipitates. The microhardness measurements showed that the hardness of the coating was increased up to 60%, due to laser heat treatment, without effect on base metal.