Investigation of Ni-P/− SiC coatings on aluminum alloy via aqueous cathodic plasma electrolysis

Ni-P-SiC coatings with different P contents were co-deposited on aluminum alloy directly by cathodic plasma electrolysis. The influences of pulse voltage on microstructure and phosphorus content, solution composition on discharge starting voltage and phosphorus content were studied. Experimental results showed that, with the increase of working voltage from 90 to 130 V, phosphorus content in coatings reduced gradually, while coating surface roughness increased. As H3PO3 content increased gradually, discharge starting voltage on the cathode surface decreases quickly after transient gradual stabilization. SEM observations unveiled that the bonding state between Ni-P coating and substrate is metallurgical and the coating microstructure is fine, uniform, and free of porosity and crack. FE-TEM and EDS results showed that as-received Ni-P-SiC coatings possessed nano crystalline structure. XRD analysis indicated that the phases of as-deposited Ni-P-SiC coating are Ni and Ni3Si0.96B with crystalline states transformed from amorphous phase.