Effect of heat treatment on the structure and properties of electrolessly deposited Ni-W-Cr-P alloy coatings on aluminum alloy

摘要

Ni-W-Cr-P alloy coatings were prepared by electroless deposition on Al_9Si compound. The effect of heat treatment on the structure and property of prepared coatings was validly investigated. XRD analysis showed that the as-deposited coatings were Ni-W-Cr-P solid solution. Interestingly, the Ni_3P phase was observed in the samples annealed at 400°C, meanwhile, the heat treatment at 500°C process resulted in the formation of Ni_3P, Cr_(1.12)Ni_(2.88) and Al_(0.983)Cr_(0.017) phases. Two brand new (AlSi)_7Ni_3 and Al_3Ni_2 phases were identified in the coatings annealed at 600 °C. The experimental results reveal that the as-deposited Ni-W-Cr-P alloy coatings exhibit higher microhardness and better corrosion resistance comparing with those of as-deposited Ni-P and Ni-W-P coatings. At higher annealing temperature, the micro-hardness of the Ni-W-Cr-P alloy coatings increased, got to the maximum value at 500 °C, and decreased slightly for the samples annealed at higher temperature. It is worth noting that the corrosion resistance was also remarkably improved by heat treatment.