Autocatalytic nickel coatings on aluminium with improved abrasive wear resistance

The heat treatment temperature required to maximize the wear resistance of autocatalytic nickel deposits exceeds the age-hardening temperature of aluminium alloys. As a consequence, a careful selection of the heat treatment temperature is required in order to preserve the mechanical characteristics of the aluminium substrate while improving coating performance. The abrasive wear resistance of the nickel-phosphorus/Al 6063-T6 system was evaluated taking into account several criteria, such as: phosphorus (P) content, SiC particle codeposition, and heat treatment. The results of wear resistance were related to the structural changes (i.e. phase transition, grain size) observed by X-ray diffraction for different phosphorus coatings and after the applied heat treatments. With increasing the phosphorus content, the abrasive wear resistance of as-deposited particle-free coatings decreased and their structure changed from a nanocrystalline supersaturated solid-solution of phosphorus in nickel (P less than or equal to 6 wt.%) to an amorphous nickel-phosphorus phase (P greater than or equal to 10 wt.%). The composite coatings with 30-35 vol.% SiC were more wear resistant relative to particle-free coatings. Finally, a heat treatment temperature of 220 degreesC with 1 h holding time proved to further enhance the abrasive wear resistance of low- and medium-phosphorus coatings (particle-free and composites), whereas no improvement was observed for the amorphous coatings. The selected thermal treatment did not affect the hardness of the aluminium substrate. (C) 2000 Elsevier Science S.A. All rights reserved.