A Comparative Study of Microstructure and Tribological Properties of Electroless Ni-P, Ni-W-P, and Ni-Ce-P Coatings on 6061 Aluminum Alloy: The Role of Heat Treatment

This study conducts a systematic comparison of binary Ni-P, ternary Ni-W-P, and ternary Ni-Ce-P electroless coatings on 6061-T6 aluminum alloy, focusing on the effects of post-plating heat treatment at 300, 350, and 400 °C. The originality of this work lies in its direct comparison of W and Ce doping under identical conditions and its identification of a critical brittle transition that decouples hardness from wear resistance. All coatings achieved peak hardness at 350 °C, with Ni-W-P reaching approximately 1691 ± 45 HV_0.1 due to Ni₃P precipitation and solid-solution strengthening. However, a key finding is the severe embrittlement of the Ni-P coating at 300 °C, where its wear rate increased by over 50 times despite a hardness increase. Treatment at 400 °C degraded wear performance across all systems, likely due to precipitate coarsening and substrate over-aging. The best overall performance within the tested window was achieved with the Ni-Ce-P coating heat-treated at 350 °C for 1 h, which exhibited a fine nodular structure and reduced the wear rate by 98.9% compared to the bare substrate. These results highlight the importance of balancing hardness and toughness, identifying an optimized processing window for enhancing the tribological performance of lightweight aluminum components.