Effect of Heat Treatment on Microstructure and Properties of Al-25Si Wear-Resistant Coatings Sprayed by Supersonic Plasma

In this study, the changes in the microstructure and properties of the Al-25Si wear-resistant coating sprayed by supersonic plasma under different heat treatment conditions (200 °C × 48 h, 200 °C × 96 h, 255 °C × 48 h, 255 °C × 96 h, 300 °C × 10 h, and 300 °C × 20 h) were mainly investigated and analyzed. The results revealed that for the coating microstructure, both Al and Si grains in the coating grew after heat treatment, among which Al grains completed growth just at the beginning of each heat treatment stage, while Si grains grew and coarsened continuously with the temperature rise, with the coarsening rate constant reaching as high as 10.66 × 10−15 m2 h−1. In terms of mechanical properties, the hardness of the coating decreased with the increase in the heat treatment temperature, with a minimum value of (186.0 ± 18.0) HV0.2. As to wear resistance, the wear extent of the coating was aggravated as the heat treatment temperature rose, during which the wear mechanism changed from abrasive wear + slight adhesive wear + slight oxidative wear under a sprayed state into abrasive wear + adhesive wear + slight oxidative wear after heat treatment.