Influencing factors and process optimization of Al 25Si coating prepared by inner-hole supersonic atmospheric plasma spraying

For inner-hole parts, the main positions bearing load are their inner walls, which are prone to strain, wear, corrosion and other damages during use. Aluminum‑silicon (AlSi) coating (Al25Si) with excellent properties can be prepared through inner-hole supersonic atmospheric plasma spraying (SAPS) technology to provide reliable protection for inner-hole parts. In this paper, a study was conducted to find out how spray gas parameters, spray electrical parameters, and spray distances influence the temperature and velocity of flying particles during the process of preparing Al25Si coatings through inner-hole SAPS. Meanwhile, the coating preparation process was also optimized in this study. Through analysis and experimental verification, the optimal process parameters for preparing the coatings are as follows: The total gas flow is 115 L/min, the hydrogen (H2) content is 7.5 %, and the spray voltage, spray current, and spray distance remain at 86 V, 430 A, and 90 mm. Under these spray parameters, the particle temperature and flight velocity are 2698.7 °C and 473.9 m/s, respectively, while the porosity and microhardness of the coating are 0.79 % ± 0.56 % and 267.09 ± 14.85 HV 0.2, respectively.