Growth characteristics and properties of plasma electrolytic oxidation coatings produced in different electrolytes on SiCp/Al composite

Abstract

PEO coatings on SiCp/Al composites generated in phosphate, silicate, and aluminate electrolytes are compared to reveal the effect of the electrolyte composition on the coating formation process and coating performance. The observed significant disparity in spark discharge highlights the considerable influence of the electrolyte composition on the coating growth of the SiCp/Al composite surface. Within the plasma discharge zone, the local temperature ranges are approximately 6000 K–12000 K for silicate electrolyte, 6000 K–10000 K for aluminate electrolyte, and 4000 K–5000 K for phosphate electrolyte. Regarding spark discharge intensity, silicate electrolyte exhibits the highest discharge, followed by aluminate electrolyte, while phosphate electrolyte displays the weakest discharge. Consequently, the resulting surface porosity reaches up to 9.1% for PEO-Si coating, 6.5% for PEO-Al coating, and 4.9% for PEO-P coating. Phase analysis reveals that coatings generated in aluminate and silicate electrolytes tend to consist of crystalline alumina and mullite, whereas the coating formed in phosphate electrolyte predominantly contains amorphous phases and some crystalline mullite. The electrochemical tests demonstrate that the anti-corrosive ability of the coatings follows the order of PEO-Al > PEO-Si > PEO-P. The electrical insulation protection performance of the three coatings is PEO-Al > PEO-Si > PEO-P under comprehensive consideration.