In-situ formation of Sr2SiO4 composite PEO coatings on HPDC AlSi12Cu1(Fe) alloy for enhanced wear resistance and energy efficiency

Abstract

Plasma electrolytic oxidation (PEO) coatings and hard anodizing (HA) were applied to HPDC AlSi12Cu1(Fe) alloy to evaluate their microstructural and tribological performance. Particular attention was given to the influence of the initial surface state, comparing as-diecast and ground (with up to 1 mm of material removed) conditions. PEO was carried out in silicate-based electrolytes, one of which contained strontium aluminate particles. Under PEO conditions, strontium aluminate particles are reactively incorporated into the PEO coating, forming a new phase of strontium silicate, producing a composite ceramic coating (PEOp). The effect of initial surface state was more pronounced for HA than for PEO and PEOp coatings, influencing the coating thickness, growth rate, surface roughness, and wear resistance. PEOp coatings achieved up to ∼23 % energy savings, increased thickness, and enhanced wear resistance compared with PEO. SEM, EDS mapping, and XRD confirm the incorporation of strontium aluminate (SrAl2O4) into the outer porous layer, forming strontium silicate (Sr2SiO4), reducing cavities and surface roughness. Furthermore, SEM-EDS analysis of the worn surface demonstrates that Sr2SiO4 enhanced tribolayer stability, thereby reducing the wear rate and friction coefficient.