The synergistic effects of heat treatment and anodizing on the blackening phenomenon of DMLS-built AlSi10Mg components for aerospace applications

Abstract

AlSi10Mg alloy components were produced via direct metal laser sintering and subsequently subjected to T6 heat treatment (430 °C–500 °C with aging at 140 °C) and stress-relieving (SR) cycles between 250 °C and 290 °C, followed by anodizing to enhance corrosion performance. The investigation targeted aerospace applications such as elbows, breathers, and fuel line connectors. Microstructural characterization using field emission scanning electron microscopy coupled with image analysis quantified the size, distribution, and morphology of silicon particles, enabling correlation with mechanical and electrochemical responses. The as-built alloy measured a hardness of 160.3 BHN, which decreased to 120.5 BHN after SR at 250 °C due to silicon refinement, while T6 and SR treatments led to 53% and 50% hardness reductions, respectively. Electrochemical testing in 1Molar H₂SO₄ showed that the corrosion rate decreased from 0.08256 mm/year in the as-built state to 0.0004044 mm/year after T6 + anodizing that forms an oxide layer. An optimized SR condition at 260 °C yielded 112.05 BHN with ultra-fine silicon particles (7.28 × 10⁻⁴ µm) and reduced the corrosion rate from 0.16562 to 0.0035002 mm/year after anodizing, underscoring the process suitability for critical aerospace applications.