Formation and Corrosion Resistance of Crack-Free Chromate Conversion Coatings on SLM AlSi10Mg Surfaces

Selective laser melting (SLM) technology has gained significant attraction in advanced transportation, aerospace, and other industries due to its remarkable capability to fabricate functional, intricate, and sophisticated components. While numerous studies have investigated the mechanical properties and corrosion performance of SLM-produced materials, limited attention has been given to understanding its corrosion protection mechanisms and the feasible surface treatments applicable to it. Moreover, the anti-corrosion chromate conversion coatings (CCCs) formed on SLM alloy surfaces by the conventional chemical conversion process often crack, posing a significant challenge for practical applications of SLM alloys. This study aims to investigate the preparation conditions and corrosion resistance of CCCs on SLM AlSi10Mg samples compared to those on conventionally cast aluminum alloy samples. The microstructure and composition of the sample surface layer after each process step of CCC formation were analyzed using scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDX). Electrochemical tests were conducted to evaluate the corrosion resistance of the CCCs. The results indicate that pretreatment processes involving acid or alkaline solutions can form specific nanostructures on the surfaces of SLM samples. These structures facilitate the uniform distribution of reaction products during the conversion reaction and thereby preventing the formation of macroscopic cracks during drying. The self-corrosion potential of the crack-free CCCs on the SLM samples was higher than − 1.002 V, and the corrosion current density was smaller than 2 × 10−7 A/cm2. The fitted impedance was as large as 1.933 MΩ/cm2. The surface corrosion resistance of the SLM AlSi10Mg alloy treated by the proposed conversion process was comparable or even superior to that of conventionally cast aluminum coated with CCCs.