Trivalent chromium conversion coating on AA2024‐T3 used in aeronautical and aerospace industry

Abstract

Significant research has been conducted to replace the chromium(VI)‐based surface treatments, and some commercial substitute systems are now available and needs to be tested to evaluate their performance and to know how they comply with the required specifications. The anticorrosion properties provided by a commercially available trivalent chromium‐based product—PreCoat A32—when applied to AA2024‐T3 aluminium alloy substrates were evaluated in this work and compared with those obtained with a chromium(VI)‐based pretreatment well‐recognized reference (Alodine 1200S). The morphology and elemental composition of the conversion coatings were investigated by high‐resolution microscopy and energy‐dispersive X‐ray analysis, respectively, being the wettability of the modified surface measured by contact angle goniometry. The data obtained reveal that PreCoat A32–treated surfaces are more apt to receive aqueous paint schemes than those healed with Alodine 1200S. The corrosion resistance of the treated samples was monitored by potentiodynamic polarisation assays and electrochemical impedance spectroscopy analysis, revealing that PreCoat A32 coatings provide improved corrosion protection for AA2024‐T3. The corrosion resistance effectiveness of PreCoat A32 was also confirmed in trials realised in salt‐spray chamber, humidity tests, and thermal cycling assays, where more severe exposure conditions were simulated. The gathered data clearly indicate that the PreCoat A32 brings together the mandatory qualities to successfully substitute the conventional and undesirable chromium(VI)‐based treatments, in aeronautical and aerospace industry.