Enhanced corrosion resistance of 2024 aluminum alloys with Cr2O3 thin layers by Atomic Layer Deposition

Abstract

This research explores the use of chromium oxide (Cr2O3) thin layers grown by Atomic Layer Deposition (ALD) as protective coating to enhance the corrosion resistance of 2024 aluminum alloys. In order to obtain sufficiently dense and uniform Cr2O3 layers, the ALD process was tailored in terms of alloy surface pretreatment before the main Cr2O3 ALD process. The corrosion resistance of both Cr2O3 coated and non-coated aluminum alloys was evaluated in a corrosive 0.1 M KOH environment using in situ optical microscopy and ex situ surface analysis techniques, including X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and a neutral environment containing chlorides. Findings revealed that the Cr2O3-coated samples exhibited significantly reduced reactivity, highlighting the excellent corrosion protection provided by the Cr2O3 thin films. Although surface analysis revealed the presence of submicron defects within the Cr2O3 layer, which could act as corrosion initiation sites, the occurrence of these defects was mitigated with increasing Cr2O3 layer thickness. Additionally, after the corrosion test, an enrichment of copper and aluminum oxides at the layer surface was observed, suggesting preferential attack at intermetallic phases in corrosive environment.This research explores the use of chromium oxide (Cr2O3) thin layers grown by Atomic Layer Deposition (ALD) as protective coating to enhance the corrosion resistance of 2024 aluminum alloys. In order to obtain sufficiently dense and uniform Cr2O3 layers, the ALD process was tailored in terms of alloy surface pretreatment before the main Cr2O3 ALD process. The corrosion resistance of both Cr2O3 coated and non-coated aluminum alloys was evaluated in a corrosive 0.1 M KOH environment using in situ optical microscopy and ex situ surface analysis techniques, including X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and a neutral environment containing chlorides. Findings revealed that the Cr2O3-coated samples exhibited significantly reduced reactivity, highlighting the excellent corrosion protection provided by the Cr2O3 thin films. Although surface analysis revealed the presence of submicron defects within the Cr2O3 layer, which could act as corrosion initiation sites, the occurrence of these defects was mitigated with increasing Cr2O3 layer thickness. Additionally, after the corrosion test, an enrichment of copper and aluminum oxides at the layer surface was observed, suggesting preferential attack at intermetallic phases in corrosive environment.