Browse Publications Technical Papers 2024-01-3038
2024-09-08

Glow-discharge Optical Emission Spectroscopy Study of Cr(III) Sealing in Anodized Aluminium-Silicon Alloys for Brake Component 2024-01-3038

Calipers and pistons for high-end car braking systems are typically realized using anodized Aluminium-Silicon alloys. Indeed, Aluminium-Silicon alloys are light materials with optimal mechanical properties and, when anodized, excellent corrosion and wear resistances. To achieve these top-notch surface properties, the anodizing process is followed by a sealing post-treatment, which significantly improves the corrosion resistance and tunes the tribological properties (e.g., hardness and friction coefficient) of the anodized pieces. Sealing consists in the precipitation of insoluble hydroxides and functional compounds (e.g., corrosion inhibitors) inside the nano-pores of the anodic layer. Nevertheless, sealing might not penetrate through all the nano-porous structure of the anodic layer. Thus, in light of possible post-machining of sealed, anodized components, it appears fundamental to develop a tool to determine the depth penetration of sealing inside the anodic layer. In this context, Glow-Discharge Optical Emission Spectroscopy (GDOES) is a powerful technique, which allows the elemental depth profile analysis of surfaces. Hence, by means of GDOES the work aims at investigate the penetration of a Cr(III)-based sealing in the anodic layer of two Aluminium-Silicon alloys (i.e., EN AC-42200 and EN AC-43200) used in the production of brake components. EN AC-42200 and EN AC-43200 samples are: 1) sectioned from components, 2) anodized at different times to obtain different anodic layer thicknesses and 3) sealed in a Cr(III)-based proprietary sealing solution. Then, GDOES analyses with optimized parameters are performed together with metallographic analyses and Eddy current thickness measurements. The obtained results suggest that, regardless of the anodic layer thickness and the composition of investigated alloy, Cr sealing is not able to penetrate through the entire anodic layer. As a consequence, a gradient in the anodic layer hardness, corrosion resistance and tribological properties is expected and post-machining should be carefully designed. On a broader prospective, this manuscript demonstrates the potential of GDOES analysis in the study of sealing penetration and paves the way for optimized design of braking components.

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