Abstract

The manuscript investigates new waveforms for pulsed anodization of Aluminum Silicon alloys (AlSix) and demonstrates: 1) an effective reduction of the anodic layers porosity degree; 2) an enhancement of the thickness homogeneity; and 3) a boost of the corrosion protection capability; of the obtained coatings.

The interplay between process parameters (e.g. current/potential waveforms), oxide layer morphology and corrosion resistance is investigated by means of several techniques.In particular, metallography, voltammetry and contact angle methods are used in order to correlate the electrochemical figures of merit (corrosion potential, corrosion current, breakdown potential and polarization resistance) with the layer morphological features.

It is concluded that the careful optimization of the anodization process can lead to the development of oxide layers with an enhanced corrosion resistance. In particular, the following level of performance on anodized AlSi7 is achieved: corrosion potential (Ecorr) = −285mV vs. SCE, corrosion current (Icorr) = 0.08nAcm−2, breakdown potential (Ebp) = +778mV vs. SCE and polarization resistance (Rp) = 215MOhm·cm −2.

1) Introduction

Brake efforts in new electric vehicles are strongly reduced due to the progressive evolution of regenerative braking.1 As a consequence, the development of braking systems with a corrosion resistance as long as the vehicle life is a primary point among brake system producers.2,3,4,5

At this regard, brake calipers for high-end cars, which are typically realized using Aluminum-Silicon alloys, can face severe corrosive phenomena in Chloride-rich environments and anodization of these components is often necessary.2,6 In spite of this, anodization of Aluminum alloys comprising a high Silicon content can be a particularly challenging task due to the presence of eutectic Silicon dendrites with poor electric conductivity and sluggish oxidation kinetic.7 As a results, anodic layers obtained under uncontrolled conditions can result in: a) poor thickness homogeneity; and b) presence of porosity and surface cracks; which render the coated parts unable to withstand to galvanic couplings and atmospheric corrosion events.4

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2021. Association for Materials Protection and Performance (AMPP)
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