<div class="section abstract"><div class="htmlview paragraph">Brake calipers for high-end cars are typically realized using Aluminum alloys, with Silicon as the most common alloying element. Despite the excellent castability and machinability of Aluminum-Silicon alloys (AlSi<i>x</i>), anodization is often required in order to increase its corrosion resistance. This is particularly true in Chlorides-rich environments where Aluminum can easily corrode. Even if anodization process is known for almost 100 years, anodization of AlSi<i>x</i> -based materials is particularly challenging due to the presence of eutectic Silicon precipitates. These show a poor electric conductivity and a slow oxidation kinetics, leading to inhomogeneous anodic layers. Continuous research and process optimization are required in order to develop anodic layers with enhanced morphological and electrochemical properties, targeting a prolonged resistance of brake calipers under endurance corrosive tests (e.g. &gt;1000 hours Neutral Salt Spray (NSS) tests). In this manuscript a lab-scale anodization setup is used to investigate the interplay between process parameters, oxide layer morphology and corrosion protection capability. The influence of high anodization steps (AS) and low rest steps (RS) in pulsed anodization waveforms is investigated with respect to the homogeneity and compactness of the obtained oxide layers. In comparison with a conventional set of anodization parameters, which is taken as a standard, the following level of performance are achieved: 1) increase of the corrosion potential (Ecorr) of +98mV; 2) increase of the anodic breakdown potential (Ebp) of +362mV; 3) reduction of the corrosion rate of a factor six; and 4) a polarization resistance 1.5 times higher. This work identifies key parameters in the anodization of Aluminum-Silicon alloys and propose new electrochemical figures of merit in order to: a) extend the corrosion resistance of future braking systems; and b) evaluate <i>ex-situ</i> the anodic layer electrochemical performance.</div></div>

Investigation of the corrosion performance of friction materials (FMs) plays a central role in: a) evaluating the corrosion resistance of braking pads [1]; b) elucidating galvanic couplings among different braking system components [2]; c) designing FMs with a negligible sticking effect upon coupling with a cast iron brake disc [3]. Corrosion performance can be evaluated by measuring proper electrochemical figures of merit [4] such as the: 1) corrosion potential (Ecorr); 2) corrosion current (Icorr); and 3) galvanic current (Igc); in agreement with a suitable test specification. Nevertheless, particular attention should be paid when measuring these quantities since several experimental details can lead to inaccurate or misleading results. At this regard, the work clarifies the effect of several test parameters (e.g. scan rate, stabilization time, potential ranges, etc.) on the measure of the corrodibility of a reference friction material. Most common errors and their effect on the electrochemical figures of merit are discussed, with the final aim of providing a solid guideline for designing braking pads with a reduced corrodibility. References:[1] Bertasi, F., Mancini, A., Bandiera, M., Pin, S., Casini, A., Bonfanti, A., “Interplay between Composition and Electrochemical Performance at the Pad-Disc Interface”, EUROBRAKE, Manuscript no. EB2019-MDS-018 (Stansted, UK: FISITA, 2019), p. 1.[2] Bertasi, F., Bandiera, M., Bonfanti, A., “Toward a Corrosion Proof Braking System”, SAE Technical Paper, Manuscript no. 2020-01-1625, 2020.[3] Bandiera, M., Mancini, A., Bonfanti A., Pavesi, A., Pin S., Bertasi, F. “Sticking Phenomena at the Brake Pad – Disc Interface: An Open Call for Electrochemists”, CORROSION/21, Manuscript no. C2021-16429, 2021. (under review).[4] Bandiera, M., Pin, S., Bonfanti, A., Bertasi, F., Mancini, A., “Physico-Chemical Characterization of Corrosion Scales in Braking Systems”, CORROSION/20, Manuscript no. C2020-14687, 2020.

<div class="section abstract"><div class="htmlview paragraph">The manuscript firstly overviews the corrosion potentials of several components used in disk-brake systems. Particular attention is devoted to the couplings between materials with different nobility. It is demonstrated that if two materials: a) show a difference in their corrosions potential (E_corr) &gt;100mV; and b) are in electric contact in the presence of an electrolyte; they can form a galvanic couple (GC) which could undergo severe corrosive phenomena. In the second part, the paper focuses on the anodized Aluminium (ANOD-Al)-stainless steel (SS) GC. This couple is investigated since: 1) anodized Al and SS are often comprised in high-end braking systems and typically constitute the caliper body (anodized Al) and several components (springs, pins, screws, metal plates, rods, shims etc.) included; and 2) it shows one of the largest corrosion potential difference among all materials included in a braking system (&gt;500mV). As a consequence, the ANOD-Al-SS appears to be one of the most strategic GC whose careful electrochemical investigation will allow the development of future corrosion-proof braking systems. Addressing this point, the manuscript investigates the effect on the corrosion rate of the distance (<i>d</i>) and the area ratio (A_ratio) between anodized ANOD-Al and SS components using a suitable model system. This approach allows for the first time to obtain design rules based on the corrodibility of different materials with the final aim of customizing the corrosion protection of each brake system component.</div></div>

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