Growth of Porous Alumina Layer and Cerium Sealing of Al7xxx/SiC Composite for Structural Lightweight Alloy Corrosion Resistant Application

Abstract

AMC (Aluminum Matrix Composite) as a main material for automotive and aircraft applications has the keyadvantage that islighter thanaluminumalloys. So, it can be ascertained that fuel comsumption forthoseapplicationswill be reduced. However, AMC materials are generally suceptible to galvanic corrosion due to galvanic reaction between aluminum matrix and reinforcement, and the formation of microstructure at matrix/reinforcement interface as well. Anodizing is the most effective surface modification method in order to protect AMCs surfaces. This process produces porous anodic coating which has the characteristics of high corrosion resistance and hardness layer. However, the presence of reinforcement particles in AMC hinders the initiation and growth of the protective oxide layer by forming cavities and micro crack. Therefore cerium sealing has been done to remedy the poor anodic film in order to further enhance the corrosion resistance in aggressive circumstances. The material studied in this research was AMC Al7xxx/SiC. Anodizing process were conducted in H2SO4solution at current densities 15, 20, and 25 mA/cm2at 0°C for 30 minutes. Subsequently, continuedwithelectro lesssealinginCeCl3.6H2O+H2O2solutionat room temperature atpH9 for 30 minutes. The morphologies of anodic coating and sealing layer were examined by means of FE-SEM, the corrosion resistance of composites was estimated in a 3.5 wt.% NaCl solution by potentiodynamic polarization test. Coating process conducted by anodizing and cerium sealing in various of anodizing current densities at 0°C results in protective layers which lead to the decreasing of corrosion rate and current density up to four orders magnifications than that of bare and anodizedAl7xxx/SiCcomposite.

An Analysis of the Electrolyte Resistivity Effect on the Pore Diameter and Pore Density of Anodic Aluminium Oxide (AAO) Films Produced by Single-Step Anodization

“…Temperature plays an important role during the anodizing process and significantly affects the morphology of porous AAO (Sulka & Parkoła, 2007;Theohari & Kontogeorgou, 2013). Our previous study showed that an appropriate anodizing temperature produced a porous morphology with good adhesion properties for further coating (Rizkia et al, 2014;Rizkia et al, 2015). Higher anodizing temperature resulted in higher current density and the chemical dissolution of the oxide surface, resulting in porous AAO with wider pores and thinner pore walls (Sulka & Parkoła, 2007;Zahariev et al 2008;Aerts et al, 2009;Aerts et al, 2010Zaraska et al, 2013Kao & Chang, 2014).…”