Study On The Micro Arc Oxidation Of The Plating Of Aluminum Manganese Alloy On Steel

Micro-arc oxidation technology is a technique for metal surface treatment, which has been developed on the basis of conventional anodic oxidation. The ceramic coatings with excellent wear and corrosion resistance can be obtained on the surfaces of Al, Mg and Ti using such a method. In this thesis, the Al-Mn alloy plating was prepared for the first time on the Q235 steel using a molten-salt electroplating, and was subsequently oxided into Al-Mn micro-arc oxidation ceramic coatings by the aforementioned micro-arc oxidation, which further enhanced the surface performance of the employed steel substrate.In this thesis, a technology for preparing the ceramic coating by micro-arc oxidation was investigated using two electrolyte systens such as silicate and carbonate. The thickness and hardness of the as-prepared ceramic coating have been tested under under a series of process conditions. The morphology and the texture of the as-prepared ceramic coatings surface were characterized using SEM, EDX and XRD, respectively. The corrosion resistance of Al-Mn-ceramic coatings in 3.5% NaCl aqueous solution was evaluated by polarization curves and electrochemical impedance spectroscopy. The relevant experimental results were further verified by a salt spray test.It has been demonstrated that silicate used as an electrolyte could facilitate Al-Mn alloy to form an excellent ceramic coating, which was resistant to breakdown, whereas the electrolyte of carbonate can present a ceramic coating with larger thickness. The micro-arc oxidation process can gradually reduce the number of discharge channels and increase the pore diameter, and can also lead to the formation of some apparent melting marks on the surface of ceramic layer. The ceramic alumina coating formed by micro-arc oxidation were mainly composed ofα-,γ-, andθ- phase as well as some amorphous species. The ceramic coatings of Al-Mn alloy obtained with the as-described two electrolyte in this work can effectively reduce the corrosion rate of the steel substrate, thus significantly enhancing its corrosion resistance.