Session Details
Session 11: Corrosion & Wear Deposit Coatings
Abstract Number:
54
Al and AlMn alloys were studied as alternative coatings to cadmium coatings. The AlMn alloy offered better corrosion protection than the Al layers, pristine or passivated, and this result was confirmed by the polarization resistance values and lower corrosion current densities obtained by linear sweep voltammetry and EIS measurements. The alloy containing 40 at% of Mn offered the best corrosion resistance for steel; it was even superior to a passivated Cd layer.
Topics:
Corrosion or Wear Deposits/Coatings
General Surface Finishing
Al and AlMn alloys were studied as alternative coatings to cadmium coatings. The electrolyte used in this study consisted in a mixture of AlCl3 and [EMIm]Cl (1-methyl-3-ethyl-imidazolium chloride) in a molar ratio of 2:1, in which 0.2 and 0.4 mol/L MnCl2 were dissolved. All the measurements were performed inside a glove-box filled with Ar.
The electrodeposition of Al and of AlMn alloys occurs with a current efficiency close to 100% from the electrolytes chosen. There was a significant difference between the morphology of the Al layers and that of the AlMn alloys. The Al layers consist of microsized grains, while the AlMn alloys are much smoother and more compact. One can also tune the morphology of the deposits by tuning the current density. Thus, at low current densities, below 5 mA/cm², one could obtain rough layers, while smoother ones were deposited at current densities above 6 mA/cm². Al films were crystalline, while the AlMn alloys were often amorphous.
Al and AlMn films showed good corrosion protection properties and can be used as alternative coatings to Cd. The AlMn alloy offered better corrosion protection than the Al layers, pristine or passivated, and this result was confirmed by the polarization resistance values and lower corrosion current densities obtained by linear sweep voltammetry and EIS measurements. The alloy containing 40 at% of Mn offered the best corrosion resistance for steel; it was even superior to a passivated Cd layer.
This study shows that dense and fine-grained Al and AlMn layers can be plated from ionic liquids. Their corrosion behavior in 3.5% NaCl proved to be comparable to that of cadmium. However, in order to make this process attractive for industry, one should further optimize the plating rate and reduce complexity of plating procedure.