Fabrication Of Super-hydrophobic Layer On The Surface Of AZ31 Magnesium Alloy And Its Corrosion Behavior

Magnesium alloy has a series of advantages such as high strength-to-weight ratios,high specific strength,good machining properties.In order to overcome its defect of active chemical character and poor corrosion resistance,finding an efficient and practical method is meaningful to magnesium's application.This article respectively used one-step electro-deposition and two-step method with pre-treatment and electro-deposition to fabricate super-hydrophobic coatings on magnesium alloy,which show good hydrophobic performance and corrosion resistance.The influence of deposition time,direct voltage and electrolyte concentration on the coatings' microstructure,wettability and corrosion resistance during the preparation process was studied.And the mechanisms of coating formation and corrosion resistance were also analyzed.The influence of micro-arc oxidation,anodic oxidation and hydro-thermal treatment on the coatings' morphologies and properties was studied,and the evolution rules of composite coatings in immersion were also researched.The results indicate that the current density decreases with time in electrodeposition process,which can be divided into two stages corresponding to coatings' nucleation and growth.Together,the micro-nano hierarchical structures and low surface energy of myristic acid calcium give the coatings superhydrophobicity.Process parameters have significant effects on coating's morphologies and properties without affecting its phase composition.The coating has good super-hydrophobicity in initial stage of immersion and it can capture an air layer to prevent the penetration of solution to the substrate.But with the extension of immersion time,the coating's composition changes from myristic acid calcium to hydrate myristic acid calcium.This change leads to decrease in water contact angle and corrosion resistance,and the coating change from superhydrophobicity to hydrophobicity and hydrophily.The results show that process parameters in electrodeposition have significant effects on coating's corrosion resistance.At the deposition voltage 50 V,concentration 0.08mol/L and deposition time 60 min,the coating formed with an appropriate thickness and good hydrophobicity,so it has good corrosion resistance.The coating shows second time constant after 4 days,which represents the corrosion reaction in substrate.Different pre-treatment processes have significant impacts on coating's morphologies and properties,which is closely to the corrosion resistance in immersion.With the effect of pre-treatment layer and coating,the impedance modulus keep increasing in the middle stage of immersion and the composite coatings show steady properties in long time immersion.The anodic oxidation pre-treatment layer can provide the steady corrosion resistance for the whole coating system which shows the highest water contact angle,so this sample has the best corrosion resistance.