Studies On Synthesis Of Superhydrophobic Coatings On Magnesium Alloy And Their Corrosion Resistance Performance

Magnesium alloy is one of the most important structural materials,and magnesium alloys have been available to aerospace,automobile,military and electronic industries,due to their characteristics of low weight,low density,high strength,good thermal/electrical conductivity and excellent castability.However,due to their high chemical and electrochemical activity,magnesium alloys corrode easily,which greatly restricts the applications of magnesium alloy under some special conditions.superhydrophobic coatings can reduce the contact of substrate with water,so that a superhydrophobic coating would be an effective way for magnesium alloy anti-corrosion.In recent years,research has focused on fabrication of superhydrophobic surfaces on Mg alloy for corrosion protection.In this paper,Mg alloys acted as the research objects,and various different synthesis methods,such as:microwave-assisted synthesis method,hydrothermal synthesis method and solution immersion method,have been developed to fabricate superhydrophobic films with certain coarse structures.The morphologies,structures and compositions of superhydrophobic films were characterized by XRD,SEM,TEM,FT-IR and XPS,respectively.In addition,corrosion resistance performance of superhydrophobic films were investigated by electrochemical potentiodynamic measurements and electrochemical impedance spectroscopy.Hierarchical structure flower-like Ni(OH)2 fims,which based on electroless nikel films on Mg alloy AZ31,were fabricated by a simple and rapid non-pressurized microwave-assisted synthesis method on AZ31 magnesium alloy.After modification with fluoroalkylsilane,the films exhibited good superhydrophobic properties with a static water contact angle of 161°.After coated with as-prepared superhydrophobic films,the corrosion current density of Mg alloys reduced by more than three orders of magnitude,and the charge transfer resistance increased 50.2 Ω cm2 from to 9.302×103 Ω cm.Hierarchical structure hydroxyapatite fims were fabricated by a simple hydrothermal synthesis method on AZ31 magnesium alloy.Reaction temperature,reaction time and their effects on morphologies of hydroxyapatite fims were investigated,and it was confirmed that the hydroxyapatite fim possessed the best morphology under the condition reaction temperature was 90 ℃ and reaction time was 6 h.The formation mechanism of the hierarchical structure hydroxyapatite fims was explored briefly.After modified with decylphosphonic acid,the as-prepared hydroxyapatite fims obtained superhydrophobic property with a static water contact angle of 160°.According to the electrochemical testing analysis results,after coated by as-prepared superhydrophobic films the corrosion currentdensity of Mg alloys reduced 8.663×10-5 from to 5.052×10-8,which means that the corrosion rates of Mg alloys decreased significantly.And the radius of electrochemical impedance spectroscopy capacitive loop increased almost three orders of magnitude.The superhydrophobic film exposed to 3.5 wt.%NaCl solution for 5 days,the radius of electrochemical impedance spectroscopy capacitive loop was about 1×104 Ω.Mg(OH)2 films with the uniqe single stage spherical particles structure was successfully fabricated on the surface of magnesium alloy AZ31 by a simple hydrothermal synthesis method that utilized the oxidation of hydrogen peroxide.In the process of the formation of magnesium hydroxide membrane,on the one hand hydrogen peroxide accelerated the formation of Mg(OH)2 films,on the other hand hydrogen peroxide decomposes into O2 and O2 gas played the role of template for the formation of single stage spherical particles structure magnesium hydroxide film.After covered with fluoroalkylsilane molecules,the as-prepared single stage structure Mg(OH)2 films exhibited excellent superhydrophobic property with a static water contact angle of 164°.The as-prepared superhydrophobic films could make the corrosion current density of Mg alloys reduced by four orders of magnitude.At the same time,combined with the electrochemical impedance test results it could know that superhydrophobic fims could siginificant reduce the corrosion rates of Mg alloys exposed to corrosive medium.Hierarchical structure szaibelyite films were fabricated by a simple template-free hydrothermal synthesis method on AZ31 magnesium alloy.And the as-prepared szaibelyite films possessed a unique micro-spherical particles structure that constructed by many nano-fibers.The formation process of the as-prepared szaibelyite films was investigated by XRD,SEM and TEM,and a possible mechanism for formation of the hierarchical structure of the fibrous szaibelyite films was discussed.After modification with fluoroalkylsilane(FAS),the films exhibited advantageous superhydrophobic properties,and under the condition of reaction time was 5 h the szaibelyite films possessed the best hydrophobic performance,with a static water contact angle of 166° and a sliding angle of 2°.The corrosion inhibition efficiency of the as-prepared szaibelyite films could be reached 99,69%.And The superhydrophobic film maintained excellent corrosion resistance performance,after immersion in a corrosive medium(3.5 wt.%NaCl aqueous)for 32 days.A simple and convenient one-step solution immersion method was adopted to directly construct hierarchical structure superhydrophobic films on Mg-Li alloys.The constituent of the as-prepared superhydrophobic films was Mg[CH3(CH2)7PO3],that confirmed by EDS,XPS and FT-IR.And the formation mechanism of the hierarchical structure superhydrophobic films was explored briefly.After coated by the as-prepared superhydrophobic films the corrosion resistance performance of Mg-Li alloys improved significantly.In addition,after exposed to 3.5 wt.%NaCl solution for 7 days,the impedance modulus values of the superhydrophobic Mg-Li alloy was 1.2×104 Ω,this show that the as-prepared superhydrophobic film possessed good durability.