Micro-Arc Oxidation Process And Preparation Antibacterial Compound Coatings On Aluminum Alloy

In order to improve the surface hardness and corrosion resistance of aluminum alloy, and give consideration to good mechanical properties and antibacterial properties, compound treatment on 6061 aluminum alloy was used by micro-arc oxidation （MAO） and electroless silver plating. The compound coatings with high strength, good bonding and antibacterial properties were prepared combined with the advantages of micro-arc oxidation and electroless silver plating technics.The growth process of ceramic coatings was analyzed systematically in different electrolyte systems. Effects of composite organic additives and Na₂WO₄ on the properties of ceramic coatings were discussed. The process of electroless silver plating on ceramic coatings was researched. The microstructure, phase composition and elements were analyzed using SEM, XRD and EDS techniques. The hardness, corrosion resistance, bonding strength and antibacterial properties were tested. Results and conclusions areshown as follows:1. Process parameters systems（1） The optimum process parameters of micro-arc oxidation electrolyte system is Na2SiO3（18 g/L）, Na₂WO₄（5 g/L）, C10H14N2O8Na2（0.8 g/L）, Na3C6H5O7（1 g/L） and NaOH （1 g/L）.（2） The optimum process parameters of electroless silver plating is AgNO3（5 g/L）, NaOH（3 g/L）, NH4OH（45 ml/L）, C2H5OH（15 ml/L）, KNaC4H4O6（11 g/L） and 11.5 of solution pH.2. Ceramic coatings properties（1） Arcing voltage is decreased with the increasing of electrolyte concentration. Arcing energy is reduced. Current density has little effect on arcing voltage that is close related to the types and concentration of electrolyte systems.（2） Ceramic coatings are composed of compact coating and loose coating, mainly containingα-Al₂O₃ andγ-Al₂O₃. The composition of loose coating is restricted to components of electrolyte system. The composition of compact coating is close related to the components of substrate.（3） Under constant current mode, the thickness of ceramic coatings is increased linearly with the increasing of oxidized time. Growth rate remains basically unchanged. Under constant voltage mode, growth rate is increased fast in prophase of oxidation, and increased low in anaphase of oxidation. When oxidized time is more than 5.5 hours, discharge is very weak. The growth of ceramic coatings is almost stopped.（4） Ceramic coatings of micro-arc oxidation have good corrosion resistance which is increased by 12.7 times compared with 6061 aluminum alloy substrate. Its corrosion resistance is further improved by 1.6 times with 5 g/L Na₂WO₄ added into Na2SiO3 electrolyte system.3. Compound coatings（1） The surface morphology of coatings is bright white, coatings are compact, flat and small grain. Silver electroless plating plays an important role in sealing the microporous of ceramic coatings. Compound coatings have good protective properties.（2） Compound coatings have high hardness, the maximum hardness is 1026 HV. Bonding strength between coatings reaches 33.68 MPa, coatings combine each other firmly.（3） Antibacterial test results show that the maximum diameters of inhibition rings of compound coatings are 25.12 mm and 21.56 mm to staphylococcus and escherichia coli, antibacterial effect reaches R grade, and compound coatings have high degree of antibacterial properties.The results show that compound treatment on 6061 aluminum alloy is effective method consideration to mechanical and antibacterial properties by micro-arc oxidation and electroless silver plating technics, high strength compound antibacterial coatings can be prepared with high efficiency, endurance, safety and good bonding properties.