The Study On The Preparation And Corrosion-Resistance Of Mg-Al Pseudo Alloy Coating On The Aluminum Alloy Surface

With high specific strength,specific rigidity and easy forming and machining,aluminum alloys bear outstanding advantages over the strictly limited structures on weight.Aluminum alloys are of high corrosion-property due to the naturally formed Al₂O₃ oxide film on the surface,In the ocean,Most of the aluminum alloys,especially the high-strength aluminum alloys,are subject to pitting,slot corrosion and stress corrosion under sea circumstances,thus the long-period applications of aluminum structures in ocean engineering are limited.To improve the corrosion-resistance properties of aluminum alloys,the research on developing a new surface treating technique is becoming important for broadening apply area of aluminum alloys.Al coats formed on the surface of 6061 aluminum alloy were obtained by arc spraying equipment,Epoxide resin sealing were conducted.Four Mg-Al pseudo alloy coatings which are of different Mg content were obtained on 6061 aluminum alloy matrix with a arc spraying process of magnesium and aluminum heterogeneous wires,subsequent heat treatments and epoxide resin sealing were conducted.The microstructure,porosity and pattern of coats were analyzed by metallurgical microscopy and scanning electron microscopy(SEM),electron probe.Effects of heat treatments on structure and properties of Mg-A1 Pseudo Alloy Coatings were studied.The corrosion resistance property of coating layer in 5%NaC1 solution was tested by means of electrochemical tests,immersion tests and neutral salt spray tests,and corrosion products were analyzed by X-ray diffraction tester.The results show that pure aluminum layer of well-proportioned and dense microstructure and low porosity can be obtained on the surface of aluminum matrix material,the bonding type between the layer and the matrix is mechanical gomphosis.The corrosion resistance improved a lot after layer plugging.Moreover,the layer holds no cathodic protection effects against the matrix.Arc spraying process of magnesium and aluminum heterogeneous wires can be gained by adjusting the parameters such as spray voltage and current.Good Mg-Al pseudo alloy coatings were obtained under low voltage and low current.Before the heat treatment,the Mg layer and Al layer overlaps mutually,and the four coatings bear low corrosion potential which forms cathodic protection to matrix alloy.However,the corrosion-resistance properties of the four coatings are poor,no matter the sealing treatment is processed or not.After heat treatment,the corrosion-resistance properties of the four coatings improve obviously and become higher with sealing treatment processed.With the Mg content of 28.6%,not only the corrosion-resistance property of the coating increases,but also electrochemistry property becomes stable,which poses cathodic protection to the matrix alloy.Analysis shows that a large amount of intermetallic compound(β-Al₁₂Mg₁₇ phase and Al₃Mg₂ phase) formed,which changed the corrosion-resistance property of the coating after heat treatment.Mg-Al pseudo alloy coatings protect the aluminum alloy in two different ways:Mechanical separation and sacrificial anode protection.