| Nickel coating,one of the most important protective decorative coatings,is widely used on metals surfaces that in close contact with hunman in daily life.However,after prolonged contact with the human skin,the nickel coating would be easily corroded by human sweat,causing nickel release and allergy to the human body.With the development of society,contact between human and metals will become more frequent.For safety,international regulations have been proposed to limit the release of nickel from metal materials that are in close contact with the human body.In order to satisfy this regulation,reducing or even eliminating the amount of nickel released from the coatings,especially the research work on replacement for nickel coating,has great significance in engineering application and scientific research.In order to solve the problems caused by nickel released from nickel coating,this paper innovatively proposed to use the aluminum-manganese alloy coating as a replacement of nickel coating.The coating is completely free of nickel elements,fundamentally eliminating the harm of nickel release.In this paper,electrodeposition from ionic liquid was used to prepare aluminum-manganese alloy coatings with different crystal structures.The effect of passivation treatment and brightener on the properties of the coatings were studied.Photographic method was used to compare the mirror effect on the surface of the coatings.The roughness tester,the glossiness tester and the electron microscope were used to analyze the macro and micro characteristics of the coatings.The micro hardness tester was used to analyze the hardness of the coatings.And the corrosion resistance of the coatings in artificial sweat was studied by static immersion corrosion test and electrochemical test.Results showed that the crystalline aluminum-manganese coating electrodeposited from AlCl3-EMIC-MnCl2 ionic liquid was uniform and dense,and had good adhesion with the substrate.The coating had uneven general corrosion in artificial sweat.The average corrosion rate was 0.0056 mm/a,which was about one-third of the pure aluminum coating.According to the ten-level standard of metal corrosion resistance,it was a Level 3‘very corrosion-resistant material'.In this paper,the corrosion mechanism of aluminum-manganese alloy coating in artificial sweat was proposed for the first time.Chloride ion in artificial sweat destroyed the passivation film on the surface of the coating.Then the coating was corroded and metal ions were released.These metal ions formed a complex with lactic acid and subsequently turned into a precipitate as the pH of the solution changed,accelerating the dissolution of metals.The corrosion products were mainly Al?OH?3,while Mn was rarely corroded.Chromium-free passivation treatment could reduce the corrosion current of the coating to one-third of that of the unpassivated coating,and improve the corrosion resistance of the coating.There were cracks in the passivation film,and the decorative property of the coating was not improved.A mirror bright coating with fine crystal grains in the same orientation was obtained after adding brightener into the electrolyte.The decorative property of the coating was improved.Compared with the coating without brightener,the corrosion resistance level was improved by one level and the brittleness was increased.The amorphous aluminum-manganese alloy coating obtained by electrodeposition in AlCl3-EMIC-MnCl2 ionic liquid had a good mirror effect.Hardness of the coating was 6.72±0.41 GPa,which is higher than Ni coating.General corrosion occurred in artificial sweat.The average corrosion rate was 0.0024 mm/a,which was a Level 2‘very corrosion-resistant material'.The corrosion current density of the coating in artificial sweat was 9.6×10-7 A/cm2,which was similar to the bright nickel coating.The corrosion potential was-0.99 V vs.SCE.The coating would serve as a sacrificial anode protection to the substrate whose corrosion potential is more negative than nickel coating and more positive than amorphous aluminum-manganese alloy coating. |
PDF Full Text Request