Effects Of Process Parameters And Ce（NO₃）₃ On Morphology And Properties Of Micro-arc Oxidation Coating On 2A12 Aluminum Alloy

2 A12 aluminum alloy has advantages of low density,low melting point,easy to process and shape,certain strength and good abrasion resistance.It is widely used in aviation,military and other fields,but it has low surface hardness and poor corrosion resistance.Its application is subject to certain restrictions.By using of micro-arc oxidation technology,the coating which situ-growed on the substrate of aluminum alloy can obtained.It can improve its surface quality and performance,and expand the application area of aluminum alloy.A self-made micro-arc oxidation equipment was used in this paper.In the constant pressure mode,the control variable method were used to investigate the effects of input voltage,pulse frequency and duty ratio on micro-arc oxide coating morphology and properties in the basic electrolyte composition which ingredient is 10 g/L Na₂Si O₃,2 g/L Na OH,1 g/L EDTA-2Na.And finally determined the optimal parameters.Under these parameters,added different concentrations of Ce（NO₃）₃additive to the basic electrolyte,and studied the effects of its content change on the micro-arc oxide coating morphology and properties.The results show that the main component of the 2A12 aluminum alloy micro-arc oxide coating is Al₂O₃.The surface of the coating has a typical loose and porous"volcano jet"morphology.The pores have different sizes.There are many sintered particles around them.When the input voltage increases,the thickness of the coating increases,and the pores on the surface increase first and then decrease,the Al₂O₃phase increases,the hardness increases first and then decreases,the corrosion resistance first increases and then weakens.When the input voltage is 440 V,the coating is relatively good,the thickness is 24.0μm,the hardness is 335.4 HV,the self-corrosion potential is-0.5548 V and the self-corrosion current is 0.275μA.When the pulse frequency increases,the thickness of the coating decreases,the pores on the surface gradually decrease,the surface flattens gradually,the Al₂O₃ phase decreases,the hardness increases first and then decreases,and the corrosion resistance first increases and then weakens.When the pulse frequency is 200 Hz,the coating is the best,the thickness is 20.2μm,the hardness is 340.0 HV,the self-corrosion potential is-0.5179 V and the self-corrosion current is 0.166μA.When the duty ratio increases,the thickness of the coating increases,and the surface holes increase first and then decrease,more and more"worm-like"gullies appear,the Al₂O₃ phase increases,the hardness increases first and then decreases,and the corrosion resistance first increases and then decreases.When the duty ratio is 30%,the coating is the best,the thickness is 27.0μm,the hardness is 355.4 HV,the self-corrosion potential is-0.5085 V and the self-corrosion current is 0.129μA.Ce（NO₃）₃ additive promotes the micro-arc oxidation process on the surface of the substrate and improves the surface quality of the coating by improving the conductivity of the electrolyte.With the increase of Ce（NO₃）₃ content,the thickness of the coating increases first and then decreases,the pores on the surface increases first and then decreases.The phase composition of the coating is Al phase and Al₂O₃phase.The content of rare earth element is little,so there is no rare earth phase.The hardness of the coating increases first and then decreases.The corrosion resistance increases first and then weakens.When the Ce（NO₃）₃ concentration is 0.20 g/L,the thickness is 34.6μm,the Al₂O₃ phase is more,the hardness is 388.9 HV,the self-corrosion potential is-0.4868 V,the self-corrosion current is 0.058μA.All in all,after adding Ce（NO₃）₃ additive,the quality of the coating is improved compared with that of the basic electrolyte.When the additive content is 0.20 g/L,the comprehensive performance of the coating is the best.