Micro-arc Oxidation Growtn Mechanism And Layer Performance Of Al-si Alloy

Aluminum-silicon alloys are widely used in the manufacture of Car engines due to their excellent mechanical properties,physical properties,and processing properties.However,high-acid-alkalinity applications require that the alloy surface has strong corrosion resistance.Micro-arc oxidation technology can produce a smooth and dense ceramic layer on the surface of the alloy which for improve the corrosion resistance in the use environment effectively and increase its service life.In this paper,1060 pure aluminum,ZL101,and ZL102 alloys with different silicon contents in aluminum alloys were chosen to investigate the effect of the content on the reaction process by comparing the film growth rate,thickness,roughness,cross-sectional morphology,hardness,and corrosion resistance during the reaction;In order to further determine the influence of the size of the eutectic silicon phase on the micro-arc oxidation reaction,the ZL101 alloy was subjected to modification treatment with Na to refine the eutectic silicon phase in the matrix for investigating the influence mechanism of the eutectic silicon phase size;in order to find a simple and effective process method capable of improving the quality of the ZL102 alloy film layer,three kinds of surface treatment methods,namely mechanical grinding,acid etching,and pre-blasting,were selected respectively.The surface morphology and element content changes after pretreatment were analyzed by SEM and EDS,and the growth rate and film quality were sequentially compared to evaluate the pros and cons of pretreatment method.Studies have shown that the growth rate and film quality of the micro-arc oxidation film will continue to decrease as the silicon content in the alloy matrix increases.At 10 min,the average thickness of pure aluminum specimen is about 8.33 ?m and the average roughness value is 0.93.When the silicon content is increased to 12.95%,the average thickness of ZL102 alloy is reduced to 6.75 ?m.Similarly,the average roughness is reduced to 0.80 ?m.During the anodization stage,different oxidation reactions occur in the silicon-rich region and the aluminum-rich region on the surface of the substrate.The Al2O3 film is mainly formed on the Al matrix,and a thin Si-O compound is formed on the eutectic silicon.The arc discharge takes precedence on the sites of Al2O3;Using Na to modify the ZL101 alloy,the experimental results show that the film growth rate is always higher than that of the original alloy in 20 min,and the surface discharge holes are more uniform,but there is no big difference in phase composition.The hardness and corrosion resistance of the alloy film after deterioration are improved.The ZL102 alloy was pretreated by mechanical pretreatment,pickling,and sandblasting,followed by micro-arc oxidation in the silicate electrolyte.The experimental results show that the pretreatment method has a great influence on the micro-arc oxidation film formation of ZL102 alloy.The film formation rate is in the following order:pickling sample>mechanically polished sample>sandblasted sample;Using a mixed solution of hydrofluoric acid and nitric acid(volume ratio 2:1)to pickle the ZL102 alloy for 60 s,the surface Si element content can be reduced to 2.02%.The Electrochemical curves and impedance tests have shown that the corrosion resistance of the film after sandblasting is the best.