Study On The Preparation And Corrosion Resistance Of The Micro-arc Oxidation Film Of In-situ Tib₂/a201 Composite

In-situ TiB₂/A201 composite is a new lightweight high-strength cast aluminum matrix composites.However,the corrosion resistance of the composite is poor,and the surface treatment is difficult.When the composite is used in high-speed flow conditions,it is necessary to enhance the corrosion resistance in Cl^?environment and corrosion resistance to cavitation,which is a serious challenge to the surface protection of the composite.The micro-arc oxidation?MAO?film has good metallurgical bond with the substrate,and high hardness.Therefore,the MAO film is likely to have strong resistance to cavitation erosion.The aim of this project is to prepare high quality MAO film with high corrosion resistance.The project has optimized the preparation process,and studied the corrosion resistance of the MAO film,which can provide practical guidance for the corrosion protection of TiB₂ particles reinforced composites.The in-situ TiB₂/A201 composite has been set as the research object of this paper.The MAO surface treatment has been applied to TiB₂/A201composites with the optimization of the MAO procedure.Meanwhile,the MAO behavior and the microstructural evolution have been studied.In addition,the corrosion resistance properties of MAO film to Cl^?corrosion and cavitation have been investigated.The main findings are as follows:?1?All of the three kinds of electrolyte systems?sodium silicate,sodium phosphate and sodium aluminate?can fabricate MAO films on the surface of TiB₂/A201 composites.Among these films,the MAO film prepared in sodium aluminate electrolyte system has the lowest porosity?3%?,the highest surface hardness?1265HV?,moderate growth rate?0.6¹.4?m/min?,and been considered to own the best comprehensive performance.?2?Different from the common MAO U-t curves,the MAO U-t curve of TiB₂/A201 composite in aluminate-based electrolyte has two plateaus.Meanwhile,the MAO procedure presents four stages.Stage I:the cell voltage quickly climbs up.The TiB₂ particles on surface are oxidied and a passive film is formed on the surface.Stage II:the cell voltage steps into the first plateau.Accordingly,a crystalline alumina film appears on the surface of composite.Stage III:the cell voltage climbs again.This phenomenon is connected to the repair of the“flaws”in oxide film.Stage IV:the cell voltage steps into the second plateau.In this stage,the oxidation current travels through the oxide film by micro-arc discharges.?3?The caviation erosion of the TiB₂/A201 composites after MAO exhibites three stages.?A?In the initial of cavitation erosion,the"nodules"and"craters"on the surface have been firstly destroyed,and the mass has lost severely.?B?Cavitation pits appear on the film and gradually accumulate,causing the exposure of substrate finally.At this point,the mass loss gradually decreases.?C?The MAO film almost has been stripped off,and the mass loss rate is comparable to the steady cavitation erosion period of the TiB₂/A201 composites.?4?With the formation of MAO film,the corrosion resistance of TiB₂/A201 composite to Cl^?has been greatly improved due to the effective inhibition of the anodic process.Among these films,the film prepared at10A/dm² is the most compact and has the best corrosion resistance.The I_corr has been reduced by 135 times compared to the TiB₂/A201composites.