Study Of Partial Ablation Phenomena During Micro-arc Oxidation On Magnesium Alloy And Solving Method

Micro arc oxidation is a new material surface treatment technology,which developed on the basis of anodic oxidation.The principle of this new technology is adjusting the electricity parameter and electrolyte parameter for producing a discharge in the anode surface.This process will make a ceramic film.Persistent gas combustion in the course of Micro-arc Oxidation on magnesium caused workpiece lapse or scraps. The workpiece will discard as useless when this phenomena was happens.This was became the key problem in Magnesium alloy application.In this paper,through a great deal of experiments that magnesium alloy AZ91D being treated by micro arc oxidation in different electrolytes and electricity parameter. Observed the partial ablation phenomena in the process of this experimentation,and then optimize the electricity parameter and electrolyte parameter.Study showed that: Na₂SiO₃13g/L,KF12g/L,NaOH4g/L,pulse frequency 700Hz,and duty cycle 20%are the best parameters for controlling partial ablation.To settle this problem,we studied the arc control method during the Micro-arc Oxidation.There are two flameout modes, one named nature,the other is force flameout.Nature flameout and force flameout are characterized by arc shape,physical model,circuit,pulse waveform.The results showed that the film is coarseness,such as holes and canyons under nature flameout while the film is smooth,and oxide-film combined tightly with ceramic film.Force flameout has the advantage of controlling film destroyed compared with nature flameout.Study shows that:Micro-arc oxidation process can be divided into three stages, namely:anodic oxidation stage,the micro-arc oxidation stage and continuous arc stage. Ceramic layer components by Mg,MgO,MgAl₂O₄,Mg₂SiO₄ phase,the key elements is the O,Mg,Al,Si,F.The process of micro-arc oxidation on magnesium alloy essentially is statistical results for a single micro-discharge.The surface of magnesium alloy grow the layer of insulating film thin and transparent immediately after electricity,when the a weak bubble department has been in strong breakdown voltage, this part of gas was dissociation use energy of electron impact when breakdown,form of discharge channels,generated plasma,there is the phenomenon of gas discharge, and then a series of high-temperature reaction,generate to ceramic film.For the purpose of researching which Power Source Form Micro-arc Oxidation Formed on Mg Alloys need,we took experiments of magnesium alloy with three kinds of power for micro-arc oxidation at DC pulse,AC pulse and with discharge circuit.The study founded that the form of DC pulse will cause continual arc and loss by burning test specimen;AC pulse can inhibit the producing of continual arc because of the existence of negative pulse,but a large amount of fixtures adhere to the film surface which caused to caddish of film because of the existence of negative voltage.The design principle of power form with discharge circle is adding a discharge circuit at both ends of load after Positive pulse,took experiments for micro-arc oxidation of this power can inhibit the producing of continual arc,and film growth rate is higher than in AC pulse power form.So magnesium alloy micro-arc needs the power form with discharge circuit.