In-situ Investigation Of The Dynamic Growth Of Pitting Corrosion Of Mg Alloys

Magnesium alloys have many excellent properties,which have been widely used in automobile industry,aerospace,biomechanics and other fields.However,the development of magnesium alloys is severely restricted due to it's poor corrosion resistance.Pitting corrosion is a important local corrosion form,which is very destructive and has hidden danger.The corrosion resistance of magnesium alloys will be greatly improved until the corrosion mechanism of magnesium alloy corrosion is understood very wellBoth GW93 and G04 magnesium alloy as the research object,using the Scanning Electron Microscope,Scanning Vibrating Electrode Technique,X-ray Photoelectron Spectroscopy,electrochemical tests and immersion experiment methods to determine the controlling factors of the corrosion development of magnesium alloys,the micro structure of different magnesium allo ys of the second phase how to influence the development of pitting corrosion,the effects of corrosion medium on pitting development were clarified by experiments.The experiments also clarified the reasons for the development of the corrosion.The in-situ observation by SVET confirms that the corrosion microcells change dynamically with the growth of pitting corrosion.Serious pitting corrosion is observed at the applied anode potentials while corrosion is not observed at the applied cathode potentials.The results indicate that the propagation of pitting corrosion is under anodic control.The effect of the second phase with different chemical composition,size and distribution on the pitting process of magnesium alloy is studied.The results show that the pitting corrosion will arise from the second phase of magnesium alloy.The development of pitting corrosion of magnesium alloys will be accelerated when the larger the size of the second phase and the more the second phase.The result also indicates that the germination and development of pitting corrosion are associated with the second phase of magnesium alloys.Compared the surface films of Mg alloys formed in NaCl and Na2SO4 and NaNO3 solutions,the film in NaCl is the thinnest,in Na2SO4 solution is relatively thick,and that in NaNO3 is the thickest.The surface film in NaCl solution is relatively loose,the Cl-preferential adsorption in the incomplete place of the surface film,which leads to the initiation of corrosion.The corrosion will develop along the high concentration of Cl-.