Influence Of Alloying Elements On The Anticorrosion Performance Of Magnesium Alloys

Magnesium alloys are widely used in automobile, aerospace,3C (Computer,Communication and Consumer Electronics) products, medicine and other fields owingto their advantages of light quality, high specific strength and stiffness, low price,excellent recyclability and so on. However, the high chemical and electrochemicalactivity greatly hinder magnesium alloys to show their performance advantages. Addingalloying elements is one of methods to get high performance magnesium alloys, it notonly can improve the mechanical properties of magnesium alloys, but also can improveits corrosion resistance. So the effects of alloying elements on the anticorrosionperformance of magnesium alloys were mainly studied in this paper, it would be havecertain significance in promoting the widely application of magnesium alloys.The influence of different alloying elements on the anticorrosion performance ofMg-Al based magnesium alloys were studied by free corrosion potential-time curves,polarization curves and electrochemical impedance spectroscopy, and then the optimumcontents of alloying elements to improve the anticorrosion performance were obtained.At the same time, the microscopic morphology and composition of magnesium alloyswere characterized by optical microscope, scanning electron microscopy, energydispersive spectroscopy and so on, and the composition of corrosive products werestudied by X-ray photoelectron spectroscopy. The results show that:By adding different contents (0,0.3,0.6,0.9,1.2wt.%) Sr element in AZ31magnesium alloy, the anticorrosion performance of AZ31-0.9Sr magnesium alloyimproves by65.94%than AZ31magnesium alloy and this indicates that the addition of0.9wt.%Sr is the best to improve the anticorrosion performance of AZ31magnesiumalloy. The results of microstructure and corrosive products show that the number ofmicro-galvanic cells is decreased, because the microstructure of AZ31-0.9Sr magnesiumalloy is more homogeneous due to the refinement of the grain size of AZ31-0.9Srmagnesium alloy, the proper formation of less cathodic Sr-containing compounds andthe increase of the precipitates as well as their more continuous distribution along thegrain boundaries. All these aspects are benificial for the improvement of theanticorrosion performance of AZ31-0.9Sr magnesium alloy. Moreover, thedisappearance of the cracks and the stability of the corrosive products film ofAZ31-0.9Sr magnesium alloy are also responsible for its lowest corrosion rate. By adding different contents (0.5,1.0,1.5,2.0wt.%) Y in AZ31magnesium alloyafter adding0.5wt.%Sr element, AZ31-0.5Sr-1.5Y magnesium alloy has the bestanticorrosion performance and its corrosion rate decreases by63.02%than AZ31magnesium alloy. This is concerned with the decrease of the number of micro-galvaniccells because the microstructure is more homogeneous owing to the grains of AZ31magnesium alloy is refined by adding0.5Sr+1.5Y and the proper formation ofSr-containing and Y-containing compounds. At the same time, it is related to theimprovement of the stability of the the corrosive products film. However, addingexcessive Y element such as2.0wt.%Y is not beneficial to the anticorrosionperformance because excessive Y can cause serious composition segregation and hencecause the enrichment of less cathodic phase, form the strong cathodic phase, and thenincrease the cathode polarization behavior, cause increase in local micro-galvaniccorrosion current.The addition of different contents (1.0,2.0wt.%) rare earth Y in Mg-5Al-1Sr-2Camagnesium alloy made the corrosion current density one order of magnitude less thanMg-5Al-1Sr-2Ca magnesium alloy, improve its anticorrosion performance. Thisimprovement may be attributed to the decrease of the number of micro-galvanic cellsowing to the refinement of microstructure, the formation of less cathodic phase Al2Yand more stable phase Al2Ca. In addition, Y only dissolved in the Mg matrix ofMg-5Al-1Sr-2Ca-1Y magnesium alloy and this can increase the protective nature of thesurface film, so the anticorrosion performance of Mg-5Al-1Sr-2Ca-1Y magnesium alloyis the best.