No abstract

No abstract

No abstract

The interest of using magnesium alloys in several domains especially in automotive industry is growing. The most used commercial magnesium alloy is AZ91D because of its good mechanical properties and better anticorrosion performance as compared to others. [1][2][3][4][5][6][7] However, the creep resistance of AZ91D is low. This disadvantage limits its application in automobile motors where the temperature is higher. Some new magnesium alloys such as AJ52x and AJ62x were developed for this concern.[8] Recently, General Motors developed an Mg-Al-Ca-Sr alloy (AXJ530) aimed at the use for automobile engine which is very promising to improve the creep resistance. The purpose of this work is to examine the corrosion property of the skin and bulk of die cast and thixocast AXJ530 Mg alloy in 0.05 M sodium chloride solution at 25°C by electrochemical impedance spectroscopy method.Compared to die casting, thixocasting process induces strong modifications in the microstructure of AXJ530 alloy in terms of distribution, composition and volume fraction of the constituent phases. These modifications lead to reduced porosity levels, but also improved strength and corrosion performance. [2,3] Electrochemical impedance spectroscopy (EIS) is a powerful tool to study corrosion kinetics and corrosion mechanisms. Song et al. used EIS to investigate the relation between the microstructure and the corrosion resistance of magnesium and magnesium alloys. [4][5][6][7] They found that the corrosion resistance of the skin of die cast AZ91D alloy is significantly better (by nearly a factor of 10) comparatively to the bulk. This improvement was attributed to a higher b phase fraction, a more continuous b phase around finer a grains and a lower porosity. However, they defined the 0.5 mm depth section from the cast surface as "skin"; actually, this could be considered as a bulk under the real skin. Mathieu et al. studied the corrosion behavior of thixocast AZ91D alloy using EIS and other methods. [3] They indicated that the thixocast alloy had a corrosion rate at least 35 % below that of the die cast alloy. In that case, the better corrosion resistance was attributed mainly to the higher aluminum concentration in the primary a phase and could not be due to b phase acting as a barrier, since this phase was present discontinuously at grain boundaries. Recently, Blawert et al. have studied the corrosion properties of two die cast Mg-Zn-RE alloys and found that the bulk corrosion properties were much better than the skin properties. [9] These authors have also examined the corrosion behavior of the skin and bulk of AZ91 alloy and concluded that the skin is not necessarily better than the bulk. [10][11][12] The present study is aimed at comparing the corrosion behavior of the skins and the bulks of die cast and thixocast AXJ530 alloy. Results and DiscussionsDie Cast AXJ530 (AXJ530-DC) Skin of AXJ530-DC Samples: In this work, when the working electrode was introduced into the cell, the measurement of electrochemical impedance at open circuit potential...

No abstract