Study On Effect Of Corrosion On The Strength Of AZ91 Magnesium Alloys

The worldwide energy crisis and environmental protection win more and more attention, which lead to the development of automobile industry towards the light weight direction. Thereby magnesium alloys are getting more and more popular due to its specific strength and light density. However, their common flaws, such as, lower strength and bad corrosion resistance, which significantly restrict their development and application in practice. And thus these subjects related to corrosion and strength of the magnesium alloys have become the popular ones to material researchers. Actually, corrosion problem is inevitable when magnesium alloys are in use, which causes the drop of materials'strength continuously. In fact, this phenomenon has developed into a potential safe problem to the magnesium alloy components.At present, AZ series magnesium alloys have already been turned into real productions and acquired extensively commercial operations. Besides, AZ91 magnesium alloys acquired a remarkable reputation for its excellent overall properties. Therefore, the cast AZ91 magnesium alloy was employed as the testing material in this paper and with regarding to the functional mode and working environment, the pre-corrosion method was adopted as the researching method. The tensile test bars were immersed into the 3.5%NaCl aqueous solution (pH=7.0) and then the tensile test was proceeding after the tensile test bars were taken out from the corrosion medium. As a result, the developing regulation of the residual strength (σr) and its influencing factors were all obtained under these circumstances. The rare earth Y was introduced to modify the AZ91 magnesium alloy in order to suppress the drop of the residual strength. Simultaneously, the effect of the rare earth Y on the residual strength of magnesium alloy was investigated. Potentiodynamic polarization curve, open circuit potential tracing, the gathering of hydrogen gas, scanning electronic microscopy, optical microscopy, XRD and statistical analysis for corrosion pits were accepted as the primary researching means for the analysis of the residual strength of AZ91 and the Y modified AZ91 magnesium alloy. It reveals that the addition of the rare earth Y could effectively suppress the cathodic hydrogen generation reaction and at same time restricted the anodic dissolution to some extent. Therefore, the corrosion resistance of the AZ91 magnesium alloy is improved and simultaneously ameliorates its residual strength. In addition, the network distribution ofβphase at the grain boundary of the primaryαphase can effectively block the development of corrosion pit into the alloy matrix, which indicates that the networkβphase is beneficial to suppress the drop of the corrosion residual strength. The addition of Y significantly refined theβphase and improved the strength and plastic property of magnetism alloy. To some extent, this result is not good information for the control of the development of the corrosion pits. Generally, the addition of Y is beneficial to the improvement of the overall properties.The addition of Y generally improved the corrosion resistance and enhanced the original strength of the AZ91 magnesium alloy. And therefore the effect of Y is positive to the AZ91 magnesium alloy.With respect to the corrosive characteristic of the AZ91 magnesium alloy(Judging from the corrosion morphology) in the presence of , the corrosion residual strength of the AZ91 magnetism alloy mainly depends on the deepness of the corrosion pit. On the one hand, the initiation and development of the corrosion pits remarkable varies on the surface configuration of the alloy and thus causes the stress concentration; on the other hand, the development of the corrosion pits reduces the effective loaded area, which leads to the drop of the residual strength. The residual strength of both AZ91 and Y modified AZ91magnesium alloys was linearly depends on the increasing of the corrosion pit dimension. In 3.5%NaCl aqueous solution, the residual strength of both AZ91 and Y modified AZ91 magnesium alloys exponentially decayed with time. Cl- According to influencing factors of the residual strength, the evaluation criterion and related methods were promoted in this paper, i.e. max( corrosion pit dimension).