Study On The Corrosion And Mechanical Properties Of AM50Magnesium Alloy

Magnesium is the lightest structural metal with the high specific strength and specificstiffnes, which receives widespread attention. Magnesium alloy as a auto part, whichreducing vehicle weight will help to improve the fuel economy, energy efficient andenvironmentally friendly. However, poor corrosion resistance and low strength inpractical application are seriously restrict its development and lead to sec urity risks inuse.In order to improve the security of magnesium alloy in use, meanwhile, predict itslife, as-cast AM50magnesium alloy was adopted as the target alloy for the study, by heattreatment, rare earth elements(Gd, Er) modified and hot extrusion processing. Systematicstudy with different treatments of AM50magnesium alloy were carried out for corrosion,mechanical properties. Further more, on the basis of previous work,the formula, whichpredict the residual strength of AM50magnesium alloy was summed.The T4, T6heat treatment and rare earth element (Gd and Er)could effectivelyimprove the corrosion resistance and properties of AM50magnesium alloy. The tensileproperty improved by solid solution and aging strengthening. β-Mg17Al12solid solutionin α-Mg, improve the corrosion resistance of α-Mg by increasing the content of Al inα-Mg. Meanwhile, the reducing of the β-Mg17Al12phase reduced the number of galvaniccell. The addition of rare earth element Gd/Er significantly improves the mechanicalproperties of AM50magnesium alloy by solid solution, fine grain and dispersionstrengthening. The rare earth element can refine the microstructure of the matrix, cleanthe composition of the alloy, reducing the amount of β-Mg17Al12, thus effectivelyreducing the micro-galvanic effect in corrosion process and promotes the corrosionresistance of AM50magnesium alloy. In general, rare earth modification could suppressthe decay of corrosion residual strength of AM50magnesium alloy, which is an effectivemean for the protection of the dynamic mechanical properties. The best addition is1%Gd and0.5%Er. The tensile strength of hot extrusion alloys all increased to above300MPa. Further more, their toughness and deformation capacity both improved. And the micro structure of the alloy obviously refined compare to as-cast alloys. Meanwhile, the addition of rare earth element increase the Al2Gds and reduce the amount of β-Mg17Al12phase. The hot extrusion lead increasing of α-Mg and β-Mg17Al12, which deteriorated the corrosion resistance of the alloy by increasing the micro-galvanic couples. The fracture morphology analysis shows that the fracture mode of three hot extrusion treated alloy is mixed fracture, which include the characteristics of ductile fracture and brittle fracture. Therefore, the hot extrusion treated AM50Gd1magnesium alloy shows the best corrosion residual strength property.On the basis of previous work, through a lot of data from different processing, a mathematical model of corrosion residual strength for AM50magnesium alloy is established predict the service life in corrosive environments. As follows:The corrosion creep properties of AM50magnesium alloy under constant stress with different concentrations of NaCl aquous solution was carried out exploratory. The results show that the corrosion creep is consist of three stage:deceleration creep, constant speed creep and accelerated creep. The Tafel curve analysis showed that corrosion potential and current was affected by deformation. The corrosion creep susceptibility of AM50magnesium alloy under5%concentration range in NaCl solution increases with the concentration of Cl-anion. From the fracture morphorlogy analysis, the fracture mode of corrosion creep in NaCl is brittle fracture, there were other cracks besides the main crack.