Study On The Fatigue Performance Of Adhesive-bonded AZ31 Magnesium Alloy Joint

With the development of light weight motor vehicle, the amount of the magnesium alloy used in the motor vehicle increases gradually. It is very difficult to connect magnesium alloy by means of traditional welding technique because of the higher chemical activity of magnesium alloy. Adhesive bonding may be an alternative joining technique for connecting magnesium alloy. With the financial support of Zhengzhou university and General motors corporation united fund project "Joining of dissimilar materials with crash-toughened adhesives", the author of this paper systemically studied the fatigue performances of the adhesive-bonded AZ31 magnesium alloy joint. The main researching works are as fellows.1 The effects of the surface pretreatment on the mechanical performances of the adhesive-bonded magnesium alloy joints were investigated. The results show that the shear strengths of the adhesive-bonded joints pretreated with abrading or with phosphate coating are improved. But the fatigue performance of the adhesive-bonded joint pretreated with abrading is worse than that of the adhesive-bonded joint pretreated with degreasing when the load is lower. The fatigue performance of the adhesive-bonded joint pretreated with phosphate coating is better than that of adhesive-bonded joints pretreated with degreasing or with abrading. It can be seen that the shear properties of the adhesive-bonded magnesium alloy joints cannot fully reflect their fatigue performances.2 The effects of the environmental exposure at the condition of 40℃,96%RH after curing process on the mechanical performances of the adhesive-bonded AZ31 magnesium alloy joints pretreated with phosphate coating or with abrading were studied. The results indicate that the shear strengths and fatigue performances of adhesive-bonded joints after the environmental exposure for 10 days all decrease significantly. The fatigue performance of the adhesive-bonded joint pretreated with phosphate coating is better than that of the adhesive-bonded joint pretreated with abrading. When the load level is lower, the fatigue life of the adhesive-bonded joints pretreated with phosphate coating with the environmental exposure are longer than that of the adhesive-bonded joints pretreated with abrading without the environmental exposure. It can be seen from these results that the fatigue performances of the adhesive-bonded joints depend on not only the static shear strength, but also the base surface structure and properties.3 The effects of the environmental exposure at the condition of 40℃,96%RH before curing process on the mechanical performances of the adhesive-bonded AZ31 magnesium alloy joints pretreated with phosphate coating or with abrasion were studied. The result demonstrates that the environmental exposure for 7 hours before curing process has no obvious effect on the shear strength and fatigue performance of the adhesive-bonded joint.4 The effects of the pretreatment of the surface of the magnesium alloy on the fatigue crack growth behavior in the adhesive-bonded joints were investigated. The results indicate that the three point bend specimen can be used to study the fatigue crack growth property of adhesive-bonded joint. The fatigue crack growth behavior of the adhesive-bonded joint pretreated with abrasion is similar to that of the adhesive-bonded joint pretreated with sodium silicate-pyrophosphate solution.5 The effects of the environmental exposure on fatigue crack growth in the adhesive-bonded joint were investigated. The results show that the resistance to fatigue crack growth of the adhesive-bonded joint decreases significantly if the cured adhesive-bonded joints are exposed at the environmental condition of high temperature and humidity for several days. And, if the adhesive-bonded joints are exposed at the environment condition of high temperature and humidity before curing for several hours, the reduction of the resistance to fatigue crack growth of the joints is not very obvious.