The Fatigue Performance Of Riveted And Rivet-bonded Joints For Magnesium Alloys

The environmental protection and resources shortage result in the increase of the energy price. The energy saving is becoming a more and more important issue. Reducing the weights of vehicles is an effective way to decrease the energy consuming. If magnesium alloys are used to manufacture some parts of vehicle body, the weight of the vehicle body can be decreased correspondingly, so achieving the purpose of energy saving, environmental protection and security. However, the traditional welding technique is not suitable for connecting magnesium alloys because of its higher conductivity and easily forming oxide layer while welding. The author of this paper utilized two techniques, self-piercing riveting (SPR) and self-piercing riveting-bonding (SPR-B), to connect AZ31 magnesium alloy sheet experimentally, and investigated the mechanical performances of the joints systemically. The main researching works and results are as follows.1.The AZ31 magnesium alloy sheets were riveted by using the SPR technique experimentally. The riveting conditions of the sheets and the shear and fatigue performances of the riveting joints were investigated. The results show that the SPR technique can be used to connect magnesium alloy sheets, but the temperature of the sheets must be kept at about 180℃during riveting. The riveting joints have the excellent shear strength and fatigue performances, which are superior to the performances of the magnesium alloy joints connected by using resistance spot weld (RSW) technique.2.The SPR-B technique is used to join AZ31 magnesium alloy sheets, and the shear and fatigue performances of the joints with different surface treatments were investigated. The results documented that the addition of adhesive obviously increases the shear strength and fatigue performance of the joints. The higher surface energy after the surface treatment is, the better the shear and fatigue performances are.3.In order to study the shear and fatigue performances of the SPR and SPR-B joints for different materials, AZ31 magnesium alloy and DP600 steel sheets were joined by means of the SPR and SPR-B techniques. The results indicate that the SPR and SPR-B are the ideal joining techniques for connecting different materials. The adhesive increases the fatigue strength of the joints because of the higher surface energy of DP600 steel.4.AZ31 magnesium alloy sheets were joined by the SPR with the homemade flat die, and he shear strength and fatigue performance of the joint were studied. The results show that the SPR with the flat die can improve the shear strength and fatigue performance, and the flat die is yet a multi-purpose die.5.AZ31 magnesium alloy sheets were joined by using the SPR with the hollow rivets that had been injected with adhesive. The shear and fatigue performance of the joint were investigated. The results show that the adhesive injected reduces the friction between rivet and the sheet, so decreasing the possibility of the fatigue crack initiation and the electric chemical corrosion between the rivet and the sheet.