Study On The Elimination Of Welding Residual Stress Of Al-Zn-Mg Alloy By Thermal-Vibration Stress Relief Method

The 7N01 aluminum alloy used in high-speed train is one of Al-Zn-Mg high strength aluminum alloy and it will generate large welding residual stress after welding.The existence of residual stress will lead adverse affect to the performance of the structure.Vibration stress relief(VSR)is a new method to eliminate residual stress,which is simple,portable,energy-saving,environment-friendly,efficient and safe.It has been widely used in ferrous metal to eliminate welding residual stress.For high-strength aluminum alloys,because the welding residual stress is far from the yield strength of the material,the conventional vibration stress relief treatment have no obvious effect on eliminating welding residual stress.In this paper,combined with the study of vibration stress relief of 7N01 aluminum alloy,thermal-vibration stress relief(TVSR)treatment is proposed.By combining the theoretical analysis and experimental research,the effects of temperature of thermal-vibration stress relief on the elimination of welding residual stress and the effect of thermal-vibration stress relief on the mechanical properties and microstructure of the material were studied.Based on the principle of vibration stress relief and the aging process of aluminum alloy,a thermal-vibration stress relief platform was built.First,the mechanism of VSR was analyzed from the macroscopic and microscopic perspectives,and a VSR platform that satisfies the experimental requirements was set up.Then three kinds of heating methods,including welding residual heat,flame and heating belt,were explored.Finally,a ceramic heating belt system with temperature feedback was selected.Combining theoretical analysis and experimental investigation,the selection principle of VSR parameters is proposed.The influence of temperature on the effect of TVSR to eliminate residual stress was studied.First,with the increase of temperature,the strength of the material decreased,and it has decreased significantly from 100 to 200 °C.Then the aging precipitation of 7N01 aluminum alloy was studied.The precipitation temperature of 7N01 aluminum alloy aging strengthening phase was in the range of 120-170 °C.The welding joints were subjected to comparative experiments at different temperatures.After Thermal vibration stress relief treatment at 25 °C(room temperature),100 °C,150 °C,and 200 °C,the peak residual stress decreased by 38.3%,50.7%,60.0%,and 74.0%,respectively.With increasing temperature in the range of 100-200 °C,the effect of eliminating residual stress was better.Thermal-vibration stress relief treatment of 7N01 aluminum alloy large welded structural parts was conducted to study the effects of thermal-vibration stress relief on the properties and microstructure of the materials.After thermal-vibration stress relief treatment,the tensile strength of the joints is improved,the hardness and fatigue properties remain basically unchanged,and the bending and stress corrosion resistance of the materials are still good.The microstructure of the welded joints is clearly refined,the micro dislocation density increases,the distribution is even,and a large number of dislocation tangles occur,which is consistent with the increase in the strength of the material.Finally,the TVSR treatment and VSR treatment were applied to the actual structure of the bolster.The peak residual stress after Thermal vibration stress relief treatment decreased by 50.3% on average,while the peak residual stress after vibration stress relief treatment decreased by 28.5% on average.The results show that the Thermal vibration stress relief is more significant than the vibration stress relief to eliminate the welding residual stress.The thermal-vibration stress relief technology put forward by this group is the development of thermal-vibration stress relief technology.It has important guiding value in practical engineering applications and has broad application prospects.