Investigation On The Correlation Between Welding Technology And Stress Corrosion Ofaluminum-Copper Alloy Welding Joint

Due to the effect of the welding heat cycle, heat affected zone of the welding joint can be soften, that is, the decomposition of precipitates precipitation will inevitably be caused by the averaging factor during the aluminum alloy used for welding structure. The strength properties of joints will be depressed by the phenomenon. At the same time because of the inhomogeneity of the tissue and the poor copper area, the joints will be easy to produce the electrochemical corrosion damage and the sensitivity of the stress corrosion cracking(SCC) of joints will significantly increase. This engineering problem has been unresolved for a long time. Therefore, researching on the corrosion failure characteristic of aluminum alloy welding joint, and to analyze factors that lead to the corrosion failure has a very important engineering significance for improving the long-term performance of welding structures of significant space aluminum alloy.The samples of welding joints in this study are carried out for macro-mechanical tests,low strain rate tests, the sample joint microstructures and the fracture surface SEM images have been observed by utilizing the metallographic observation technologies. The mechanical property and stress corrosion resistant performance comparison to the welding joints have been carried out for the aluminum-copper alloy 2014 and 2219 under different welding conditions, that is, VP-TIG welding, high frequency (HF)-TIG hybrid welding, laser -TIG hybrid welding and laser HF-TIG hybrid welding, so that the relationship of the welding processes related to stress corrosion resistant capability could be obtained and realized, and with that to find an optimal welding method which will ensure high strength and resistance to stress corrosion of welding joints.The results showed that low power laser and high-frequency pulse energy can effectively reduce or even eliminate the porosity in the fusion zone of welding joints, and due to the strong stirring effect of high frequency pulse which can smash the growing dendrite and to prompt the formation of thin-grain belt in the fusion zone of joints. Compared with the VP-TIG welding,laser-TIG hybrid welding, HF-TIG hybrid welding and laser HF-TIG hybrid welding can significantly improve the welding speed, reduce the heat input, refine the weld microstructure and reduce the width of grain boundary eutectic, thereby can significantly improve the mechanical property and the resistance to stress corrosion of joints. The resistances to stress corrosion of five kinds of welding joints of aluminum alloy 2219 are quite different, in which the joint through the high power laser-TIG hybrid welding has the lowest elongation and highest cracking sensitivity, and the average fracture time of joints through the laser HF-TIG hybrid welding is significantly longer than that through the VP-TIG welding, which is about 94% of that for 2219 base material and the resistance to stress corrosion is the best among other welding joints. However, this index may be up to 60% of that for the base material as for five kinds of welding joints of 2014. The effect of high frequence or laser hybrid is not significant under the same welding conditions for welding joints of 2014. Although the welding joint grain structures are refined to some certain extent, the grain structures in the poor copper area are not distributed more well in comparison with those for joints of 2219, and the cracking sensitivity may be intensified. Therefore, the further research and development on the hybrid welding processes suitable for aluminum alloy 2014 should be carried out specially.