Study On The Laser-MIG Hybrid Welding Of7075-T6Aluminium Alloy

7075aluminum alloy is a wrought alloy, which strength is better thanmild steel, is one of the most powerful commercial aluminium alloy. Due to itssuperior performance, which are widely used in aerospace, transportation andother industries. However,7075aluminum alloy’s fatal drawback is that thepoor welding performance, for a long time it is considered can’t be welded.Thus, when7075aluminium was used for structure meterial, the riveting wasalways used to connect. But not only the riveting strength is lower thanwelded joint, but the entire structure’s weight is also greater than welding.This way to connect7075aluminium is a waste of material, and the the overallrigidity of the structure is weakened. High energy density is a characteristic oflaser beam, which making it ideally suited for the welding of7075aluminum alloy. But laser beam weld7075aluminium alloy may cause somewelding defects, like gas pore, crack. And the utilization ratio of laser beamwelding is lower. The laser-arc heat source can greatly improve laser weldingprocess characteristics and its bridging. This method not only can improve thewelding efficiency, but also expand the process margin. In this paper, thelaser-MIG hybrid welding process performance and joint area micro-mesoexperimental research was carried out, the conclusions are educed.The laser-MIG heat source was connected in paraxial way. The shape ofjoints appearance of the different process parameters was observed, andcompared with the single laser welding joints. The results show that the jointcan be gained with neat appearance and without undercut, cracks,discontinuities and other macroscopic defects in the reasonable processparameters.The mechanical properties testing shows that the tensile strength ofhybrid welding is279Mpa,53%of the parent material strength (524MPa). Themetallographic and hardness analys showed that the major softening phase isflakes organizations, such organizations gathered in the center of the joints,which make the middle of the joint to be the weakest zone.Synchrotron radiation X-ray fluorescence CT observation showed thatthe big size gas pore gathering in the middle of the joints, and smaller size onboth side of joints. There exist large number of small micro-voids on fusion zone, these micro-voids can lead to decline of fatige performance.Compared the EDS line scan results of laser-MIG hybrid welding andlaser beam welding, it can be found that the copper and zinc content in hybridwelding joints is less than laser beam welding, this is the main reason whichcaused hybrid joints’ low hardness. After analysed the synchrotron radiationhard X-ray scanning element distribution and the cloud images of hardness, itcan be found that the hardness distribution is accord with copperdistribution,so, a conclusion can be draw that copper is one of the mainelements which affect the joint hardness.