Study On Microstructure And Mechanical Property Of A7N01 Joint In Laser-MIG Hybird Welding

Lightweight is the main measure of the current car, train, aerospace and other industries to achieve energy conservation. The high strength aluminum alloys which are corrosion resistance and high strength are more and more widely used. Laser-MIG hybrid welding technology integrates the advantages of both heat and has a higher welding efficiency and stronger ability to adapt to the current research. But studies have shown that the presence of welding poor, pores, cracks and other defects in aluminum alloys welding joint. Therefore, the paper carried out a 4mm thick aluminum A7N01 using laser hybrid welding-MIG test to focus on its welding characteristics, porosity distribution, joint microstructure evolution mechanisms and mechanics of the joint, designed to achieve complex welding of high strength aluminum alloy lay the foundation for engineering applications.The results show that: the main parameters affecting the shape of the laser weld power is welding current and welding speed, when the welding speed is constant, the weld penetration depth depends on the laser power, weld width depends on the welding current. By optimizing the process parameters to obtain a good surface formed as follows: welding speed of 4m / min, the defocus amount is-2mm, current is 140 A, the laser power of 3.5kW, light wire spacing is 2mm. The central area of the weld formed dendritic structure clear, while the weld fusion zone formed a columnar grain structure to the growth direction of the weld. Weld strengthening elements Zn evaporation leads to significant reduction of strengthening phase particles, which is one of the main causes softening of aluminum composite welding head.Based on the measured construct synchrotron radiation X-ray imaging technology and Amira software the joint internal porosity were analyzed. The results show that the volume fraction of porosity in the weld of 0.57%, the maximum area fraction of 3.56%. Hydrogen hole in the upper region of the weld centers dispersed, nearly spherical, the size is about 0. 1-79?m; mini-pores are densely distributed throughout the weld area, on both sides of the weld center presents approximately symmetrical distribution; craft pores exist in the lower seam, irregular spatial morphology, size is about 110 ~ 120?m.The average hardness of the weld zone is 76 HV which is lower than the base metal hardness, about 77.56% of the base material. Joint fracture occurs in the weld center position, and the tensile strength is 268 MPa, reached 76.6% of the base material. The existence of a large number of porosities reduces the bearing area of welded structures. Welded joint fatigue crack initiation and synchronous development with multiple source, the characteristics of the fatigue crack source is mainly for the joint of welding defects such as slag inclusion, porosity, crack, crack extension area clearly secondary crack characteristics and fatigue striations. Instant-off area is similar to the static load fracture toughness fracture.