Process Study Of Friction Stir Spot Welding On Aviation High Strength Aluminum Alloy

Friction stir spot welding(FSSW)is a new type of solid-state spot connection technology.Basing on the spot welding project of Avic Beijing institute of manufacturing engineering,the research welded 2.2 mm of 7b04 aluminum alloy plates with backfill type friction stir spot welding technology.In order to avoid defects,we need to choose a reasonable process parameters.In improper process parameters,backfill type friction stir spot welding joints may have surface defects: surface sticking of material,surface scratches,material lacking in center and edge,inclusion and flash,etc.Internal defects include hook defects and connection ligament defects.According to the X-ray image,other defects can be observed,such as edge groove defect.Under X-ray detection,joint regional variation in thickness is analyzed.Backfill type friction stir spot welding joint zone can be divided into the needle area and the sleeve area,by analyzing the microstructure,we can find the mechanism of the joint formation.The regional microstructures have big differences.Speed and depth has the greatest influence to microstructure.Joint hardness distribution shows the "W" shape,welding nuclear area has highest hardness,heat affected zone and thermal affected zone adjacent to the lowest hardness.A higher mechanical properties of joint is the basis of the friction stir spot welding application.Through the two groups of orthogonal experiment under different process parameters,we can obtain the excellent mechanical properties of friction stir spot welding joint,and analyze the fracture morphology.The fracture form of joints include interface separation,stir zone divorced and edge tear.