Research On Friction Stir Welding Process Of LY12 Aluminum Alloy

To meet the high demands on the body structure such as high reliability, light weight, long life and low cost, the high strength aluminum alloy LY12 has been widely used to form integral structure components in general aviation aircraft industries. However, the welding defects like welding porosity and hot crack are caused by arc welding, which can be avoided effectively by friction stir welding(FSW).As a new solid welding method, its research in the general aviation is still at initial stage, further study of FSW process on LY12 aluminum alloy sheets has great significance on general aviation development.LY12 aluminum alloy sheets with thickness in 2mm and 3mm were welded by FSW in this paper. The metallographic test, room temperature tensile test and micro-hardness test were conducted to study the microstructure and mechanical properties of weld joints.It was found that welding joint could be divided into four different areas: nugget zone, shoulder-affected zone, thermal mechanically affected zone and heat-affected zone. Nugget zone and shoulder affected zone are fine equiaxed recrystallized grains and heat affected zone is typically elongated deformation microstructure. With the increase of spindle speed, nugget zone grain growth, the precipitation phase was re-dissolving and refining. The thermal mechanically affected zone of forward side was narrow. The grain twist increasing and deformation texture characteristics gradually clear. The hardness distribution of weld joints showed "W" shaped. The hardness of heat affected zone hardness was minimum, which might be caused by the more deformation defects and larger internal stress.With the increase of spindle speed, the tensile strength of weld joints increased and decreased afterwards. The changing of welding speed has little effect on mechanical properties of weld joints. For 3mm thickness LY12 aluminum alloy sheet, when spindle speed is 500-1100 rpm, welding speed is 160-240mm/min, the good appearance can be obtained with free defects inside the weld. When spindle speed is 800 rpm, welding speed is 160mm/min, the maximum tensile strength of the weld is 347 MPa. For 2mm thickness LY12 aluminum alloy sheet, when spindle speed is 300-1200 rpm, welding speed is 120-200mm/min, the weld surface was smooth and no internal defect was found. When spindle speed is 600 rpm, welding speed is 200mm/min, the maximum tensile strength of the weld was 276 MPa.