Simulation on friction stir welding 7055 aluminum alloy based on CEL model

Based on the coupled Eulerian-Lagrangian (CEL) finite element model, a thermal-mechanical coupling calculation model of friction stir welding 7055 aluminum alloy with high reliability and precision was established. The effects of welding process parameters on temperature, equivalent strain and porosity defects of 7055 welded parts were predicted and analyzed. The friction stir welding experiment was conducted to verify the accuracy of the CEL model. The predicted results showed that the temperature and equivalent strain were proportional to the rotation speed of the stirring head and inversely proportional to the welding speed. This was mainly related with the frictional heat generation and material flow between the shoulder and the aluminum alloy sheet, which resulted in changes in the welding temperature and the equivalent strain value. When the welding speed was in the range of 60 − 300 mm/min and the rotation speed was in the range of 300 − 1 200 r/min, the welding temperature was lower than the melting point of 7055 aluminum alloy. When the welding speed was reached to 300 mm/min, the welded joints were prone to form weld porosity defects due to the lower temperature and equivalent strain caused by insufficient heat generation. The friction stir welding experiment results indicated that when the welding speed was 180 mm/min and the rotation speed was 600 r/min, the friction stir welded joints of 7055 aluminum alloy had compact microstructure. The tensile strength and elongation was 489 MPa and 4.0% respectively at this condition. When the welding speed was reached to 300 mm/min, the tensile strength was 411 MPa and the elongation was only 1.0%. This was related with the poor join caused by insufficient heat. The experimental results were in accordance with the simulated results.