Residual Stresses Measurement And Numerical Simulation For Friction Stir Welding Of Aluminum Alloy

The invention of friction stir welding(FSW) broadens the application of aluminum alloy further. Because the FSW on Al has the advantage of low-distortion, little pollution and good mechanical performance of joint, it is widely used in aviation, aerospace, navigation, railway vehicles and automobile making industry and so on, and remarkable achievement is made. Generally speaking, when FSW is carried out on the medium plate, double sides friction stir welding is more cost-effective than the single side friction stir welding. Therefore, the study of double sides FSW is of great practical significance.Although the residual stress of wielding joint of aluminum alloy of FSW is much smaller than that of fusion welding, residual stress existing has great iMPact on utility-performance of joint. Hence the study of residual stress of welding joint is very necessary and meaningful.5mm thickness of 5A15 aluminum alloy plate was selected as the experimental object, respectively undergoing single side and two kinds of double sides FSW under the optimal parameters. Samples were taken from the three kinds of welding plates respectively to analyze the micro-hardness of three layers. It is found that the shapes of the micro-hardness distributions of the FSW joints by the three ways are like “W” vertical to the welding direction. Although the micro-hardness of three layers is slightly different on the whole, not discrete; the micro-hardness of different regions are different, but they can transition smoothly.Hole-drilling method was used to measure the residual stress of the plates that welded by the three kinds of welding methods. The result shows that the longitudinal residual stress is much larger than the transverse residual stress of the three groups of test plates. The maximum residual stress that measured is 130.6MPa, 41.5% of the yielding strength of parent metal, which is lower than the residual stress of fusion welding of aluminum alloy.At the same time, the single side and double sides FSW three-dimensional numerical analysis models were established respectively. Firstly, the two kinds of FSW temperature field were simulated, and as one of the boundary conditions they were coupled in the stress analysis model. Meanwhile considering the heat input and the cooling condition in the models, temperature field contours, temperature cycle cycles and the residual stress contours that obtained finally are well in response to the practical laws.