铝合金搅拌摩擦焊力的周期性波动特征与机制

Characteristic and Mechanism of Periodic Oscillation of Force in Friction Stir Welding of Aluminum Alloy

利用三分量力传感器测得了8mm厚5A06-H112铝合金搅拌摩擦焊过程中的轴向压力(F_(z))、前进阻力(F_(x))、侧向力(F_(y))信号,着重分析了力周期性波动的规律及其与焊接缺陷的关系。研究发现:在稳定焊接过程中,F_(x)和F_(y)均呈现了周期性波动,波动频率与搅拌头的旋转频率一致;F_(y)波形滞后于F_(x),相位差为π/2;F_(z)波动较小。F_(x)和F_(y)的均值随搅拌头转速的提高而降低,随焊接速度的增加而升高。在一定工艺参数范围内,焊接缺陷与F_(x)和F_(y)波动特征有良好的对应关系:当焊缝中无孔洞缺陷时,F_(x)与F_(y)值域无重叠且波形接近正弦波;当焊缝中存在孔洞缺陷时,F_(x)与F_(y)值域部分重叠且波形发生畸变。模拟分析表明,搅拌头偏心为0.01 mm时,F_(x)呈现周期性波动,搅拌头不存在偏心时,F_(x)未呈现周期性波动,因此认为搅拌头的偏心旋转是造成F_(x)呈周期性波动的主要原因,而且搅拌头偏心旋转导致了周围材料应力场和流场的周期性变化。随着搅拌头的持续旋转和进给,形成了周期性的焊缝内部组织和表面成形。

A three-component force sensor is used to measure the plunge force(F_(z)),traverse force(F_(x)),and lateral force(F_(y))of friction stir welding(FSW)of 8 mm thick 5A06-H112 aluminum alloy.The cause of the periodic oscillation of the force signals and its relationship with welding defects are analysed.Both F_(x)and F_(y)showed periodic oscillations,and the frequency is consistent with the rotation frequency of the tool.The waveform of F_(y)lags behind F_(x)and the phase difference isπ/2.The oscillation amplitude of F_(z)is small.The average values of F_(x)and F_(y)decrease with increasing the rotating speed of the FSW tool,and increases with increasing of the welding speed.When the defective-free joint is obtained,F_(x)and F_(y)have no overlap and the waveforms of F_(x)and F_(y)are both sinusoidal waves.F_(x)and F_(y)overlapped partially and the waveforms of F_(x)and F_(y)show distortion when the defective joint is obtained.The numerical simulation results show that F_(x)presents periodic oscillations with the eccentricity of the tool of 0.01 mm.Furthermore,F_(x)keeps constant when the tool has no eccentric motion.Therefore,the eccentric rotation of the tool is the main reason for the periodic oscillation of F_(x).In addition,the eccentric rotation of the tool causes the periodic variation of the stress and flow of the plasticized material around the tool.With continuous rotating and traversing of the tool,the weld has the periodic internal microstructure and surface morphology.