Estimation of Material Flow in Stir Zone during Friction Stir Welding by Distribution Measurement of Si Particles

The size. aspect ratio and direction angle of the Si particles in the stir zone were investigated for the ADC12 FSW joints to analyze the material flow in the stir zone by quantification of three elements (size. aspect ratio and direction) under various welding conditions. The number of finer Si particles increases with the increasing welding speed, whereas, the change in the number of finer Si particles is not simple when the rotation speed is varied. The stirring action during the FSW is appraised by the size of the Si particles. The aspect ratio of the particles increases with the increasing size of the particles. The welding conditions also influence the direction angle of the Si particles. Under the proper conditions, the flow directions of the Si particles in the top and bottom are horizontally aligned, while they are longitudinally aligned on the retreating side and advancing side. However, under insufficient heat input conditions, the material flow becomes random in the bottom and retreating side regions. Under abnormal stirring conditions, on the other hand, it is random on the advancing side and top regions, even though a defect forms on the advancing side in both cases. This kind of identification of the material flow might be very useful to determine the optimal welding conditions by avoiding,my defect formation.