Evaluating The effect of the pin's length to the strength of double sides Friction Stir Welded aluminum

Based on previous research, it is believed that the use of double side friction stir welding can improve the obtained joint. It is hoped that a longer pin could broaden the strain hardened area (especially the interference zone) which in turn could produce stronger joints. From tensile test data it can be seen that the tensile strength it is indeed increased by the length of the pin. The maximum tensile strength of 183 MPa was acquired with a pin's length of 6.5 millimeter, which corresponds to a 75% joint efficiency, whilst the lowest efficiency, 42 MPa, was found when the 2.5-millimeter pin was used. The hardness test confirmed the existence of the strain hardening phenomenon, which was shown by the presence of harder materials at interference zone. Other supporting evidence is the micro structure photography. Photos show that the interference zone not only exhibits strain hardening, but also yields a finer dispersed micro structure that provides a stronger joint. A simple Finite Element Simulation was performed to complete and deepen the analysis.