Friction stir lap joining aluminum and magnesium alloys

Al–Si and Mg–Al–Zn alloys were lap joined using friction stir welding during which the probe of a tool did not contact the surface of the lower Mg–Al–Zn alloy sheet. Micro X-ray diffraction was used to analyze phase transition in the joint. A conversion zone exists between the stir zone and the lower sheet metal which contained intermetallic compounds Al12Mg17, Al3Mg2 and Mg2Si. Using a lower welding speed resulted in no visible welding cracks and improved the joint strength.