Friction stir method and a pair of workpieces joined by such method

A method for joining a pair of workpieces, the steps of the method comprising:

• causing a rotating probe of a friction stir welding tool to enter a workpiece or a joint region between a pair of workpieces, each workpiece being a low conductivity, high melting point metal or metal alloy, with a melting temperature above that of aluminum and a thermal conductivity less than that of aluminum, the probe extending from a shoulder and rotating relative to the shoulder, the shoulder constructed of more than one piece, the piece nearer the probe having a high melting point and being an insert defined around an aperture through which the probe extends, the working surface of all the pieces of the shoulder being in contact with the workpieces during joining and not rotating relative to the workpieces, the heat required for joining the workpieces being generated only by the rotating probe.