A method of joining workpieces (1A, 1B) defining a joint region (2) comprises causing a probe (3) of material harder than the workpiece material to enter the joint region (2) and opposed portions of the workpieces (1A, 1B) on either side of the joint region while causing relative cyclic movement between the probe and the workpieces. Frictional heat is generated to cause the opposed portions to take up the plasticised condition. The probe (3) is removed and the plasticised portions allowed to solidify and join the workpieces together.
