Stirring Solid Metals to Form Sound Welds

Friction stir welding does not generate fumes and there is no loss of volatile alloying elements. This remarkable process maintains the solid state during welding and yet is able to fabricate structurally sound joints. A robust spinning-tool rubs against the abutting parts that require joining, generates heat by friction, thus softening the metals without melting it. The translation of the spinning-tool along the joint line forges the pieces together under great pressure. It is almost like locally and forcefully mixing the two sides of the joint together without changing the overall shape although the flow pattern during this mixing is asymmetrical. The lack of melting means that it is possible to join dissimilar metals or very difficult metals that cannot otherwise be joined. In spite of its relatively recent invention, the process is now ubiquitous in the welding of aluminium alloys in particular, but with many efforts to extend its horizon, for example, to the microelectronics field.