TWI Frequently asked questions
In its basic form, friction extrusion involves rotating a round bar and pressing it against a die to produce sufficient frictional heating to allow softened material to extrude through the die. As well as reducing the bar's diameter, its metallurgical features can be intentionally altered to improve the general properties of the material, due to the nature of the process and the temperatures involved.
With friction co-extrusion cladding (see illustration), the round bar is replaced by a tube with an unattached, solid core running through it. During the process, the tube is extruded at a different rate to the core which helps to disperse oxide layers and, therefore, aids the formation of a good, solid phase bond between tube and core.
TWI has successfully used the co-extrusion process to clad steel rods with both copper and aluminium. There are currently no known industrial applications.
