TWI Industrial Member Report Summary 726/2001
A J Leonard
Friction stir welding of aluminium alloys is now an established joining technique. The method uses friction, generated by a specially profiled non-consumable rotating tool in contact with the surfaces to be welded, to heat and soften the metal at the interface to be joined. The rotating action of the tool then transports material from in front of the tool to the rear, mixing and forging it, creating a welded joint. A number of process variables affect the quality of the joint: tool design, rotation speed, travel speed, heel plunge depth and tilt angle; welding gap, thickness mismatch and plate thickness variation. Successful, reproducible welds may be produced by operating within process 'windows'. However, problems may arise when the welding conditions deviate from the standard operating window. In such circumstances, flaws may be generated.
There is a requirement to understand the type of flaws that may be generated, and their causes, when welding conditions deviate from the optimum. This is essential if successful corrective actions are to be taken when problems arise with production welds.
- To characterise microstructurally the types of flaws that may be generated in Al-Cu-Mn-Si-Mg aluminium alloy friction stir welds when the welding conditions diverge from the established operating window.
- To characterise surface features produced in Al-Mg-Mn friction stir welds under 'normal' welding conditions.