Abstract
This article describes the effect of friction welding conditions and aging treatment on the mechanical properties of type 7075-T6 aluminium alloy (A7075) friction welded joints. A7075 was joined by using a continuous drive friction welding machine with an electromagnetic clutch in order to prevent braking deformation during as rotation speed decreases. That is, it was welded by using the ‘Low Heat Input Friction Welding Method’ (LHI method) developed by the authors, in which heat input is lower than in the conventional method. The maximum joint efficiency at a friction pressure of 30 MPa was approximately 25%, and that at 90 MPa was approximately 64%. These joints were made without forge pressure. The low joint efficiency was due to the existence of non-joined regions at the welded interfaces. However, the welded joint had approximately 82% joint efficiency when the friction time was 0·5 s at a friction pressure of 90 MPa with a forge pressure of 180 MPa. The welded joint softened at the welded interface and its adjacent region. It had approximately 90% joint efficiency after aging for 730 days at room temperature (natural aging). It also had approximately 95% joint efficiency after aging for 48 h at 393 K (120°C), and had no softened region at the welded interface. The heat input of the welded joint with the LHI method could be decreased to approximately 50% of that with the conventional method. The LHI method has several advantages for A7075 friction welding; less heat input than with the conventional method, and light post-weld processing (machining, etc.) because the flash can be minimised.
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