Flat hardness distribution in AA6061 joints by linear friction welding.

It is known that one of the main concerns associated with the conventional welding of precipitation-strengthened Al alloys is the formation of softening regions, resulting in the deterioration of mechanical properties. In this study, we show that linear friction welding (LFW) can completely suppress softening regions in precipitation-strengthened AA6061-T6 alloy by introducing a large shear strain and by controlling the interfacial temperature. We found that the LFW process resulted in an extremely low interfacial temperature; it decreased as the applied pressure increased from 50 to 240 MPa. This approach can essentially suppress both softening and hardening regions, leading to uniform hardness distribution in Al joints. The high-pressure LFW process demonstrated here can thus provide an innovated guidance to obtain high-performance Al alloy joints and be extended to other precipitation-strengthened Al alloys, which undergo high-temperature softening.