Towards Improved Hybrid Joining of Aluminum Alloys to Carbon Fiber Composites With Friction Stir Welding

The current methods for welding aluminum alloys to carbon fiber composites rely heavily on the adhesive bond created when a melted polymer solidifies in contact with the aluminum surface. This bond may be improved by achieving mechanical interlocking of the carbon fibers and the aluminum alloy, so that load bearing fibers contribute to the bond strength. Friction Stir Welding (FSW) holds potential as a process to achieve such interlocking by locally heating and plasticizing the metal under significant load to cause infiltration of the metal into the carbon fiber weave. During preliminary investigations, AA6061-T6 was friction stir welded in contact with dry carbon fiber bundles, and the infiltration of aluminum into the fibers was measured. The results were compared to an accepted polymer infiltration model that was adapted for aluminum infiltration, giving promising initial agreement. This suggests that the plasticized aluminum in FSW can be treated as a fluid with an effective viscosity, and that well established polymer infiltration models can form the base of a metal composite FSW model.