Thermal treatments for tailoring the microstructure and wear behaviour of friction stir processed Aluminium-C fibres composites

A new and simple method for the production of metal matrix composite by friction stir processing (FSP) sandwiches made from metal sheets (e.g. Mg- or Al-based alloy) intercalated with a reinforcing material e.g. a carbon fabric has recently been devised by the present authors [A. Mertens et al., Mater. Charact. 107 (2015), 125-133]. This process allowed the production of large-size sound metal matrix composites, but the usage properties (e.g. wear resistance,...) of these composites are not yet optimised. Indeed, the matrix of the composite may be softened after processing as FSP is known to cause dissolution of the precipitates responsible for strengthening Mg- or Al-based alloys [A. Simar et al., Mater. Sci. Eng. A 486 (2008), 85-95]. This work thus aims at investigating the potential of thermal treatments for tailoring the microstructure and wear behaviour of age hardenable aluminium alloy 6005 – C fibres composites.
The effect of (solution and) ageing treatments on the microstructure and hardness of FSPed Al-C composites has been investigated using optical and scanning electron microscopy, along with Vickers hardness tests. The wear behaviour of the as-FSPed and of the heat treated specimens has been characterized using a pin-on-disc tribometer. Moreover, reference AA6005 samples without C fibres have been produced and tested under similar conditions. The comparison of the reference and of the composite samples allows a better understanding of the role of the C fibres in controlling the grain size of the Al matrix by influencing recrystallisation during FSP and grain growth during thermal treatments.