Damage evolution in ductile metals is characterized by the nucleation, growth and coalescence of voids. In aluminium alloys, the void population generally nucleates by the decohesion or fracture of the iron rich intermetallic particles. Previous studies have shown that the nucleation stress increases when the size of the intermetallic particles decreases retarding the final fracture of the material. Furthermore, initial porosities and particle clustering reduce the fracture strain. Hence, friction stir processing (FSP) has been applied to a 6xxx series aluminium alloy in order to eliminate initial porosity, break the intermetallic particles and distribute them more homogeneously to improve the fracture strain. Detailed characterization involving 3D microtomography has confirmed that the size of particles is reduced and that void nucleation is delayed. Furthermore, elimination of initial porosity and homogenization of the intermetallics spatial distribution has been quantified. Tensile tests have confirmed an increase of the fracture strain of the material.
Hannard, F., Castin, S., Maire, E., Mokso, R., Pardoen, T., & Simar, A. (2017). Effect of friction stir processing on the damage resistance of 6xxx series aluminium alloys. TMS 2017, San Diego, USA. https://hdl.handle.net/2078.5/93651