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Neutron Diffraction Measurement of Residual Stresses in Friction Stir Processed Nanocomposite Surface Layer

Friction stir processing (FSP) was successfully used to stir and mix nano-sized Al2O3 particles into a Al6061-T6 aluminum plate to form a nanocomposite layer up to 3 mm thick. This nanocomposite surface has demonstrated significantly improved surface hardness, yield strength, and wear-resistance without sacrificing the substrate ductility and conductivity. Neutron diffraction analysis was conducted to determine the residual stress distribution in the nanocomposite surface layer. For comparison, the residual stress of the aluminum surface that was processed similarly but had no particle involved was also measured. Results showed that the macro-level residual stresses in the FSP zone without particles are low due to the annealing effect induced by the long heating time and large heat input. The macro-level residual stresses in the FSP-processed Al-Al2O3 nanocomposite zone are tensile up to 100 MPa in all three directions. The details of the results will be further discussed in the paper.