Residual stress evolution with compressive plastic deformation in 6061Al-15Â vol.% SiCw composites as studied by neutron diffraction

The evolution of the residual stress (RS) with compressive plastic deformation of several discontinuously reinforced 6061Al-15 vol.% SiCw metal-matrix composites (MMCs) has been investigated. The composites were obtained by a powder metallurgical route and heat treated to a fully hardened, T6 condition. The RS was determined from neutron diffraction. The results show that deformation relaxes the hydrostatic component of the macroscopic RS (M-RS) progressively until a minimum is reached, around 2-5% plastic strain. Similarly, the hydrostatic component of the microscopic RS (m-RS) relaxes rapidly with deformation. Relaxation continues with further strain and at ≈15% this m-RS component disappears. The deviatoric components of both the M-RS and the m-RS, however, remain unaltered with increasing plastic strain. The increase of the full width at the half maximum (FWHM) of the Al diffraction peaks with strain reveals the increased lattice distortion and microscopic RS gradient around the reinforcing particles. The linear correlation found between the FWHM of the two phases suggests also the activation of a lattice distortion transfer mechanism from the Al phase to the SiC phase.