Measurement of as-cast residual stresses in an aluminium alloy AA6063 billet using neutron diffraction

Machining and sawing Aluminium DC cast products without a stress relief treatment can lead to uncontrolled distortion, crack formation, and significant safety concerns due to the presence of thermally-induced residual stresses created during casting. Numerical models have been developed to compute these residual stresses and yet have only been validated against measured surface distortions. In the present contribution, the variation in residual strains and stresses in the steady state regime of casting have been measured as a function of radial position using neutron diffraction in an AA6063 grain-refined cylindrical billet. A thernio-mechanical finite element model was used to determine the minimum section-length which can be sawed from the billet without significantly relaxing the residual stresses while conforming to the requirements of the neutron diffractometer. The results of the neutron diffraction measurements compare favorably with the numerical model, in particular the depth at which the axial and hoop stresses change sign. Such results provide insight into the development of residual stresses within castings.