Investigation of residual strains by neutron diffraction in an AZ31 direct chill cast billet

Neutron diffraction data was collected, showing the strain distributions along radial, axial and hoop directions in a direct chill cast billet of AZ31 magnesium alloy. Strain measurement by neutron diffraction is a non-destructive technique that uses the diffraction of a beam of thermal neurons to determine the atomic spacing within a small gauge volume inside polycrystalline materials. The benefits of using neutrons versus X-rays lie in the increased penetration depth achieved with neutrons, which can allow measurement of the internal strains several centimeters away from the material surface. A data-processing technique was proposed to assess and remove the irregular points, and the point-to-point fluctuations were evaluated. Residual strain measurements on the as-cast billet contribute direct observation of the stress/strain state in the billet. And the results also provide the data necessary to validate a thermo-mechanical model that predicts the evolution of stress/strain during the DC casting and subsequently to investigate the cracking defects in the billets.