A new methodology for measurement of semi-solid constitutive behavior and its application to examination of as-cast porosity and hot tearing in aluminum alloys

Hot tearing and as-cast porosity are the two defects which impede the performance of cast products. The effect of porosity on hot tearing was investigated using a novel semi-solid tensile deformation methodology combined with X-ray micro-tomography. Semi-solid deformation tests were conducted on the commercial aluminium-magnesium alloy AA5182 in the as-cast state. This material was tested in two forms: as-received and hot isostatically pressed. In all cases, processing via hot isostatic pressing was found to increase the semi-solid tensile strength and ductility by reducing the number of pre-existing nucleation sites for strain accommodation. Further, it was shown that the failure in this material is localized to the fracture surface with very little internal damage occurring in other areas. These results support the hypothesis that as-cast porosity is intimately linked to the hot tearing susceptibility of aluminum alloys. (C) 2008 Elsevier B.V. All rights reserved.