An X-ray microtomographic and finite element modeling approach for the prediction of semi-solid deformation behaviour in Al-Cu alloys

There is a dearth of published experimental measurements of flow stress behaviour of semi-solids, yet it is critical for simulating phenomena ranging from the processing of metals to the flow of magma. In this paper, a method for calculating flow stress behaviour of semi-solids was developed using a combination of high-temperature compression testing, X-ray microtomography (XMT) imaging and direct finite element modeling (DFEM). This novel methodology was applied to columnar dendritic structures in semi-solid Al-Cu alloys via first quantifying the complex geometry of the semi-solid using XMT. Then these three-dimensional datasets were meshed and their behaviour was simulated using DFEM to derive the stress-strain relationship with a fraction solid (fS) dependency term. The mechanical behaviour of the solid dendrites near the liquidus temperature was not available in the literature; therefore, samples were fabricated and compression tested using a Gleeble 3500 thermomechanical simulator. The resulting XMT-DFEM-derived constitutive equation predicts the flow stress behaviour of semi-solid in the range of fS equal to 0.1-0.9, showing good correlation to prior experimental data for both other aluminium and ferrous alloys. © 2009 Acta Materialia Inc.