The investigation of the floatation of double oxide film defect in liquid aluminium alloys by a four-point bend test

ABSTRACT A mould was designed to produce considerable splashing during filling, resulting in the entrainment of freshly produced double oxide film defects. Two moulds were cast to produce 60 testbars in total, suitable for four-point bend testing, to determine their Weibull moduli. Different faces of the cast test-bars, top and bottom, would have different distributions of double oxide film defects, depending on whether the defects were expected to float or to sink during casting. The faces of the test-bars placed downwards in the four-point bend-tests would experience the maximum tensile load, meaning that the test-bar faces associated with the greatest defect densities (top or bottom) would be associated with the lowest Weibull Modulus. The experiment confirmed that double oxide film defects are positively buoyant, initially, and would float towards the surface of the casting during pouring and solidification.