The effects of oxide film defects on the strength and reliability of 319 alloy castings

The effects of runner system design on the reliability of cast 319 aluminum alloy are analyzed by the Weibull cumulative distribution. Filtered and unfiltered sand moulds were used to produce tensile test bars. Significant differences were found between the two populations. Samples with low UTS values were found to contain oxide film defects on the fracture surface. By quantifying the size of the film defects it was possible to employ a fracture mechanics based model to predict the fracture strength of these samples. This was shown to be in good agreement with the experimental results. The presence and size of oxide film defects was demonstrated to govern the strength and reliability of these castings.