STATISTICAL DISTRIBUTIONS OF FRACTURE STRENGTHS OF CAST AL-7SI-MG ALLOY

Al-7Si-Mg alloy vertically cast test bars were produced in dry sand mo ulds by top filling (TF), turbulent bottom filling (TBF) and turbulenc e-free bottom filling (TFBF) with filtered metal. The test bars were h eat treated prior to tensile testing. Scanning electron microscopy exa mination of polished sections showed that all the test bars contained tangled networks of oxide films which are seen to constitute cracks wi thin the metal. They are more prevalent in the TF and TBF castings. A large number of anomalous features are observed on all fracture surfac es. These are oxide films produced during filling and entrained in the casting. The best description of the skewed distributions of tensile strengths of each set of castings was obtained with the Weibull distri bution. Weibull slopes of 11, 20 and 38 were obtained for the TF, TBF and TFBF castings respectively.