The fracture characteristics of austempered spheroidal graphite aluminum cast iron had been investigated. The chemical content of the alloy was C3.2, Al2.2, Ni0. 8 and Mg0. 05 (in mass percent, %). Impact test samples were produced from keel blocks cast in CO_2 molding process. The oversized impact samples were austenitized at 850 and 950℃ for 2h followed by austempering at 300 and 400 ℃ for 30, 60, 120 and 180min. The austempered sam-ples were machined and tested at room temperature. The impact strength values for those samples austempered at 400℃ varied between 90 and 110J. Lower bainitic structures showed impact strength values of 22 to 50 J. The frac-tures of the samples were examined using SEM. The results showed that the upper bainitie fracture revealed a honey Comb-like topography, which confirmed the ductile fracture behavior. The lower bainitic fractures of those samples austempered for short times revealed brittle fracture.
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