Abstract
The effect of strontium (Sr) modification on the fracture characteristics is investigated in high purity Al-Si-Mg type casting alloy, AC4CH. The Charpy absorbed energy, static fracture toughness and dynamic fracture toughness of AC4CH are improved by the addition of Sr associated with the refinement and spheroidizing of needle like eutectic Si, which results in the relaxation of stress concentration of the eutectic Si. The cohesion of eutectic Si and porosity increase with increasing Sr addition. The larger size eutectic Si particles increase again with increasing Sr addition over 50ppm. These three factors seem to be the causes for decreasing dynamic toughness of AC4CH at 200ppm Sr addition comparing with 100ppm Sr addition.
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