Effect of ingate velocity on bubble damage in Al-5Mg and 413 Casting Alloys

Bubble damage is a casting defect related to the air entrainment as a result of unsuitable running system design and surface turbulence. In this work, effects of gate velocity on the formation of bubble damage in Al-5Mg and 413 casting alloys are investigated. Gate velocity was changed by increasing the sprue height and decreasing the ingate area. After casting radiography of plates and three points bend test, on samples taken from plates, was performed. Fractography of samples by SEM and quantitative analysis by EDS were also applied. Results show that size and quantity of entrapped air bubbles are increased as a result of increase in gate velocity. Area fraction and size of bubbles entrained in Al-5Mg alloy seems to be eight folds higher in comparison with 413 Al alloy. This observation confirms the hypothesis of the effect of oxide films thickness on the intensity of bubble damage in various Al alloy.