alloys vacuum degassed and gas enriched were cast into conical shell molds. The castings having different quantities of gas porosities show nearly the same total shrinkage volume which decreases at higher Si contents.Pure aluminum and Al-10%Si alloy permit an unchanged volume of external shrinkage and reduced volumes of internal shrinkage with an increase in porosity volume. Al-4%Si and Al-7%Si alloys permit unchanged volumes of internal and external shrinkages respectively at lower and higher porosity levels. The volumes of internal shrinkage at higher porosity levels and of external one at lower porosity levels decrease with an increase in porosity volume. The porosity changes from a concentrated type to dispersed one with an increase in porosity volume. The gas dissolved in the melt has remarkable effects on the shrinkage morphology.
Effects of Cu on the impact strength and structures of Al-Si alloys were examined by mean s of Charpy impact test and metallographical method. The following three types of specimens were used: a) As cast. b) Solution heat treated at 500 °C for 240 min . for the above specimens. c) Artificially age hardened at 200 °C for 300 min. after the above solution heat treatment .(1) The impact strength of as cast alloys tended to be decreased with the increase in Si content and Cu addition. When Si content was low (approximately below 4%) , the strength was markedly decreased with the addition of Cu. However, the strength was gradually decreased with increasing Si content and no effects of Cu were seen on the strength at about 15% of Si content.(2) By the addition of a small amount of Cu to the hypo-eutectic alloy of nearly eutectic composition with no primary Si crystals, a marked decrease of the impact strength was seen on the specimens solution heat treated at 500 °C. The above decrease resulted from the formation of primary Si crystals due to the addition of Cu . The configuration of these primary Si crystals was the cause of stress concentration as reported in the previous paper,l~ and it was kept unchanged by holding at 500°C.(3) The impact strength of the alloys, which had been artificially age hardened at 200 °C after solution heat treatment at 500 °C, tended to be decreased with the increase in Si content and Cu additioon . Especially, the effect of Cu addition was greater than that of Si content. (Received Feb. 10, 1970)
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.