Metallurgical Considerations in Fracture Resistance

Abstract

The application of toughness testing to alloy development has led to a number of high-strength aluminum alloys and special tempers of some alloys with outstanding combinations of strength and toughness. An underlying basis of such work arose from the findings of Staley et al. that the presence of large amounts of impurity elements such as iron and silicon, in high-strength alloys provides sites for potential crack initiation and growth as well as paths for more rapid crack growth than would otherwise be expected. The elimination of these sites would be expected to improve the toughness of the nominal composition, a concept borne out by many experiments. The combination of this principle with other optimization of compositions and thermomechanical treatments has led to the development of high-toughness alloys 2124, 2324, and 2524, all superior to 2024, and of high-toughness alloys 7175 and 7475, both substantial improvements on 7075. Similar principles have been applied to the development of newer alloys such as 7050 and 7055. One occurrence of 6061 in curve.