The Creep-Rupture Embrittlement of Metals as Exemplified by Aluminum

Abstract

Creep-rupture tests have been conducted on a variety of alloys made from high-purity aluminum to which was added iron and silicon, both separately and in combination. The investigation was designed to provide information on the creep-rupture embrittlement of aluminum as influenced by composition and temperature, and to establish the rate at which embrittlement occurred in the tests.

Iron, by itself, was found to embrittle aluminum. The embrittling effect of silicon, by itself, was negligible. Tests on alloys containing iron alone had a tendency to show minimum ductility at intermediate times to failure. Alloys with both iron and silicon also showed minimum ductility at about the same time to failure, but this minimum was at lower ductility values, and remained constant, for each test, at longer times to failure. Increments of iron above about 0.1 per cent do not necessarily confer increasing embrittlement.

Annealing at higher temperatures improves the ductility of these alloys, as shown by tests at lower temperatures.

The rate of embrittlement, at testing temperatures where embrittlement is pronounced, is very slow in the early stages of a test but accelerates rapidly near the end.

The results of the investigation confirm a previously stated postulate that impairment of cohesion across grain boundaries, by impurities accumulated in the course of creep-rupture tests of metals, is a necessary and sufficient condition for the development of intercrystalline embrittlement.