Thermomechanical Processing And Fatigue Of Aluminum Alloys

A review is made of the available information on thermomechanical processing of aluminum alloys, especially with respect to their fatigue behavior. An attempt is made to evaluate from the scarce and sometimes contradictory experimental evidence the possibility of improving the fatigue resistance of high-strength aluminum alloys by these treatments. To do so, it is also necessary to review the important microstructural features and deformation characteristics of these alloys, which seem to control the various stages of fatigue, and which may be influenced by the thermomechanical treatments. The discussion is limited to thermomechanical treatments subsequent to solution annealing. It is concluded that suitable processing offers the advantage of improving both strength and ductility in Al-Cu and Al-Zn-Mg-Cu alloys. If the effects of inclusions can be minimized, significant benefits are possible in fatigue, at least in Stage I crack resistance, by thermomechanical processing.

This book discusses the structure and properties of the current and potential aluminum alloys in terms of their structure (and structural transformations by new processing methods) and the relationship between structure and mechanical and other properties. The alternative materials that challenge aluminum are considered as well, since the challenge of new competitive materials is a strong influence on innovation. The book bridges the gap between current scientific understanding and engineering practice. It is an up-to-date reference that will be of use to researchers and advanced students in metallurgy and materials engineering.

A compilation of data collected and maintained for many years as the property of a large aluminum company, which decided in 1997 to make it available to other engineers and materials specialists. In tabular form, presents data on the tensile and creep properties of eight species of wrought alloys and five species of cast alloys in the various shapes used in applications. Then looks at the fatigue data for several alloys under a range of conditions and loads. The data represent the typical or average findings, and though some were developed years ago, the collection is the largest and most detailed available. There is no index.

The application of advanced metallurgical processing techniques, e.g., intermediate thermomechanical treatment (ITMT) and powder metallurgy (P/M), has produced a recrystallized X7091 P/M alloy having fine grain and particle structures and weak texture with the best overall mechanical properties compared to those of ingot metallurgical and conventional P/M alloys. The dependence of mechanical properties on grain size and particle distribution has been demonstrated among these alloys. The study of the effect of the last microstructural feature, crystallographic texture, is necessary for further property improvement through texture control.

Due to its high strength/weight ratio, 7075 aluminum alloy has been widely used as an aerospace material. However, it has relatively low fatigue strength and low fracture toughness in the T6 condition. Thermomechanical processing, including pre-cyclic loading and stretching at high and ambient temperatures, has been investigated with the aim of improving these properties. Fatigue life tests show that all four thermomechanical processes investigated increase the fatigue life at low stress levels, but cause a reduction at high stress levels. The effect of the precipitate free zone (PFZ) width on the fatigue crack propagation rate and fracture toughness has also been investigated. The fatigue crack propagation rate of the alloy with a wide PFZ was found to be approximately the same as that of the alloy with a narrow PFZ under similar conditions of cyclic loading. The alloy with the wide PFZ demonstrated a greater value of fracture toughness than that shown by the alloy with the narrow PFZ. These experimental results have been analyzed taking recently proposed theoretical models into account. Transmission electron microscopy showed that a large number of dislocations were generated within the soft PFZ areas as a result of the cyclic pre-loading. This is believed to contribute to the increase in fatigue life at low applied stress levels. Scanning electron microscopy has shown an intergranular fracture mode for the alloy with the narrow PFZ and a dimple rupture mode for the alloy with the wide PFZ.

A comprehensive treatise on the hot working of aluminum and its alloys, Hot Deformation and Processing of Aluminum Alloys details the possible microstructural developments that can occur with hot deformation of various alloys, as well as the kind of mechanical properties that can be anticipated. The authors take great care to explain and differenti