The Microstructure and Deformation Behavior of Al-Fe-Mn Alloys with Different Fe Contents during Cold Rolling

The microstructure transformations and deformation behavior of Al-Fe-Mn alloys with different Fe contents during their cold rolling process were investigated by means of hardness testing, conductivity testing, and transmission electron microscopy. It was observed that the hardness of the two alloys increased initially along with the levels of cold rolling reduction, then reduced when levels of cold rolling reduction increased further. Two kinds of deformation behaviors, work hardening and work softening, were observed during cold rolling for both Al-Fe-Mn alloys with different Fe contents. The critical level of cold rolling reduction that led to the change from work hardening to work softening was different in both alloys and the critical level of cold rolling reduction of the alloy with high Fe content was significantly lower than that of the alloy with low Fe content. During the work hardening process, the number of dislocations in the alloys increased continuously as the level of cold rolling reduction increased and they were accompanied by the formation of substructures. After the occurrence of work softening, the dislocation density in the alloys was significantly reduced. The sub-grain structures polygonized and ultimately transformed into equiaxed sub-grains.

A Study on the Deformation Dehaviours of Al-1.4Fe-0.2Mn Alloy Sheets

The deformation behaviours and microstructure transformations during the cold rolling process of Al-1.4Fe-0.2Mn alloy sheets prepared from 99.7% pure aluminium were investigated by means of hardness-testing, transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS). The phenomena of work hardening and work softening were observed. The hardness of Al-1.4Fe-0.2Mn alloy sheets increased with the increasing of cold rolling reduction firstly, and reached to a peak at 80% cold rolling reduction, meaning work hardening. However, with further increasing of cold rolling reduction, the hardness decreased, which indicates work softening. During the initial deformation stage, the dislocation density and the number of sub-grain structures increased gradually, and many dislocations formed tangles, resulting in work hardening. When the cold rolling reduction exceeded 80%, the dislocation density decreased and sub-grain structures polygonized, leading to work softening. The forming of Mn, Fe and Si bearing compounds is an important reason for the work softening due to lowering solid solution content.

Work Softening and Low Cycle Fatigue of Molybdenum Alloy under Force-Controlled Loading and Elevated Temperatures

Low cycle fatigue (LCF) of a molybdenum alloy was investigated under force-controlled cyclic tension with a zero minimum stress within the 850 – 1300 °C temperature range using Gleeble-3800 physical simulator. Also, the work softening (hardening) behavior was examined through a monotonic tension up to fracture after the force-controlled cyclic deformation. The investigated material under a force-controlled cyclic loading tends to work softening and its tensile strength decreases until the applied stress. The LCF fracture in such conditions occurs through the unrestricted plastic (creep) strain accumulation and exhaustion of the plasticity. The Morrow-type fatigue curves were obtained from the tests. The results of work softening tests were also used to predict the fatigue life.