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Distinct serrations had been observed on the stress-strain curves of various steels tested previously at high temperatures (950--1100°C) at McGill University. An explanation proposed for this behavior was that dynamic strain aging (DSA), caused by the presence of substitutional elements, was taking place. To investigate the possibility that the jerky flow was caused by an interaction between dislocations and substitutional elements, the conditions of temperature and strain rate under which serrated yielding had previously been observed were explored. In addition, some of the same material was utilized in the testing. / Much of the previous work on DSA in steel has focused on the effect of interstitials, namely, carbon and nitrogen, rather than that of substitutional elements. These studies have been conducted in the blue brittle region (i.e. 100--400°C), where the diffusivity of the interstitial elements is sufficiently rapid for them to keep up with the moving dislocations. However, for substitutional elements to obtain enough mobility to induce DSA, the temperature range must be significantly higher. / The effect of substitutional elements on DSA in steel was examined in torsion and, although numerous tests were formulated and carried out in an attempt to gather evidence for this phenomenon, no firm data for the occurrence of DSA were obtained. Further experiments and analysis will be required to gain a better understanding of the behavior of DSA at elevated temperatures, particularly for the case where dynamic recrystallization is taking place. A testing method might then be devised that could make the effect of DSA more evident.

In the presence of air and oxygen, oxidation of a molten aluminum alloy will easily take place. The oxidation not only harms the operation by contributing to melt losses, but the processing of the oxides present in the melt and refractory is also costly in time and money. Refractory accretions formed due to the interactions between the oxide-layer and base refractory material, especially alumina-lined ones, are a significant problem for the industry. Aluminum alloys containing magnesium are known to oxidize much more easily and rapidly. In the foundry, oxidation of molten aluminum-magnesium alloy is more prominent than that of pure aluminum. Magnesium has a higher affinity for oxygen, causing it to oxidize more easily than aluminum. In previous studies of oxidation of aluminum alloys, it has been found that strontium additions to the alloy reduce the amount of oxidized layer in an undisturbed melt. / The effects of strontium additions on the oxidation behavior of commercial A356, A357 and 5182 aluminum alloys were investigated by monitoring sample weight gains with time with a thermo-gravimetric balance at 700, 750, and 800°C. Sample surfaces were examined using electron microscope and x-ray diffraction techniques. It was found that in the absence of Sr, the A356 and A357 samples gained substantial amounts of weight through the preferential oxidation of magnesium. Samples containing strontium had significantly lower weight gains. For the high magnesium-containing 5182 alloy, an increase of incubation period before the onset of significant oxidation is associated with the presence of strontium. This change in oxidation behavior was linked to the presence of strontium containing oxide species in the oxidizing surface.