Fletcher Aluminium is a New Zealand company that manufactures aluminium extrusions for the building market. Their extrusion process involves using a hydraulic ram to force heated raw supplied material, in the form of large diameter cylindrical logs, through a die land that is the desired product shape. The final quality of the extruded product is influenced by the extrusion temperature, ram pressure and extrusion speed. The speed of extrusion at Fletcher Aluminium is limited by the extrusion ram pressure because the extrusion machine is operating at the pressure limit of the compressor. Currently the company requires an increase in the extrusion speed, while maintaining quality requirements where these improvements are desired without upgrading the compressor. The press pressure is required to overcome friction and the flow stress of the billet, which is dependent on the precipitates and solutes conditions and their strengthening effects in the billet. However, the preheating temperature and extrusion speeds need to be sufficiently low enough to avoid hot tearing. This research starts to increase the ram speed by decreasing the Mg2Si content for precipitation strengthening. Heat treatment may be used to dissolve Mg2Si content by billet preheat to a temperature at or exceeds solvus temperature (TSolvus). However, a higher (than TSolvus) billet temperature may have two conflicting effects. First, a higher temperature in general reduces the flow stress thus lowering the required pressure. On the other hand, at temperature higher than Tsolvus, Mg2Si should completely dissolve, resulting in solid solution strengthening thus increasing the flow stress. The objective of the study is to quantify the strengthening contributions from solute atoms (Mg / Si) and precipitates (Mg2Si) on the as-received and heat treated test samples using room temperature mechanical testing and phase diagram analysis. The selected heat treatment conditions fully enclose the preheating temperature and time range currently used in Fletcher Aluminium production. Simulations of the extrusion were conducted by hot compression testing (Gleeble test), to measure the combination of strengthening effects during deformation at elevated temperatures. The room temperature tests have shown that hardness, yield strength (YS) and ultimate tensile strength (UTS) are minimised at approximately 405°C. The minimum point is shown to be caused by the combination of strengthening and softening due to solid solution and precipitation strengthening. The higher values of hardness, YS and UTS at lower and higher preheating temperatures are mainly due to precipitation and solution strengthening respectively. The findings show that, the solution of Mg2Si gradually increases as the temperature increases at temperatures exceeding 405°C. Hardness, YS and UTS were compared in order to determine the correlation between each mechanical property. A correlation exists, but it is not simple to translate between each mechanical property. The relationship between hardness and stress observed for 8% permanent strain was also investigated; there was no improvement in correlation. The elevated temperature tests show that initial flow stress and peak flow stress reduces linearly with temperature increases, which means higher testing temperature results lower precipitation and solid solution strengthening effects. Additionally, the constants of the Gleeble – Holomon equation were numerically calculated and are similar to published values. The Gleeble – Holomon equation was combined with Felthams equation in order to provide a relationship between extrusion velocity and extrusion temperature.

Fletcher Aluminium is a New Zealand company that manufactures aluminium extrusions for the building market. Their extrusion process involves using a hydraulic ram to force heated raw supplied material, in the form of large diameter cylindrical logs, through a die land that is the desired product shape. The final quality of the extruded product is influenced by the extrusion temperature, ram pressure and extrusion speed. The speed of extrusion at Fletcher Aluminium is limited by the extrusion ram pressure because the extrusion machine is operating at the pressure limit of the compressor. Currently the company requires an increase in the extrusion speed, while maintaining quality requirements where these improvements are desired without upgrading the compressor. The press pressure is required to overcome friction and the flow stress of the billet, which is dependent on the precipitates and solutes conditions and their strengthening effects in the billet. However, the preheating temperature and extrusion speeds need to be sufficiently low enough to avoid hot tearing. This research starts to increase the ram speed by decreasing the Mg2Si content for precipitation strengthening. Heat treatment may be used to dissolve Mg2Si content by billet preheat to a temperature at or exceeds solvus temperature (TSolvus). However, a higher (than TSolvus) billet temperature may have two conflicting effects. First, a higher temperature in general reduces the flow stress thus lowering the required pressure. On the other hand, at temperature higher than Tsolvus, Mg2Si should completely dissolve, resulting in solid solution strengthening thus increasing the flow stress. The objective of the study is to quantify the strengthening contributions from solute atoms (Mg / Si) and precipitates (Mg2Si) on the as-received and heat treated test samples using room temperature mechanical testing and phase diagram analysis. The selected heat treatment conditions fully enclose the preheating temperature and time range currently used in Fletcher Aluminium production. Simulations of the extrusion were conducted by hot compression testing (Gleeble test), to measure the combination of strengthening effects during deformation at elevated temperatures. The room temperature tests have shown that hardness, yield strength (YS) and ultimate tensile strength (UTS) are minimised at approximately 405°C. The minimum point is shown to be caused by the combination of strengthening and softening due to solid solution and precipitation strengthening. The higher values of hardness, YS and UTS at lower and higher preheating temperatures are mainly due to precipitation and solution strengthening respectively. The findings show that, the solution of Mg2Si gradually increases as the temperature increases at temperatures exceeding 405°C. Hardness, YS and UTS were compared in order to determine the correlation between each mechanical property. A correlation exists, but it is not simple to translate between each mechanical property. The relationship between hardness and stress observed for 8% permanent strain was also investigated; there was no improvement in correlation. The elevated temperature tests show that initial flow stress and peak flow stress reduces linearly with temperature increases, which means higher testing temperature results lower precipitation and solid solution strengthening effects. Additionally, the constants of the Gleeble – Holomon equation were numerically calculated and are similar to published values. The Gleeble – Holomon equation was combined with Felthams equation in order to provide a relationship between extrusion velocity and extrusion temperature.

Thèse (D.Eng.) -- Université du Québec à Chicoutimi, 2008. / La p. de t. porte en outre: Doctorat en ingénierie, thèse pour l'obtention du titre de Philosophiae Doctor en ingénierie. CaQQUQ Comprend des réf. bibliogr. (f. 174-178). Publié aussi en version électronique. CaQQUQ

Thèse (D.Eng..) -- Université du Québec à Chicoutimi, 2008. / La p. de t. porte en outre: Thèse présenté[e] à l'Université du Québec à Chicoutimi comme exigence partielle du doctorat en ingénierie. CaQQUQ Comprend des réf. bibliogr. (f. [292]-314). Publié aussi en version électronique. CaQQUQ

Mémoire (M. Sc. A.)-- Université du Québec à Chicoutimi, 1984. / Bibliographie: f. 101-102. Document électronique également accessible en format PDF. CaQCU

Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2006. / Bibliogr.: f. 127-129. Document électronique également accessible en format PDF. CaQCU

Thèse (M.Sc.)--Université Laval, 2009. / Bibliogr.: f. 95-98. Publié aussi en version électronique dans la Collection Mémoires et thèses électroniques.

Th.--Sci. phys.--Grenoble 1, 1978. N°: 86.

In addition to being one of the highest strength non-heat treatable aluminium alloys, magnesium-alloyed wrought aluminium 5083 displays excellent corrosion resistance and good weldability. Aluminium alloy 6061, alloyed with magnesium and silicon, displays high strength, excellent formability, adequate weldability and good corrosion resistance. These aluminium alloys find application in the ship building and transport industries where 5083 is often joined to 6061 to produce welded structures such as complex I-beams and semi-hollow or hollow channels. This project aimed at characterizing the hardness, tensile properties, corrosion behaviour and fatigue properties (in air and in a 3.5% NaCl solution) of aluminium 5083 and 6061 in the as-received and welded conditions. Plates of 5083-H111 and 6061-T651 aluminium, prepared with double-V or square butt joint preparations, were joined using semi-automatic or fully automatic pulsed gas metal arc welding (GMAW). The pulsed GMAW process allows close control over the welding arc and facilitates the use of lower average heat inputs, thereby improving the bead appearance and mechanical properties. During this investigation, three filler wires were evaluated, namely magnesium-alloyed ER5183 and ER5356 aluminium, and silicon-alloyed ER4043. Hardness measurements revealed a decrease in hardness in the weld metal of the 5083-H111 welds. Dressed welds failed in the weld metal during transverse tensile testing, whereas undressed (as-welded) specimens failed at the weld toe or weld root due to the stress concentration introduced by the weld geometry. Significant softening, attributed to the partial dissolution and coarsening of strengthening precipitates and recrystallization during welding, was observed in the heat-affected zones of the 6061-T651 welds. During tensile testing, failure occurred in the heat-affected zone of all 6061 welds. Welding reduced the room temperature fatigue life of all specimens tested. In the 5083 welds, fatigue cracks initiated preferentially at gas pores, lack-of-fusion type defects and second phase particles in dressed welds, and at the stress concentration presented by the weld toes or the weld root in undressed welds. In 6061 welds, failure occurred preferentially in the softened heat-affected zone of the welds. As a result of improved control over the weld profile and a lower incidence of weld defects, fully automatic welds consistently outperformed semi-automatic welds during fatigue testing. The presence of a corrosive environment (a 3.5% NaCl solution in this investigation) during fatigue testing reduced the fatigue properties of all the samples tested. Corrosion pits formed preferentially at second phase particles or weld defects, and reduced the overall fatigue life by accelerating fatigue crack initiation. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Materials Science and Metallurgical Engineering / unrestricted

L'utilisation accrue de l'aluminium structural au cours des dernières décennies s'explique par ses nombreux avantages, tels que son excellente résistance par rapport à son poids, sa résistance à la corrosion et ses bénéfices environnementaux. Dû à son coup initial élevé, l'optimisation des méthodes de conception est essentielle pour exploiter pleinement ces propriétés. Cependant, les normes actuelles utilisent des approches simplifiées pour prédire la résistance des éléments en aluminium, qui ne sont pas optimisées pour tenir compte des effets de l'écrouissage, des instabilités, des propriétés réduites dans la zone affectée thermiquement et des formes extrudées souvent complexes. Ce mémoire présente le développement d'une méthode alternative de dimensionnement des sections ouvertes en aluminium, basée sur l'Overall Interaction Concept (O.I.C.). Cette approche de conception innovante est basée sur l'interaction entre résistance et stabilité, tout en considérant les imperfections géométriques et matérielles. De plus, elle permet d'obtenir des résultats précis et cohérents par l'utilisation de courbes de flambement continues. Un modèle numérique d'éléments finis a été développé pour prédire avec précision la résistance en section des éléments en aluminium. Son efficacité a été validée en comparant les résultats à ceux de tests expérimentaux. Des études paramétriques approfondies ont ensuite été menées, permettant d'étudier l'impact de diverses géométries, d'alliages et de cas de charge sur la résistance. Avec les résultats de plus de 4500 simulations numériques non linéaires, des propositions de calculs de type O.I.C. ont été formulées pour la résistance locale des sections d'aluminium extrudées et soudées en forme de "I". La performance des propositions a été évaluée en la comparant d'abord aux résultats numériques, puis aux prévisions de résistance des normes de conception d'aluminium canadienne, européenne et américaine. Les comparaisons ont prouvé que la méthode de conception de l'O.I.C. mène à des résultats beaucoup plus précis que les normes actuelles, tout en étant plus simple et plus efficace. / The increased use of structural aluminium in the last decades can be explained by the many advantages of this material, such as its great strength-to-weight ratio, resistance to corrosion, and environmental benefits. Due to its high initial cost, optimization of design methods is essential to fully benefit of these properties. However, current standards use simplified approaches to predict the resistance of aluminium elements, that are not optimized to account for the effects of strain hardening, instabilities, heat reduced properties and often complex extruded shapes. This thesis presents the investigations conducted for the development of an alternative design method for aluminium open cross-sections, based on the Overall Interaction Concept (O.I.C.). This innovative design approach relies on the interaction between resistance and stability, and also allows to consider geometrical and material imperfections. Moreover, it allows to obtain precise and consistent results by the use of continuous buckling curves. A numerical finite element model was developed to accurately predict the cross-sectional resistance of aluminium elements. Its efficiency was validated by comparing the results to available experimental test data. Extensive parametric studies were then conducted, allowing to study the impact of various geometries, alloys, and load cases on the resistance. Using the results from more than 4500 nonlinear numerical simulations, O.I.C.-type design proposals were formulated for the local resistance of extruded and welded aluminium sections of "I" shape. The performance of the proposals was evaluated by first comparing it to the numerical results, then to the resistance predictions from the Canadian, European, and American aluminium design standards. The comparisons showed that the O.I.C. design proposal leads to much more accurate results than the current standards, while still being simpler and more efficient.