An experimental and complementary FE modeling study was conducted to characterize the room and elevated temperature uniaxial compressive deformation behavior of AA7075-T6 and O-temper materials. The experiments consisted of testing cylindrical and cubic specimens prepared from a rolled and heat-treated plate stock of AA7075 alloy. The tests were conducted in the lower range of elevated temperatures up to 300 °C, at several different test speeds in rolling and transverse orientations, as well as under isothermal and non-isothermal test conditions. The test results were analyzed in terms of true stress-train responses of the two tempers under the above experimental conditions. The deformed test specimens were also observed for surface features and deformed microstructures in the interior of the specimen under the above experimental conditions. A suitable strain rate and temperature dependent constitutive hardening law, in the form of modified Voce-Kocks law, was developed and coded as a UMAT subroutine in ABAQUS FE code to simulate the uniaxial compression experiments and compare the experimental and model results. In general, good general agreement was obtained between experiments and model predictions. A suitable fracture criterion, in the form of Tresca fracture model, was also implemented as a VUMAT subroutine in ABAQUS FE code to simulate the uniaxial compression experiments and predict fracture mode and other characteristics. Once again, good general agreement was obtained between room temperature fracture shapes and model predictions. The experimental and model results collectively provide a broad-based understanding of the effect of temperature, strain rate, material anisotropy, temperature field on material flow and deformed shapes of cylinders and cubic specimens, the nature of deformation (predominantly shear along two intersecting shear directions) and fracture (predominantly shear). The constraints to deformation at the corners in the cubic specimen yielded rather complex curvature development in deformed cubes. The non-isothermal rapid heating of test specimens using electrical resistance heating and subsequent compression of the specimen provided results similar to the isothermal case. However, the electrical resistance method offers a cost-effective process to form smaller high quality components in forming modes such as hot upsetting. / Thesis / Master of Applied Science (MASc)

Weight reduction, increased fuel economy, and increased safety of structures in transportation applications has led to much interest in lightweight higher strength structural aluminum alloys. Suitable joining techniques to create such structures with aluminum sheets are required. Generally, similar and dissimilar sheet metals can be joined by adhesive bonding, welding, and mechanical fastening. Difficulty of welding and long processing times for adhesive bonding make mechanical fastening a process of much interest for joining of high strength aluminum sheets. Among the different mechanical fastening techniques available in manufacturing, clinching is a common method of joining by forming in which a punch and die are used to form a geometrical interlock. However, the process introduces surface steps on both sides of the joined sheets where one side consists of a protrusion and the other a pit. Also, clinch joining, a well-accepted and widely used process for joining ductile sheet metals, is more challenging for high strength lower ductility aluminum sheets such as AA7075. The current work aims at studying clinch-ability of high strength lower ductility AA7075 aluminum sheets of different tempers by conventional as well as a new clinching technique called "die-less" clinching. A new tooling was designed in order to conduct die-less clinches. The results showed that room temperature clinching is possible for the softer tempers namely solution treated and annealed states. However, the peak aged sheets failed to form a successful joint. A novel electrical resistance heating technique (ERH) to provide ductility to the joined sheets was used to obtain die-less clinched joints in AA7075-T6. ERH technique provides a large range of heating temperatures from room temperature to 270°C for a current duration of 3 sec. The AA7075-T6 sheets showed a superior joining by using ERH. The joint showed a metallurgical locking mechanism in addition to the commonly available form locking mechanism. / Thesis / Doctor of Philosophy (PhD) / Clinching is a common method of joining sheet metals by forming. A punch and die are used to form a permanent geometrical interlock. However, the process introduces surface steps on both sides of the joined sheets where one side consists of a protrusion and the other a pit. Clinch joining is a well-accepted and widely used process for joining ductile sheet metals. Joining of high strength lower ductility aluminum sheets such as AA7075 is more challenging. The current work aims at joining AA7075 aluminum sheets of different tempers by clinching using the conventional method as well as a new clinching technique called "die-less" clinching. The study includes a new tooling design in order to conduct die-less clinches. Also, a novel electrical resistance heating technique (ERH) to provide ductility to the joined sheets was used to obtain die-less clinched joints in the peak aged AA7075-T6. ERH technique provides a large range of heating temperatures from room temperature to 270°C for a current duration of 3 sec. The AA7075-T6 sheets showed a superior joining by using ERH.