Mechanical properties and microstructural characteristics of an Al-Mg alloy with bimodal grain size at room and elevated temperatures

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University of Alabama Libraries

The strength of aluminum alloy 5083 has been shown to be significantly improved when it is engineered to have a bimodal grain size consisting of coarse grains (CGs) embedded in an ultrafine grained (UFG) matrix. This study investigates how a variety of parameters including strain rate, temperature, specimen thickness, CG ratio, and anisotropy affect the mechanical properties of this material when tested in uniaxial tension. The material is fabricated through cryomilling, cold isostatic pressing, and extrusion. A full factorial experiment is designed and implemented to test these effects on the material. Post-test examination of the specimens with optical and electron microscopes is conducted in order to gain a deeper understanding of the material's fracture behavior. While the material shows greatly improved strength compared to conventional Al-Mg alloys at room temperature, its strength rapidly decreases with rising temperature such that by 473 K, it was observed to be weaker than conventional Al 5083 at the same temperature. Dynamic recovery was observed in high temperature tests and the amount of recovery was found to depend on the material's CG ratio. Strain rate sensitivity was observed in the material at all temperatures. Significant differences were observed both in the material's properties and its fracture surface when the specimens were loaded parallel or perpendicular to the extrusion direction. A constitutive model based on Joshi's model of plasticity was developed to describe the material's room temperature behavior.

Electronic Thesis or Dissertation
Mechanical engineering