Date of Award

6-24-2022

Publication Type

Thesis

Degree Name

M.A.Sc.

Department

Civil and Environmental Engineering

Keywords

AA5182-O;Aluminum Alloy;Fracture Behaviour;Liquid Nitrogen;Plastic Deformation;Sub-Zero Temperature

Supervisor

Ahmet Alpas

Abstract

Commercial aluminum alloy AA5182 is being increasingly used as a predominant material for aircraft and automotive industries in an effort to light-weight these applications. Previous work indicates that the ductility/formability of aluminum alloys increases with decreasing temperature, however, the subject of the mechanisms behind this improvement is still up for debate. In this study, deformation and fracture behaviour of AA5182-O aluminum sheets are investigated. Tensile tests are conducted at temperatures ranging from 25 to -196℃, and a strain rate of 1.9 ×10-3 s-1, in an environmental chamber cooled with liquid nitrogen. The mechanical properties are mapped as a function of temperature. It was observed that the fracture elongation increased from 0.26 to 0.5 mm/mm from 25°C to -196°C, and that the dynamic strain aging effect was not visible at temperatures below -80℃. Cottrell-Stokes tests (temperature jump and strain-rate jump tensile tests) were conducted to evaluate the dynamic changes of mechanical properties at constant microstructure at different temperatures and strain rates. These tests provided insight on the flow dependency of AA5182-O on both temperature and strain rate. Microscopic investigation of ductile fracture at different temperatures using SEM and EDS analysis was conducted. Quantitative fractography was used to measure void sphericity, percentage, and size as function of temperature to show a transition in plastic shear deformation at 25°C to more ductile tearing deformation at -196°C.

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