UBC Theses and Dissertations
Tensile properties of AS-cast AA5182 aluminum alloy close to the solidus temperature Colley, Leo John
In order to address the demand for accurate property data in the partially solidified state, an experimental apparatus has been developed to enable mechanical property measurements of aluminum alloys at temperatures close to the solidus temperature and strain rates applicable to conventional casting processes. The experimental apparatus has been used to measure the tensile properties of an industrially DC cast AA5182 aluminum alloy in the as-cast condition between 500°C and 580°C, under strain rate conditions of ~10⁻⁴s⁻¹ to ~10⁻²s⁻¹. A digital camera and zoom lens were used to acquire a series of high-resolution images of the specimen diameter during testing, from which the instantaneous dimetral strain was calculated. The commercial finite element software ABAQUS™ was used to develop a 2-D axisymmetric steady-state thermal analysis of the tensile specimen in order to determine accurate deformation temperatures, and thereby the correct mechanical properties. The fracture surfaces and microstructures of the tested specimens have been examined using optical microscopy techniques, SEM and EDX analysis to develop a relationship between the mechanical properties of the alloy and changes in microstructure and fracture behaviour. Literature values of the solidification characteristics of the alloy have also been used to relate the properties and microstructure with fraction liquid. Mechanical property measurements indicate that AA5182 exhibits significant tensile strength up to a temperature of ~570°C and fraction liquid of ~0.05, after which there is a sharp drop in strength. In comparison, ductility decreased steadily with temperature, and complete loss of ductility occurred between 560°C and 570°C dependant on strain rate. Examination of the microstructure and fracture surfaces enabled these mechanical property characteristics to be linked with the presence of intergranular liquid films in the alloy. EDX analysis confirmed that the liquid films consist of melted intermetallic phases that are present in the intergranular region of as-cast alloys as a result of several eutectic reactions during the final stages of solidification.
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