Stress corrosion cracking behavior of friction stir processed ultrafine grained light metal alloys
"The influence of friction stir processing (FSP), a microstructural modification tool, on the corrosion behavior of Al-Mg, Al-Mg-Sc, Mg-Al-Zn and Mg-Y-RE alloys has been studied. An attempt has been made to establish correlation between processing parameters and the subsequent microstructural evolution especially matrix grain size on the corrosion and stress corrosion properties of the alloys. A relationship between grain size and corrosion rate for Mg-Y-RE alloys was envisaged and power law type behavior was proposed. Ultrafine fine grained (UFG) microstructure showed one order magnitude lower corrosion rate. Grain refinement achieved through different FSP parameters showed lower corrosion currents for Al-Mg alloy as compared to the base alloy. The significant increment in linear polarization resistance of UFG Al-Mg-Sc alloy has been attributed to modification in chemistry and grain refinement. The slow strain rate testing (SSRT) results indicated no stress corrosion susceptibility for FSP Al-Mg alloy. A critical grain size for Al-Mg alloys has been proposed to show optimum general corrosion resistance with no stress corrosion cracking (SCC) susceptibility. AZ31 microstructures showed significant loss of ductility during SSRT in corrosive medium indicating high SCC susceptibilities. The higher SCC resistance of over aged Mg-Y-RE microstructure as compared to under aged and peak aged was attributed to the alteration in microchemistry and precipitate morphology in the matrix"--Abstract, page iv.
Missouri University of Science and Technology
Networked Digital Library of Theses and Dissertations