Al–Mn–Mg alloys have been considered as the most suitable basket material of transport and storage casks for spent nuclear fuels. However, the Mg content should be defined with consideration of their prospective heat histories; e.g. exponentially decreasing in temperature from about 200 to 100°C during the fuel storage up to 60 years. In this research, precipitation behavior of β phase (Al3Mg2) in Al–Mn–Mg alloys was analyzed at various temperatures, focusing on the effects of the amount of Mg. Time-temperature-precipitation (TTP) diagrams for these alloys were depicted by a model which had been developed based on classical nucleation theory. The TTP diagrams were further rebuilt to “degree of supersaturation-diffusion length-precipitation (SLP) diagram”, where the degree of supersaturation (S) and diffusion length multiplied by cubic root of Mg concentration (L*′) were involved for predicting the starting condition of precipitation. From the SLP diagram, Mg content of 1.0 mass% was found to be able to maintain sufficiently the solid solution strengthening for 60 years.
The effects of crystal lattice rotation and crystal orientation were analyzed in cyclic bending for aluminum wire. Typical result was improvement of cyclic bending properties in aluminum wire suggested that grain refining and DD//〈111〉 preferred orientation were effective. Grain refinement is indicated to suppress crystal lattice rotation near the grain boundaries in cyclic bending deformation and increase the number of cyclic bending fractures. The feature of intergranular crack formation in cyclic bending deformation is that there is Burgers vector of the primary slip system’s that is perpendicular to the grain boundaries inclined 45° with the primary stress axis and parallel to the ND plane. These are not present in DD//〈111〉 grains, but are present in DD//〈001〉 grains. These facts are speculated that DD//〈111〉 crystal grains delay the formation of intergranular cracks, the number of cyclic bending fracture depends on texture.These results give design and manufacturing guidelines for aluminum wire conductors for automotive wire harness with excellent cyclic bending properties by DD//〈111〉 preferential orientation of aluminum wire.
The effects of Al concentration and Zn addition on the corrosion resistance of Mg–Al–(Zn)–Ca based magnesium (Mg) alloy rolled sheets were investigated. AXM (Mg–Al–Ca) alloys containing 1 mass%Ca, and AZX (Mg–Al–Zn–Ca) alloys containing 1 mass% of Ca plus 1 mass%Zn, both adjusted the Al concentration to 6, 7, 8, 9, 11 mass%, were prepared. The corrosion resistance of alloys in 5 mass%NaCl solution was evaluated by the weight loss and the penetration depth. Electrochemical method based on corrosion potential and impedance spectroscopy was applied to monitor the corrosion behavior. The surface film formed on the alloy surface was characterized by GD-OES and SEM/EDS. The corrosion rates were minimal for AXM alloy with Al content of around 8 mass%Al whereas AZX alloy showed the opposite result with the same content. The reason was interpreted in terms of the Al concentration in the matrix (α phase). The tendency of localized corrosion in high Al-containing Mg alloys was pointed out.
In this study, the multi-pass high-pressure sliding (MP-HPS) process was applied for grain refinement of Al–3Mg–0.2Sc (mass%) rods with an upsized dimension of 16 mm in diameter. To achieve a homogeneous microstructure throughout the cross-section, the rod sample was rotated with 60° around the longitudinal axis (MP-HPS-R) for three times. A microstructure with an average grain size of 280 nm was developed around the center of the cross-section through the MP-HPS-R process. Superplasticity with total elongations of more than 400% was achieved in the 9 mm diameter range on the cross-section of the MP-HPS-R-processed rod.