This study investigated the effect of hot rolling temperature on microstructure formation during annealing of a hotrolled Al-1%Mn alloy. After casting, samples were hot rolled at 300°C, 400°C, and 500°C with a reduction ratio of 80%, and then annealed at 300°C, 400°C, and 500°C for various times. Vickers hardness test and electrical conductivity measurements were performed on each annealed sample. Some samples were subjected to FE-SEM/BSE and FE-SEM/EBSD to obtain information on precipitates and crystal orientation. The results obtained suggest that recovery mainly occurred in all the hot-rolled samples when annealed at 300°C, and that recrystallization was completed when annealed at 500°C. At 400°C, the microstructure formation behavior changed depending on the hot rolling temperature, and the change in electrical conductivity suggested that precipitation and recrystallization competed with each other.

Effect of annealing in hot-rolled Al-Mn alloys on evolution of microstructures was investigated using hardness measurement, electrical-resistivity measurement, backscattered electron images, and its image analysis. Electrical resistivity with annealing time exhibited that residual content of solute Mn and Fe atoms remained in hot-rolled alloys, and that their number was decreased during annealing. Analysis of backscattering electron image of scanning electron microscopy provided that a lot of precipitates grew by consumption of such solute atoms. We considered that the growth of precipitates during isothermal annealing affect recovery and recrystallization and then hardness behavior.

Precipitates formed during the hot-rolling process of Al-1%Mn alloy were quantitatively characterized by 3-dimensional (3-D) evaluation. The 3-D image was reconstructed using a serial sectioning technique by combining the focused ion beam and scanning electron microscopy (SEM). In the reconstructed 3-D volume, more than 10000 precipitates were extracted, and the log-normal distribution explained the size distribution well. We also quantitatively evaluated the precipitates from the 2-dimensional (2-D) SEM image taken during the serial-sectioning and from the scanning transmission electron microscopy (STEM) observation that the specimen was fabricated from the serial-sectioned sample. According to the data evaluated from the 2-D and the 3-D images, the average size of the precipitation measured by the 3-D image was larger than that of the 2-D images of SEM and STEM. That is presumed by the morphological anisotropy owing to hot rolling. We also discussed the effect of the number of the analyzed precipitates on the average size and distribution. The average size significantly depends on the number of analyzed precipitates. Besides, we evaluated the normality of the logarithmic distribution of the size by the Quantile-Quantile plot.

An in-situ XRD measurement system using synchrotron radiation was developed to investigate the effect of deformation temperature on the change of dislocation density during deformation. In A1200 aluminum, the dislocation density hardly changed during plastic deformation at room temperature. On the other hand, it decreases with increasing strain as the deformation temperature increases. The stress at which dislocations begin to multiply did not change with increasing deformation temperature, but the dislocation density required for plastic deformation to proceed decreased significantly with increasing deformation temperature up to 573K. Analysis using the Kocks & Mecking model showed that the temperature dependence of the dislocation multiplication rate was small, but the dynamic restoration rate increased monotonically with increasing temperature. Therefore, as the deformation temperature increased, dislocation annihilation due to dynamic recovery or recrystallization became dominant over dislocation multiplication, and the dislocation density decreased during plastic deformation.

The microstructure and mechanical properties of Ti-Al-Ni-Cu-Si alloys were evaluated, and the effects of the addition of Ni, Cu, and Si were investigated. Microstructural analysis revealed that the alloy consists of two phases: the α phase and the eutectoid phase, with the precipitation of Ti₂ (Ni, Cu) as an intermetallic compound (which is identified by SEM and TEM analyses). Tensile tests tested at various temperatures ranging from room temperature to 700°C showed that the Ti-Al-Ni-Cu-Si alloys such as Ti-3Al-0.5Ni-0.5Cu and Ti-3Al-0.5Ni-0.5Cu-0.3Si alloys (in mass%) exhibit a higher strength at room and intermediate temperatures (～500°C), and a lower stress at high temperatures ( ≥ 600°C) compared to conventional Ti-Al-V alloys having similar β phase stability. The results obtained in this study successfully suggest a new type of V-free Ti alloy with high strength from room temperature to 500°C and improved hot working ability (a low flow stress and a high elongation).

Porous aluminum is expected to be used in various industrial applications due to its low specific density and excellent shock absorption properties. Recently, roll forming has been investigated as a method of shaping porous aluminum. It has been found that the pore structures of porous aluminum are maintained by these processes on softened porous aluminum immediately after foaming. However, it is not clear whether the mechanical properties of the porous aluminum are retained after roll forming. In this study, we attempted to predict the compressive strength of roll formed porous aluminum X-ray CT images using a machine learning model trained on unformed porous aluminum. By this prediction, we examined whether roll formed porous aluminum and unformed porous aluminum exhibit similar compressive properties. As a result, it was found that the machine learning model trained on unformed porous aluminum could be used to predict the compressive strength of roll formed porous aluminum. The results also suggested that roll formed porous aluminum indicate the similar compressive properties to unformed porous aluminum.