The effects of thermally stabilized particles in Al–Mg–Si alloy on recrystallization behavior were investigated to obtain fundamental knowledge to control microstructure, texture and mechanical properties of this alloy. In this study, the Al–Mg–Si–Sc–Zr alloy was cast, homogenized and hot rolled. Three types of spherical Al₃(Sc, Zr) particles with L1₂ structure: rod-like incoherent, spherical semi-coherent and spherical incoherent particles were observed in the hot-rolled sample in the Al–Mg–Si–Sc–Zr alloy by using TEM, STEM and EDS. In addition, it was found that all particles have the core-shell structure with the core enriched with Sc and the shell enriched with Zr atoms by 3D-ET and STEM-EDS. It is considered that these particles are formed during casting, homogenized treatment and hot rolling. The results of crystal orientation distribution of annealed sample after cold rolling indicated that the presence of Al₃(Sc, Zr) particles may interfere with the recrystallization (the grain growth) until 600°C. From the comparison with the driving force of primary recrystallization and grain growth, and the pinning force of Al₃(Sc, Zr) particles, it was suggested that these particles mainly contribute to the suppression of grain growth. The results of in-situ heating SEM/EBSD analysis of cold rolled Al–Mg–Si–Sc–Zr alloy supported the suggestion.

This study investigated the low-temperature creep mechanisms in ultra-fine grained aluminum made by accumulative roll bonding. The low-temperature creep behaviors in ultra-fine grained aluminum with grain size of 0.39 µm were divided into four regions by three certain stress values, σ_my, σ_multi and σ_y. σ_my is stress for dislocation movement, σ_multi is stress for dislocation multiplication, and σ_y is yield stress. First, below σ_my, plastic deformation was negligible. Second, from σ_my to σ_multi, creep deformation with n=2.5 occurred by grain boundary sliding. Third, from σ_multi to σ_y, creep deformation with n=7.2 occurred by intragranular recovery of dislocations. Last, above σ_y, power-law breakdown was confirmed.

Microstructural evolution during region III deformation (T=723 K, ε̇=10⁻¹ s⁻¹) in a superplastic Al–Mg–Mn alloy (ALNOVI-U) was investigated. Surface makers drawn by focused ion beams (FIB) and internal observation by the electron back-scattered diffraction (EBSD) method were used for surface studies and internal studies, respectively. The surface markers clarified that both grain boundary sliding and dislocation activity significantly contributed for deformation. In the EBSD studies, formation of new low-angle boundaries (LABs) was observed at core/mantle boundaries and in core regions. The new LABs were formed by dynamic recovery of dislocation walls; it is the initial process of continuous dynamic recrystallization in region III superplasticity.

To predict hot tearing in direct chill (DC) casting and shape casting of aluminum alloys using thermal stress analysis, cooling rate dependence of viscoplastic properties in a partially solidified state is indispensable. Based on viscoplastic properties determined from experiments, this study develops a method to predict the temperature dependence of viscoplastic properties at an arbitrary cooling rate through the Clyne–Kurz microsegregation model. For validation of the developed method, tensile tests were performed on Al–5 mass%Mg alloy in a partially solidified state at three cooling rates. Results show good agreement between the predicted values and experimentally obtained values, which demonstrates that the developed method is effective for predicting the cooling rate dependence of viscoplastic properties.