Steam aging behavior of Al–Mg–Si alloys was investigated in order to clarify if steam could enable to induce precipitation. Age-hardening behavior was evaluated by Micro-Vickers hardness tests and differential scanning calorimetry (DSC). As a result of steam aging, that is an aging heat treatment utilizing thermal energy of steam, it was revealed that age hardening occurs in Al–Mg–Si alloys even in a steam atmosphere. When steam aging at 100°C was subjected to the alloys, the age hardening was suppressed compared to that of the alloys subjected to pre-aging at the same temperature, although the age hardening was superior to the alloys subjected to natural aging. On the other hand, it was clarified that superior age hardening was exhibited by subjecting to steam aging immediately after pre-aging at 100°C for 1.8 ks. Therefore, it was possible to induce age hardening by the thermal energy of steam, furthermore, an excellent age hardening could be raised via steam aging by appropriate thermal history based on the formation behavior of nanoclusters.

The obtained microstructures of a Ti–6Al–4V alloy welded by Linear Friction Welding (LFW) for the equiaxed- and the bimodal-(α+β) starting microstructures were investigated and evaluated quantitatively. The widths of center welded zone (CWZ) are 227 µm (for the equaxed starting specimen) and 396 µm (for the bimodal starting specimen), respectively. The microstructure at the joining interface for both starting microstructures exhibits the fine acicular (α+β) morphology, indicating that severe plastic deformation in β region is underwent at the joining interface and α′-martensitic transformation and subsequent decomposition to (α+β) occur during cooling process. Additionally, formation of the massive-α grains is also observed for the bimodal starting microstructure. Accompanied by this microstructural formation, the highest value of Vickers hardness is exhibited at the joining interface. Furthermore, this work also reveals the FEM result in which the behavior of continuous dynamic recrystallization of β phase is simulated.

The dislocation structure was analyzed in a Mg–4.98Al–1.46Ca (mass%) alloy using invisible criterion with transmission electron microscopy. Basal and non-basal segment of dislocation induced during die-casting is determined as much 〈a〉 and a few 〈a+c〉 dislocation. After the aging at 523 K for 10 h and tensile deformation at 473 K, only basal 〈a〉 dislocation can be observed. This dislocation structure is not observed in crept specimens, which support the difference in dominant strengthening mechanism between creep and tensile deformation.

In this study, the relationship between the drawing formability and texture of an Al–Mg–Si alloy with various rolling and heat treatment was investigated. The LDR (Limiting Drawing Ratio) value became highest only when the average r value was high and Δr was low. Randomization of texture by reducing the cube orientation density of the recrystallized texture is effective for improving draw formability. In order to obtain randomization of the final texture, it is important to randomize the initial orientation, to maintain proper solid solution and to form fine precipitates (clusters, acicular β″) in the middle of the process.