Optimum laser irradiation conditions for densifying commercial-purity aluminum fabricated using selective laser melting (SLM) were studied using an SLM machine equipped with a 400 W Yb fiber laser. SLM specimens with a relative density of 99.7% could be obtained. The microstructures and the thermal and mechanical properties of dense SLM specimens fabricated under the optimum laser irradiation conditions were investigated. The as-fabricated SLM specimens showed granular microstructures of aluminum, silicon, and/or iron oxides dispersed finely (～0.3 µm) due to the rapid solidification by the laser irradiation. The mechanical properties were thus confirmed to be excellent (ultimate tensile strength, 110 MPa; yield strength, 90 MPa; breaking elongation, 30%). The thermal conductivity of the SLM specimen, meanwhile, was about 200 W/m·K, which was inferior to that of wrought commercial-purity aluminum (230 W/m·K). The effects of heat treatment (annealing) on the properties of the SLM specimens were also investigated. The thermal conductivity of an SLM specimen annealed at 450°C for 10 min increased to the same value as that of wrought commercial-purity aluminum, although the yield strength and breaking elongation were both slightly decreased.

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In this study, effects of heat-treatment temperature on microstructure, lattice parameters of martensite phase, and shape memory properties of Ti–4.5Al–3V–2Fe–2Mo alloy (SP-700) were investigated. The volume fraction of α phase decreased and therefore martensitic transformation temperatures increased with increasing heat-treatment temperature. Increasing heat-treatment temperature also changed the lattice parameters of α″ martensite phase but did not form α′ phase. The maximum calculated transformation strain was estimated in the specimen without α phase precipitation. Shape memory effect and superelasticity were confirmed at room temperature and subsequent heating in the heat-treated specimens. Comparing to the specimens in which stress-induced martensitic transformation occurred during loading, a smaller shape recovery strain was observed in a specimen deformed by the reorientation of martensite variants during heating. It was suggested that dislocations were easily introduced during the twinning deformation in the reorientation process because of large magnitudes of twinning shear of SP-700.

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The effects of Si content on recrystallization of 3003 aluminum alloys were investigated to obtain fundamental knowledge to control the mechanical properties of heat exchanger materials. The 3003 aluminum alloys containing various amounts of Si were cast, hot-rolled, cold-rolled and annealed at various temperatures. The recrystallization temperature became higher, and the decrease in the solid solute Mn content became larger with the decrease in the Si contents. When the annealing temperature was lower than the recrystallization temperature, minute dispersoids with the size of around 10 nm were observed in the alloy without Si addition, whereas they were not observed in the Si-added alloys. These results suggested that the recrystallization was strongly inhibited by the precipitation which was enhanced by nucleation around the dislocations during the annealing, if the Si content of the 3003 alloy was extremely low. The precipitation during the annealing was considered to be caused by the large amount of the solid solute Mn. Since the solid solute Mn was considered to be drastically decreased by the precipitation of Al–Mn–Si compounds during the hot-rolling process, the inhibition of recrystallization by the precipitation during the annealing did not occur under the high Si content.

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