We investigated the corrosion resistance of Al–Mg(5052) alloys by means of the electro-chemical measurement, the immersion test and the observation of structures. The surface of alloys were modified by adding Cu with electronbeam melting method, and then coated with the oxide film contained Ge and Mo elements by three chemical treatments. The corrosion resistance of the alloy coated with the oxide film by immersing in the 4×10⁻³ kmol·m⁻³ Ce (CH₃CO₂)₃ boiling aqueous solution for 5.4 ks was improved more than by the other chemical treatments. The small Ge and Mo were in the oxide film and the distribution of these element is not uniform. Especially the concentrations of Ge and Mo were high in the vicinity of the intermetallic compound (Al₂Cu) . Micro voids and the other defects in the oxide films were increased with the increase in the intermetallic compound Al₂Cu existing as secondary phase, and those defects affected as a corrosion initiation.

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Yield stress anisotropy in 85% cold rolled and low temperature annealed sheets of Al–Mg alloys was studied from viewpoints of both texture and microstructure using X-ray diffraction, resistivity measurement and TEM. Texture analysis by X-ray diffraction suggests that the texture has little effect on the yield stress anisotropy of cold rolled and annealed sheets. In contrast, the result of resistivity suggests that the anisotropic arrangements of dislocation cell walls have a significant effect on the yield stress anisotropy. TEM observation shows that deformation zones developed around coarse particles have a random arrangement to the rolling direction and shear bands have geometrical arrangement to it. Further, they have considerably high dislocation density. It is concluded that these dense dislocation regions, which act as obstacles to slip, influence the yield stress anisotropy of cold rolled and annealed sheets.

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The isothermal dendritic growth process of an Al–Cu binary alloy was simulated by utilizing the phase-field method. The morphology forming process of the α phase of the aluminum rich Al–Cu system was clarified dynamically. Lower the growth temperature, faster the growth velocity of the dendrite primary arm and finer the dendrite structure. In addition, it was confirmed that the degree of segregation of Cu in dendrite arms became evident in increasing supercooling. The growth velocity of primary dendrite arm V can be expressed as a function of dimensionless supercooling Δ and Cu atomic concentration c such that V [× 10⁵ μm/s] = (1160–124c)Δ^2.45. The radius of the dendrite primary arm d does not depend on Cu atomic concentration c but on dimensionless supercooling Δ as d[μm]=0.0818Δ^−0.543. Dimensionless supersaturation Δ_c is a function of Peclet number P= (Vd/2D_L) such that Δ_c = 0.929 + 1.2002 (1⁄P)² -1.4128 (1⁄P).

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Behavior of microalloying elements in the early stage of phase decomposition of Al–Cu alloys has been extensively investigated using the electrical resistivity measurement, differential scanning calorimetry (DSC) and transmission electron microscopy. The microalloying element of Mg retards the initial phase decomposition and greatly accelerates the subsequent decomposition giving an increased resistivity maximum. The microalloying elements of Ag and Zn, on the other hand, have almost no effects on the decomposition of Al–Cu alloys. The combined additions of Mg and Ag markedly retard the phase decomposition in both the initial and subsequent stages. In order to elucidate the fundamental mechanisms of the microalloying effects in an atomic scale the Monte Carlo computer simulation was performed. In the simulation it was found that the element of Mg preferentially traps the quenched-in excess vacancies in the initial stage through so-called vacancy trapping mechanism. In the subsequent stage the characteristic complexes containing Cu, Mg and vacancies, i.e. Cu/Mg/vacancy complexes, are formed and they act as effective nucleation sites for GP zones.

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Acoustic emission (AE) behavior during tensile deformation and fracture was investigated for Al–Mg–Si base alloys with and without excess silicon. In as-quenched specimens, a peak of AE event counts was observed only at a yield point and then it reduced with increment in plastic strain. The AE activity at the yield point increased with the amount of silicon content. AE signals associated with yielding had mainly its amplitude ranges below 60dB. Change in root mean square (RMS) voltage with deformation well corresponds to that of the AE event counts. On the other hand, in the T6–aged specimen, the peak of AE counts appeared not only at the yield point but also at the occurrence of intergranular fracture. AE signals associated with the intergranular fracture had its amplitude ranges up to 100 dB. The change of RMS voltage revealed that high AE energy was released from the specimen when the intergranular fracture occurred.

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Influences of chemical compositions of base metal, temperature difference ΔT between liquidus and solidus, and arc time on the susceptibility of liquation cracking were studied using the Varestraint test on 6082 aluminum alloy which was GTA spot welded. A commercial 6082 alloy and seven kinds of experimental 6082 alloy whose magnesium, silicon and manganese contents were changed were used. The susceptibility of liquation cracking was evaluated from the maximum crack length observed in heat affected zone after the Varestraint test. Liquation cracking was observed along grain boudaries on which low melting point compounds (mainly Mg₂Si) were melted. The maximum crack length increased with arc time and ΔT. The addition of Si and Mg which increased ΔT promoted the liquation cracking, whereas the Mn addition suppressed the cracking by grain refining.

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