The solution treatments at relatively higher temperatures promoted the spherodization of eutectic silicon and the consequent improvement of 0.2% proof stress and tensile strength. The elongation and absorbed energies fell with the solution treatment time. The largest tensile strength and proof stress were obtained in the aging time range between 720 and 1080ks when the aging temperature was 418K. The mechanical properties of AC4CH were proved to be attributable to the spherodization and the coalescence of eutectic silicon in the solution treatment at higher temperature for shorter time.

View full abstract

The pitting-attack behavior have been investigated on Al-0.9%Zn alloy specimen, which is galvanically coupled to titanium in 0.1M NaCl solution. Pitting-attack is found to occur not in deaerated environment but in aerated one. It is shown that pitting-attacks occur only when f^Al_pit_??_1, where the pitting occurrence factor f^Al_pit can be calculated from the data on rest potentials of cathode, rest potentials of anode, galvanically coupled potential of anode and pitting potential.

View full abstract

Strength and SCC resistance of RRA-treated 7050 aluminum alloy were investigated, compared with the alloy conven-tional-treated. Over-aging treatments such as T76 and T73 were effective for the improvement of SCC resistance, but a certain loss in strength was unavoidable. The RRA-treatment for 7050 alloy improved the SCC resistance up to the level compared to that of T73. Far from decreasing, the strength of RRA-treated alloy increased slightly, compared with T6. The strength obtained in T6 treatment and the SCC resistance in T73, therefore, can completely coexist in the case of RRA-treated alloy. This special effectiveness for the 7050 alloy was considered to result from homogeneity in the precipitation structure of 7050 alloy, probably induced by the zirconium addition in 7050 alloy.

View full abstract

Non or 45° earing is commonly observed in a 3004 alloy annealed at higher temperatures than 400°C by rapid heating using such as CAL (continuous annealing line). In the present work, it has been recognized that 0-90° earing can be developed by partial or full recrystallization annealing at the temperature range of 315°C to 370°C even with the rapid heating prior to higher temperature annealing. These procedures may be effective for the reduction of earing of can body materials. The earing behavior mentioned above is consistent with the development of the textures during annealing, which was investigated by X-ray analyses and TEM observations.

View full abstract

The cathodic processes localized to iron rich intermetallic phases on commercial aluminum alloys during corrosion in neutral chloride environments are controlled by the structural and compositional changes occurring on these phases in a locally stable alkaline environment. These phenomena are investigated by conventional electrochemical techniques on synthetically grown Al₃Fe crystals. The surface of the crystals is enriched by metallic iron at E<-1.175 V_SCE as a result of selective aluminum dissolution. In the potential range -1.175<E<-0.72 V_SCE, the surface is essentially passive to oxidation resulting from the successive formation of an adsorbed FeOH and the bulk oxides Fe(OH)₂ and Fe₃O₄ with increasing potential. In the range -0.72<E<-0.66 V_SCE, a transpassive behavior is observed, characterized by the selective dissolution of aluminum and oxidation of enriched iron into an unprotective oxide, possibly FeOOH. At higher potentials, the surface passivates again by Fe₂O₃ formation. The significance of these results on aluminum alloy corrosion is discussed. In addition to their role as cathodes, it is argued that these compounds may be contributing directly to pit initiation and the determination of the pitting potential on aluminum alloys.

View full abstract

The age hardening behavior of SiC_w/Al-2.3mass%Li-2.8mass%Cu alloy composites fabricated by the squeeze casting method was investigated using micro Vickers hardness, calorimetric technique and TEM observation. The composites showed remarkable age hardening, and the age hardening of the composites was more accelerated with increasing SiC whisker volume fraction. The composites aged at 423K showed a hardness increase of two stages, while the unreinforced matrix alloy showed a monotonous hardness increase. It was clarified that the first stage of hardness increase of the composite was due to the precipitatign of δ' (Al₃Li) phase and the second one was mainly due to the precipitation of T₁ (Al₂CuLi) phase. In composites, the T₁ phase precipitates became dominant with increasing SiC whisker volume fraction and controlled the age-hardening rate at 423K, because the T₁ (Al₂CuLi) phase precipitated preferentially on dislocations generated during quenching after the solution treatment due to the difference in the thermal expansion coefficient between the SiC whisker and matrix.

View full abstract