The fatigue crack propagation behavior has been investigated under tension-tension cyclic stress in air, distilled water and 3 mass% NaCl aqueous solution for 5052-H34 aluminum alloy sheet with a small blind hole as an artificial surface defect. The relationship between the maximum nominal stress &simga;_max and the number of cycle to failure (fatigue life) N_f is expressed as σ_maxⁿN_f=C, where n is the stress exponent and C is constant. In 3% NaCl aqueous solution, the fatigue life and the stress exponent become lower than those in other environments and corrosion environment becomes dominant factor, as a result, fatigue cracks initiate and propagate irrespective of surface defects. The crack propagation rate in 3% NaCl aqueous solution is higher in the early stage of fatigue crack propagation than that in air, but in the later stage, the difference between the crack propagation rates in air and in 3% NaCl aqueous solution is not clear. In addition, the surface crack propagation rate is accelerated due to the corrosion effects in 3% NaCl aqueous solution, resulting in the flatter shape of crack front compared with those in air and distilled water.

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Age-hardening and precipitation behavior of an Al–2.5 mass%Cu–0.23 mass%Sc alloy were investigated by means of hardeness test and TEM observation. The effect of scandium on the age-hardening behavior of the Al–Cu alloy is most remarkable at the aging temperature of 573 K. Precipitates formed at 573 and 623 K in the Al–Cu–Sc alloy are the θ′–Al₂Cu and Al₃Sc phases. They precipitate independently in the matrix without any apparent interactions for the heterogeneous precipitation.

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Aluminum-borate whisker and alumina short fiber reinforced AC4B aluminum composites were fabricated by squeeze casting and its mechanical and wear properties were evaluated. Tensile strength of 20V_f% aluminum-borate composite is about 450 MPa at room temperature. That of hybrid composites of aluminum-borate whisker and alumina short fiber is slightly lower than that of the 100% aluminum-borate whisker composite, but higher than that of the matrix alloy. Wear loss of hybrid composite contain 16V_f% aluminum-borate whisker and 4V_f% alumina short fiber was apporoximately 20% smaller compared with composite of only aluminum-borate whisker. In accordance with modified Kelly-Tyson's equation, tensile strength of composite was evaluated and it was found out that the experimental values were around 60~80 percent of the calculated values.

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Electrochemical measurements were carried out to investigate the effect of heat treatment after brazing on the selective dissolution characteristics of Al–Si alloy brazing filler. Pitting potential of primary α phase was more noble than that of eutectic after brazing, resulting in the selective dissolution of eutectic phase in the filler. Pitting potential of the filler, both eutectic and primary α, varied to less noble one during reheating at 200~400°C after brazing, due to the decrease in solute silicon in the filler. After the heat treatment for more than a temperature dependent critical time (t_c), pitting potential both for eutectic and primary α ceased to vary. The time t_c was longer for primary α than for eutectic. No selective dissolution of Al–9% Si brazing filler occurred, when it was heated for the time longer than t_c for primary α.

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The composites with the characteristic structures have been obtained by squeeze casting employing TiO₂ reinforcement and aluminum, which are composed of the reaction products (Al₃Ti, Al₂O₃), sintering of TiO₂ phase due to the reaction between anatase type TiO₂ and matrix aluminum. The structure and the formation process were discussed and some properties of the composites were investigated. The experimental observation proved that the reacted structure of the composites were formed through over 2 steps reactions at least. The hardness of the phase varied largely about HV40 to HV1350 depending on the microstructure. While the bending strength of the composites indicated low values as 107 to 117 MPa due to heterogeneous structure, the wear resistance of the composites were considerablly superior to their matrix alloys (AC4C, AC8A) or cast iron (FC25).

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