The crystal structure and preferential orientation relationship with the matrix of grain boundary precipitates in a Al-1 mass%Mg₂Si alloy containing excess magnesium was investigated using transmission electron microscopy. A small number of equilibrium phases precipitated on a grain boundary at relatively high aging temperature. The equilibrium precipitates have some preferential orientation relationship with the matrix. At a peak aging condition where the intergranular fracture occurs, the diffraction pattern of a hexagonal system is obtained from the grain boundary precipitates. These precipitates are considered as an intermediate phase. The grain boundary precipitates have a preferential orientation relationship with the matrix as{001}_m_?_?{0001}_p. No equilibrium precipitate is observed at grain boundaries. The number of grain boundary precipitates decreases with increasing misorientation between two grain boundaries. The mean size of grain boundary precipitates increases with increasing misorientation.

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Rapidly solidified flakes of Al-10mass%Ce based alloys with additions of Fe, Mn, Cr, Ni or Si were prepared by atomizing and subsequent splat quenching onto a water-cooled copper roll. Consolidation of the flakes was done by cold pressing, vacuum degassing and hot extrusion. Metallography and constituent phases of the flakes and P/M materials were examined. Mechanical properties of the as-extruded P/M materials were examined by tensile tests at room and elevated temperatures. Formation of the primary crystals of the additional element compounds is suppressed at high cooling rate. The microstructures of the as-extruded P/M materials consist of fine intermetallic compounds with the size of˜0.1μm dispersed in the matrix. No change in hardness is observed for both the flakes and P/M materials isochronally annealed at temperatures below 573K. The microstructures of flakes and P/M materials exhibited high thermal stability against annealing at temperatures below 573K. The tensile strength of the P/M materials is higher than 350MPa with elongation higher than 15% at room temperature. Among the alloys, the Fe-bearing alloy has the highest tensile strength of 445MPa at room temperature, 346MPa at 473K and 216 MPa at 573K. The material with addition of Si has the lowest strength at all temperatures.

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The corrosion rate of 99.99mass% aluminum cold-rolled by a constant reduction rate (10% per pass) or a constant reduction amount (10% of original thickness per pass)method were measured in a 0.5mol/l-NaOH solution at 40°C. The changes in corrosion rate with the total reduction 0-90% corresponded very well to the changes in residual stress of the samples. For the sheets rolled by the constant rate method, the corrosion rate and the residual stress showed the maxima at 30% and 80%, and showed the minimum at 50% total reduction. In the case of constant amount rolling, both showed the maximum only at 30% total reduction. Both properties remained almost constant independently of total reduction after the recovery treatment at 100°C for 3h. These behaviors mean that the residual stress induced by rolling is a controlling factor in corrosion. Effects of pass programs, surface contamination and damage were also examined.

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The dispersion behavior and the interfacial reaction of various carbide particles in pure aluminum matrix composites made by a melt stirring method were observed and mechanical properties of TiC particulate aluminum matrix composites were also measured. WC particles decompose completely in molten pure aluminum during the stirring. Although NbC and VC particles can be incorporated into molten Al-1mass%Mg alloy, most of them decompose. Among various carbide particles, TaC, ZrC and TiC particles show high stability and uniform distribution, even though minute amounts of Al₃Zr and Al₃Ti are observed in the ZrC/Al and TiC/Al systems, respectively. The effect of processing temperature on mechanical properties of TiC/Al composites was evaluated. The properties are rarely affected by the processing temperature when the temperature is ranging from 1073K to 1273K. The strength of TiC/Al-Mg (Mg: 1-5mass%) composites is higher than that of a TiC/pure Al composite. The increment in strength by dispersing TiC particles becomes smaller with an increase in the strength of the matrix alloy for TiC/Al- (Cu, 5mass%Cu-Mg) composites. The strength increases and the elongation decreases with increasing volume fraction of TiC particles up to 17vol%.

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Precipitation behavior of Al-2.0mass%Li-0.2mass%Si and Al-0.8mass%Li-0.5mass%Si ternary alloys has been investigated mainly by means of micro-Vickers hardness measurements and transmission electron microscopy. Aging treatments were performed at constant temperatures in the range of 328 to 573K. Age hardening occurs at all temperatures. The precipitation of both the δ' (Al₃Li) phase and fine equilibrium (AlLiSi: T) phase contributes to the hardness increase. The shape of the T phase is rod-like at the early stage of aging and changes to plate-like with prolonged aging time. The orientation relationship between the matrix (α) and T phase is as follows:
(001)_α//(110)_T, [100]α//[001]_T.

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In order to develop a lower melting temperature filler alloy for brazing of aluminum alloy with high strength and low melting temperature, the eutectic compositions and temperatures of Al-Si-Zn system were determined by the thermal analysis. A typical eutectic composition was Al-4.2mass%Si-40mass%Zn, and the eutectic temperature was 808K. Spreadability of this eutectic alloy on 3003 alloy sheet coated with chloride flux was sufficient at 838K. Brazeability test was carried out with T-joint specimen in which brazing sheet was prepared by hot dipping. In the brazing of 3003/3003 and 3003/Al-5.5mass%Mg alloy pairs, flow of the filler metal was good and the fillet was satisfactory. On the other hand, in the case of Al-5.5mass%Mg/Al-5.5mass%Mg, no fillet formation occurred.

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Preferred precipitation of the η phase on dispersoids was examined in the 7075, 7050 alloys and 7075 (Zr) alloy containing Zr instead of Cr under the conventional overaged temper. Specimens were solution treated at 470°C, preaged at 120°C for 86.4ks and finally aged at (163-170)°C. The η precipitates nucleate on incoherent dispersoid of the E (Al₁₈ Cr₂Mg₃) phase inside the grain of the 7075 alloy. This causes serious loss of strength during overaging. Coherent dispersoids of the Al₃Zr phase do not act as the nucleation site for η precipitates in the 7050. Therefore, η precipitates appeare only on grain boundaries in the 7050 alloy. The substitution of Cr by Zr in 7075 alloy is found to improve the strength after the conventional overaged temper.

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