Lithium chloride was electrolyzed at 700°C with a cathode of molten aluminum or molten Al-Cu-Mg-Zr alloy in a ceramic fiber contained permeated with molten lithium chloride-potassium chloride electrolyte. Electrodeposited lithium alloyed directly with the molten aluminum or molten Al-Cu-Mg-Zr alloy. Current efficiency of alloyed lithium is over ninety per cent in wide range of current density. Over current density limit, potassium deposits at the cathode, and doesn't alloy over 10ppm with aluminum. Sodium containing in electrolyte as much as 1500-2000ppm doesn't alloy over 10ppm. The mechanical properties of Al-Li-Cu-Mg-Zr alloy produced by this process were also studied.

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RI-ITMT method was applied to improve the toughness of Al-Li system alloy. This method was found to be effective for the improvement of the toughness of Al-Li system alloy. The significantly finer grains were obtained by RI-ITMT method. However, the greatest toughness was not necessarily obtained in the finest grain size. The improvement in toughness was achieved in the specimens in which the second phase particles precipitated during overaging treatment in thermomechanical treatment process had remained after the final solid solution and aging treatment. Therefore, the improvement in toughness was achieved by preventing the stress concentration to the grain boundary, caused by the large planner slip, by the introduction of the second phase particles in addition to grain refinement. In addition to the Al₃Zr precipitate, Cu-rich precipitate also formed duplex phase with δ' precipitate. The heat treatment in Ar atmosphere was more effective in preventing the phenomenon of Li loss. However, it was impossible to prevent Li loss completely. Under the dynamic loading condition toughness increased due to the shear-lip associated with Li lost layer.

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Precipitation phenomena and mechanical properties in an Al-Li-Cu-Mg-Zr alloy were investigated by hardness measurements, tensile test, specific heat measurements and electron microscopy.
Hardness increased gradually but monotonously with aging time at room temperature and 323K, and increased remarkably at 373-473K. The rate of age hardening in this alloy was extremely larger than that for an Al-Li binary alloy. Various reactions of heat evolution and absorption were observed in the specific heat curves and were suggested to originate from the structural changes such as the precursory structure of δ', δ', T₁ and S' phases. The δ' phase contributed most to the increase in the mechanical strength.
Typical serrations were observed in the stress-strain curves for the under-aged specimens, while no serrations for the over-aged ones. Fracture surface structures revealed the morphology of a grain boundary fracture, and were more rugged for the specimens with higher strength.

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An investigation has been made on the effect of up to 2.3wt.% lithium addition on the elevated temperature properties of the well known heat resisting aluminum alloy 2219 (Al-6.3Cu-0.3Mn-0.18Zr-0.10V-0.06Ti). An addition of 1wt.% lithium decreased the alloy density by 3% and increased Young's modulus by 5.4%. The yield stress of 2219 alloy at room temperature and at up to 250°C increased with increasing lithium content, but no effect was observed at 300°C. Creep tests were performed in the range 200-300°C, under various loads. Indications were that the creep resistance at 200°C increased with lithium contents although that at 250° and 300°C was degraded by the addition of 2.3wt.% lithium.

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Tensile tests were carried out in an Al-Li-Cu-Mg-Zr alloy aged at 453K. The proof stress showed a positive dependence on the test-temperature near room temperature. The dependence is resulted from the fine and spherical δ' precipitates. Elongation at 77K lowered with the aging period. The values of elongation in the specimen showing the maximum bardness were less than 10%at 373K. Many cracks at grain boundaries were observed in those specimens showed such low ductility. The low ductility may be attributable to the lower work-hardening and the stress concentration to the grain boundaries, which were brought by localized dislocation motion on a few slip planes due to the δ' phase. At higher temperatures than 373K, elongation increased with an increase in the test-temperature. Grain boundary sliding takes place characteristically during deformation at 573K and over. It is considered that these elongation are resulted from the deformation like as the fine-grain superplasticity because the grain boundary sliding may cause higher strain rate sensitivity of flow stress.

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Superplastic behaviors of an Al-Li-Cu-Mg-Zr alloy for aerospace application have been investigated over the temperature range 600-800K and the initial strain rate range 1×10^-4-1×10^-2s^-1. In cold-rolled and annealed sheet specimens having fine and equiaxed grains of about 5μm diameter, superplasticity was observed above 725K, wherein the maximum elongation of 480% appeared and the strain rate sensitivity was determined to be 0.45 at 800K. As-rolled sheet specimens became much more superplastic than annealed ones, when holding time prior to the tensile test was chosen appropriately. No improvement in ductility was found in the temperature increasing tensile tests. Extruded specimens having fine but elongated grain structure did hot show superplasticity at all, probably because grain boundary sliding was suppressed due to a geometrical reason.

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The precipitation process in Al-2.3wt.%Li-2.3wt.%Mg alloy has been studied by means of differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). It has been found that the precipitation sequence in this alloy is as follows; supersaturated solid solution→pre-precipitate δ"→metastable δ' phase→equilibrium δ and T phases. The exotherms corresponding to the precipitation of the δ', δ and T phases and the endotherms to the dissolution of the δ", δ', δ and T phases respectively have been observed in DSC curves. It has been shown that the δ" is formed almost simultaneously with the δ' phase during quenching from the solid solution temperature and they coexist during ageing. The activation energy for the precipitation of the δ' phase determined by the analyses of the exotherm Q depends upon quenching or cooling rate and ageing temperature, while the activation energy for the dissolution of δ" determined by the endotherm P does not depend upon the quenching or cooling rate. This suggests that the precipitation rate of the δ' phase is accelerated by the quenched-in excess vacancies. The present results suggest also that the nuclei of the δ' phase tend to be formed by the homogeneous nucleation in the matrix.

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