Castings in plate form of commercially pure titanium KS50 and three titanium alloys, Ti-5Al-2.5Sn, Ti-6Al-4V, Ti-15Mo-5Zr, were prepared by using graphite molds and an arc skull furnace which was of tilting pour type with consumable electrodes, as previously reported. Mechanical and corrosion resistant properties of these castings were studied and compared with those of forged materials. In the case of KS50 and the α alloy, Ti-5Al-2.5Sn, there was no significant difference ofmechanical properties between the as-cast and the annealed castings. However, the strength of the α + β alloy, Ti-6Al-4V, in which phase stabilization occured during annealing, was increased by annealing. The hardening and the reduction of ductility due to ω phase formation in the Ti-15Mo-5Zr alloy castings were suppressed by annealing. There was no large difference of mechanical properties between castings and forgings of KS50. However, the Ti-5Al-2.5Sn alloy castings showed significant decrease of strength, compared to the forged materials, while the Ti-6Al-4V alloy castings showed slight decrease of strength and large reduction of ductility. The inferior properties of the castings seemed to be due to the large grain size. The presence of pin holes in castings of 0.5mm in diameter had a negligibly small effect on the tensile and smooth rupture properties. Annealing of the KS50 and the Ti-15Mo-5Zr alloy castings showed a small effect on the corrosion resistant properties which were, thus, comparable to those of the forged materials. α precipitates due to dendritic micro-segregation were observed in the Ti-15Mo-5Zr alloy castings and were not eliminated by the annealing treatment.

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Structural changes during aging of an Al-0.22wt% Zr alloy at 350, 400 and 450°C for 8-10000 hours were studied by means of optical and electron microscopes. In the initial stage of aging, dendritic or rodshaped precipitates were formed behind moving boundaries. Growth of these precipitates due to a grain boundary reaction was retarded by development of precipitation within grains. The dentritic or rod-shaped precipitates had an ordered cubic crystal structure of L1₂ type, a metastable Al₃Zr which did not change during the aging interval employed in the present study.
Precipitation of the equilibrium phase of Al₃Zr with ordered tetragonal structure of DO₂₃ type was also found at grain boundaries by prolonged aging. A new orientation relationship between the equilibrium Al₃Zr phase and the matrix was established.
Coherent spherical particles were also observed within grains. The particles were round to nucleate homogeneously at 350°C. However, at higher temperature aging, they showed tendency to nucleate preferentially at dislocations or original grain boundaries. Growth of these precipitates by prolonged aging accompanied loss of coherency and occurred preferentially along the <100> and <100> matrix directions, resulting in fobrmation of protrusions. It was found that these precipitate were Al₃Zr with L1₂ type structure. Plate like coherent precipitates, elongating along the <100> matrix directions, were sparsely observed within grains. These precipitates grew large and lost coherency with the matrix by generations of interfacial dislocations around them.

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Phase diagrams in the Al-rich side of solid state Al-Mg-Cr and Al-Mg-Mn alloys were reconfirmed. In addition, crystal structures of ternary compounds in these alloys were studied by an X-ray analysis with Cu-Kα radiation. Following results were obtained:
(1) In the Al-rich side of the Al-Mg-Cr system, the α solid solution, θ (CrAl₇), β (Mg₂Al₃) and the ternary compound E were identified. The shape of the phase diagram was almost the same as that previously reported. However, it was found that the solid solubility of Cr in Al was reduced as the Mg content increased.
(2) In the Al-rich side of the Al-Mg-Mn system, the α solid solution, MnAl₆, β (Mg₂Al₃) and the ternary compound T were identified. The shape of the phase diagram was nearly the same as that previously reported, except the region of (α + T). This region existed at the lower Mg content side as a whole.
(3) A complete analysis of the crystal structure of the E phase was difficult because satisfactory electrolytic separation of the compounds was not possible. However, it was fbund that the diffraction intensities of the E phase in the present study was satisfactorily explained by the parameters given by S. Samson. Thus, it was confirmed that the E phase was face centered cubic with the space group Fd3m, had the basic composition of Mg₃Cr₂Al₁₈ and had the Iattice parameter of 14.545±0.001Å.
(4) It was found that the diffraction pattern of the T phase was very similar to that of the E phase. Since this fact suggested that the T phase had the same structure as the E phase, the computation based on the parameter of the E phase was performed. The computed diffraction intensity was in close agreement with the observed value. Thus, it was concluded that the T phase was also face centered cubic with the space group Fd3m and had the basic composition of Mg₃Mn₂Al₁₈. The lattice parameter was 14.529±0.001Å.

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Effects of small additions of Fe, Si, Cu, Mn, Cr, Ti, Zr and Ag on stress corrosion cracking in the LT-direction and shear cracking of Al-Zn-Mg alloys were investigated with a special consideration of grain shape.
(1) Additions of Si, Cu, and Ag increased stress corrosion resistance in both LT- and ST-directions, while Mn, Cr and Zr additions increased stress corrosion resistance in the LT-direction but decreased that in the ST-direction. Effects of Fe and Ti additions on stress corrosion resistance were small.
(2) It was found that Fe, Mn, Cr, Ti and Zr additions affected stress corrosion resistance only through their effect on grain shape. However, additions of Si, Cu and Ag increased stress corrosion resistance through some other effects than that on grain shape. It was considered that a Si addition was effective through reduction of solute concentrations and Cu and Ag additions were effective by introducing changes in electrochemical properties of grain boundary regions.
(3) Effects of Fe, Si and Cu additions on shear cracking had the same tendency as that on stress corrosion cracking in the ST-direction. However, effects of Cr, Mn and Zr additions on shear cracking corresponded to that on stress corrosion resistance in the LT-direction rather than in the ST-direction. These observations were explained by occurrence of metal flow due to shearing and existence of directionality of stress corrosion resistance.

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Grain refinement by Ti in unidirectionally solidified aluminum alloys were studied under the condition to suppress crystal multiplication. Alloys with different Cu and Ti contents were unidirectionally grown from melts at a constant rate by using seeds of pure aluminum single crystals, and the number of grains was examined. The results obtained are as follows
(1) When the alloys were Ti-free, single crystals were grown from the seeds with the <100> direction, the prefered orientation in dendritic growth. When Ti was added to the alloys, growth of the crystals formed from the seeds was hindered by many newly crystallized grains at the growing interface.
(2) As the Ti content and the solidifying rate increased, the number of the grains increased.
(3) Grain refinement effect of Ti was suppressed when the melt was superheated. However, when both Ti and B were present in the melt, the grain refinement was still observed.
(4) Grain refinement action of Ti was not affected by types of solid-liquid interface morphology which depended on the Cu contents.
(5) Smaller grains were formed near the surfaces, when the alloy contained Ti.
(6) When 0.05%Ti was added to the Al-CuAl₂ and Al-NiAl₃ eutectic alloys, the solidifying interface took the cellullar structure. However, grain refinement effect of Ti was not observed in these eutectic alloys.
These results were considered to clarify heterogeneous nucleation due to a Ti compound when the Ti containing alloys were solidified in the absence of crystal multiplication. The mechanism to explain the grain refinement effect by such a Ti compound was also discussed.

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