In the previous report, the contact potential differences of aluminum oxide films were investigated. This report deals with the relationship between the contact potential differences and the density of anodic aluminum oxide films. The following relationship was obtained between them;
ΔV = 32πeDc/ε×10-11{Δρ2-0.31Δρ/Δρ2-0.44Δρ+0.061}
Here, ΔV is the contact potential difference between aluminum and its oxide film, Δρ is the difference of the density between aluminum and its oxide film, ε is the dielectric constant of aluminum oxide film and D_c is impurity concentration of aluminum oxide film.

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Effects of Ca addition on grain size of primary silicon crystals in an Al-20%Si alloy were studied by means of an optical microscope and an X-ray microanalyzer. When a melt was held at 800°C, 0.13% Ca addition resulted in refinement of primary silicon and melts with 0.29-0.86%Ca additions did not resulted in microstructural refinement. White-colored particles were seen in the primary silicon crystal and eutectic structure in Ca-treated specimens and the composition of these particles approximated to CaAl₂Si₂ by microprobe analysis. The growth of primary silicon crystals in an Al-20%Si alloy treated with 0.13%Ca was interpreted in a manner similar to the twin reentrant mechanism reported by Hamilton et al for the case of germanium crystals growing in its melt.

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In Al-Cu-Cd alloys, Cd as an additional element would affect the secondary defect structure of Al-Cu binary alloys, and on the other hand, the Cd rich phase formed at the relatively early stage of aging. Therefore, the study on the precipitation behavior of the intermediate phase (θ') was carried out in Al-4wt%Cu-Cd alloy system with various Cd contents up to 0.114wt%, in relation to the defect structure and the Cd rich phase. Specimens were solution-treated at 520°C, quenched and finally aged at 200 and 250°C for various times.
The results obtained were as follows.
(1) The defect structure in this alloy system also consisted mainly of dislocation loops, which were finer and denser with increasing Cd content.
(2) The θ' precipitates first appeared on dislocation loops in ternary alloys as well as in the binary alloy. But in ternary alloys, θ' precipitated on Cd rich phase formed in the matrix, resulting in the denser distribution of θ' in ternaly alloys (with increasing Cd content) compared with that in the binary alloy.
(3) However, in ternary alloys, it was observed that Cd rich phase particles did not easily grow and only large ones were seen to act as the sites of θ' precipitate. The slow growth rate of those phases would explain the above fact that θ' precipitated preferentially on dislocation loops.
(4) These phenomena as to θ' precipitate in this alloy system were in contrast to those in Al-Cu-Sn alloy system, already reported by the authors. In other words, it would be clear that the aging rate at elevated temperature was lower in Al-Cu-Cd alloys than in Al-Cu-Sn alloys, in which all Sn rich phase particles were available for θ' precipitate with the disappearance of preferential precipitation of θ' on dislocation loops.
(5) The width of the precipitate free zone of θ' corresponded well with that of the loop free zone in the binary alloy, but not in ternary alloys since θ' formed on Cd rich phase particles within the loop free zone.

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The alternate bending tests were conducted on butt-welded specimens of 5083-0 aluminum alloy with thickness of 6mm having serious porosities as the weld defects. The porosity was artificially introduced into the welds by MIG welding using the excessively wet filler wire. The state of existing porosities was examined for all buttwelded specimens by radiography.
The principal results observed were as follows.
1) The fatigue fracture of butt-welded specimens with reinforcement occurred at the weld toe even though the specimens contained remarkable porosities. The presence of porosities in the weld does not affect the fatigue strength in the as-welded condition.
2) The fatigue strength of specimens containing serious porosities, but having the small reinforcement angle by machining the deposite metal near the weld toe, was slightly greater than that of the defect-free specimens. The fatigue strength in the as-welded condition is more affected by the reinforcement shape than by the porosities.
3) In the case of the butt-welded specimen with the reinforcement machined flush, considerable decrease of the fatigue strength resulted from the existence of serious porosities.

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A kinematically admissible velocity field was assumed to describe the flow in axisymmetric indirect extrusion. The deforming zone is bounded by two spherical surfaces of velocity discontinuity, of radius R₀ and R_f with their centers at a⋅R₀ and a⋅Rτ from the apex of the cone of the die. The flow in the deforming zone is directcd toward the apex of the cone. And an upper bound approach was applied in order to obtain the necessary informations about the deformation process; the extrusion pressure, shape of the deforming zone, the distored grid pattern and the effective strain distribution. The analytical results for axisymmetric indirect extrusion through a flat die with different extrusion ratios and friction conditions were compared with those obtained experimentally, and an excellent agreement was found.

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