An eutectic Al-Si alloy melted at 800 °C and poured into a metallic mold. Cooling rate of the molten metal was varied according to the thickness of castings; 0.05, 0.09, 0.16, 0.35, 0.54, 2.42, and 3.38 mm. Microstructures of eutectic solidified regions were mainly observed by electron microscopy.
A plain bright area appeared in the eutectic region in the lower part of the specimen of 0.05 mm, where the cooling rate was at the highest. The cooling rate of the upper part of specimen was lower than that of the lower part. Many precipitated spots in the upper part were arranged in a dotted line on the grain boundary of primary α crystals. In the specimen of 0.09 mm, many precipitated spots appeared at random in the bright eutectic solidified area only. In the specimen of more than 0.16 mm in thickness, the bright area was changed to two phases, α and Si, which were entirely mixed each other. In the specimen of further more thickend, the growth of α phase of the eutectic region was more accelerated with the increase of thickness, and the grain boundary between primary crystals and α phase of eutectic region was observed more indistinctly in microstructure. Then, the microstructure of the specimen of 2.42 mm was very simple, in which large eutectic Si grains were scattered in the continuous α phase.
The change of microstructures was varied according to the quenching rate of molten metal even when the specimen was rapidly cooled.

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The purpose of this study was to obtain the basic data on distributions of residual stresses in various types of aluminum welded joints. In this paper, the effects of dimensions and heat input during welding operations on residual stress distributions of 5083-0 butt joints are discussed.
The residual stresses were calculated from the strains which still remained when the welded joint was cut into sections to release the stresses. The strains were measured by using resistance strain gages.
In conclusion, the following results were obtained:
(1) As general properties of residual stresses in welding, high tensile residual stresses having the magnitude nearly as large as the yield strength of the material appeared near the bead in the direction parallel to the weld line. However, the stresses normal to the weld line were smaller than those parallel to the line.
(2) The maximum value of tensile residual stress was related to the length of the welded joint, but not so much dependent on its width.
(3) Little effect of the heat input was given on residual stresses.

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This paper decribes the facts that aluminum alloys containing dispersed TiC were little strengthened with the increase of TiC contents up to 50%, however, they were very hardened by heat treatment.
For example, when the alloys were kept holding at 650°C, their values of hardness number were raised from Hv 60 (initial) to 110 (final) in 13% TiC alloy, from Hv 55 to 150 in 16% TiC alloy, and from Hv 80 to 610 in 50% TiC alloy.
The hardening phenomena may be due to the decomposition of TiC in aluminum by heat treatment for the formation of Al₃Ti and Al₄C₃. The grain size of Al₃Ti was about 10μ and that of Al₄C₃ was about 2 5 μ. These small particles were homogeneously dispersed in aluminum matrix.

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It was reported in the previous papers that crystal grains of MIG welds of aluminum alloys were refined and welding cracks were decreased by the addition of nitrogen to shield gas.
In this paper, effects of nitrogen addition to shield gas on mechanical properties and blowholes of welds are examined.
The following results were obtained.
(1) Nitrogen addition had no effects on mechanical properties of welds of 5083 alloy.
(2) Mechanical properties of Al-Zn-Mg alloys were improved by nitrogen addition.
(3) Inclusions formed in weld metal by nitrogen addition had little effects on its mechnical properties.
(4) Nitrogen in shield gas did not always decrease blowholes of welds, though it is reported to decrease the blowholes in some literature.

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In this paper, drilling machinability of aluminum-silicon binary alloys is discussed.
Factors and conditions of the experiments were as follows.
Five kinds of alloys were used for the speciments; their silicon contents were, 12, 16, 19, 22, and 25%, respectively. The tools used for experiments were 2 kinds of drills of the standard type, the diameters of which were 8 and 10 mm. Most of the thicknesses of specimens were 15mm for 10mm drill and 8, 12, 15, and 16mm for 8mm drill. Experiments were carried out under dry condition.
The results obtained by the experiments were as follows.
1. An approximately linear relation was found between the cutting force and the feed. It showed a tendency that the adhesion of chips to the drill and the generation of heat by the friction between material and tool were more violent with the less content of silicon in the material.
2. Burrs were more brittle and their mechanical strength was lower with the increase of silicon content in the material. Generally speaking, the burrs were easy to be removed.
3. The cutting force was increased in proportion to the thickness of specimen. This tendency was more evidently observed for the material of less silicon content.
4. The chips were brittle and likely to form fragments in the material of high silicon content. Whereas, in the material of low silicon content, they were so ductile and viscous that they often curled up around the drill.
5. The lowering of cutting efficiency of a tool after drilling many holes was more obviously observed in the material of less silicon content and for lower cutting speed.

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Ageing processes and age-hardening characteristics of Al-Ag-Cu ternary alloys were investigated by means of measuring hardness and specific heat. It was confirmed by measuring specific heat that two kinds of G. P. zones were formed on ageing at low temperatures; the one was rich in silver and the other was in copper. The formation of the former zones preceeded that of the latter. An intermediate phase predominantly precipitated on ageing above 190°C.
Marked hardenability on ageing was observed, which proved that Al-Ag-Cu alloys are one of the strongest Al-base alloys. Solid solution hardening behavior was also studied and it was concluded that this behaviour could not be explained only by the strain field produced by the solute atoms.

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