Some studies have been reported on black spots which appear on 6063 extruded alloys anodized in a sulfuric acid solution. It has been confirmed that black spot formation is induced by holding the alloys for a certain time interval at 300-400°C after direct quench from a solution temperature. However, in a practical extrusion process where forced air cooling is applied, materials do not remain at about 300°C for several minutes. In the present research, a cause for black spot formation was studied with continuous measurement of a cooling process after extrusion. It was found that black spots were not induced only by such a simple cooling condition as air or slow cooling.
Parts of the extuded materials were rapidly cooled when they were transferred on the run-out-table and, thus, contacted the carbon plates. However, the same parts were found to be reheatecl upon removal from the carbon plates. The materials subjected to such rapid cooling and rehearing developed black spots after anodic oxidation, even when reheating time Twas short. In order to study a precipitation rate in rapid. cooling and reheating, the C curves, isothermal aging curves, were obtained both at normal isothermal aging and at reheating after rapid cooling by measuring changes of electrical conductivity. It was found that rapid cooling accelerated the aging process remarkably and produced higher conductivity and lower hardness upon tempering. The above experimental observation favourably explains the phenomena associated with the black spot formation occuring in an indtistrial process.

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6063 alloys with various compositions were extruded at various temperatures under fast and slow extrusion rates. Textures and mechanical properties of the extruded and the annealed rods were examined. The following results were obtained
(1) The higher temperatures extrusion, the addition of the larger amount of Mg and Si, and the faster extrusion rate improved the mechanical properties of the extruded 6063 alloys. The excellent strength was obtained when the alloys with more than 0.45%Mg and 0.3%Si were extruded at temperatures higher than 480°C.
(2) The slow rate extrusion produced the duplex textures; i.e., strong <111> + weak <100> at low temperaturessand weak <111> + strong <100> at high temperatures. However, when the extrusion was performed under the fast rate, the wide and intense zone to indicate the <100> texture developed in the {111} pole figure. It was found that the ratio of the intensity of the <100> texture to that of <111> texture was increased as the extrusion temperature and the extrusion rate as well as the content of Mg₂Si increased.

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Effects of cutting fluids on tool wear, surface roughness and cutting force in machining of hyper eutectic Al-Si alloy with a carbide tool bit of K10 were studicd. Sevcral kinds of commercial cutting fluids such as compound oil, E. P. oil, soluble oil and light oil were used. The cutting fluids were supplied from the top surface of the rake at rates of 3.5-6.5l/min with use of an oil pump. The results obtained are as follows: The effect of the fluid on decrease of flank wear depended on the cutting speed, but was clearly noted even at such high speed cutting as that of 300m/min. For cutting faster than 200m/min, the soluble oil was most effective, while for lower speed cutting the light oil as well as the E . P. oil of low viscosity was desirable. The effect of the cutting fluid on surface roughness became less pronounced as the rake angle and the cutting speed were increased. However, it was found that the neat cutting oil and light oil were preferable to produce good surface finish. The smaller cutting fcrce was required when a tool with a smaller rake angle and the soluble and the light oil were used.

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In order to know the correlation between the stress corrosion racking and the internal friction which is sensitive to structural changes, the internal friction has been measured in an Al-Zn-Mg alloy which is easily subjected to stress corrosion cracking. The natural decay of the transverse resonance vibration was utilized to measure the internal friction of specimens after stress corrosion tests in an aqueous solution (CrO₃ 70g/l, NaCl 30g/l and K₂Cr₂O₇ 60g/l) under tensile stress of 98% of yield strength. Results obtained are as follows:
(1) When the amplitude independent internal friction began to increase, the stress corrosion cracking was not detected by an optical microscope. This observation indicates that plastic deformation occurs.
(2) The harder the yield stress was, the earlier occurred the stress corrosion cracking.

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Effect of heat treated oil, existing on the surface of aluminum, on the adhesion of polyethylene to aluminum was investigated. The results obtained are as follows:
(1) The oil on the aluminum surface was removed abruptly when it was heated at 200°C for 5hrs or at 300°C for 5hrs.However, complete oil removal was possibly by heating at 400°C for more than 5hrs.
(2) The peeling strength of aluminum, covered by oil was decreased monotonously with the heat treatment, while that of aluminum covered by oil was decreased in an irregular manner with the heat treatment. The decreasing rate of the peeling strength was slower in the case of aluminum covered by oil.
(3) Aluminum surfaces contaminated by polar oleic acid or butylstcarate had a larger peeling strength and showed slower decrease of the strength upon heat treatment than those contaminated by non-polar liquid paraffin.
(4) In aluminum-polyethylene laminated systems, cohesion failure occurred in the polyethylene layer or in the oil layer, depending on the condition of remaining oil on the aluminum surface.

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