Dissolution behavior of Al-Fe-Si alloys with various Fe/Si ratio have been investigated in a 5% NaOH solution. Weight loss of the alloys decreases with decreasing Fe/Si ratio in the alloys. Dissolution process under the NaOH etching treatment is controlled by the cathodic reaction of water reduction. It is electrochemically found that the intermetallic compounds with lower Fe/Si ratio in the Al-Fe-Si alloys cathodically plays poor role in the etching process.

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Friction welding of a 6061 aluminum alloy to a S45C carbon steel was carried out using the insert metal of a 1050 aluminum. Optimum thickness of the insert metal, friction pressure, forge pressure, friction time and rotational speed of welding conditions were determined as 4mm, 90MPa, 300MPa, 1.2s and 2250rpm, respectively. When the insert metal turned into a thin (20-30μm) and homogeneous layer at the weld interface, the maximum joint efficiency of tensile strength was obtained and was about 95%. Successful welds were obtained by taking each optimum welding condition even if the thickness of the insert metal was varied from 2 to 6mm.

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The objective of this study is to clarify the behavior of hydrogen in an aluminum alloy from microscopic standpoint. The material used was Al-8%Mg alloy which was annealed and cold worked 5% or 20%. Besides tensile tests internal friction measurement, SEM and TEM observation were used to clarify the behavior of hydrogen. In internal friction measurements of the cold worked specimens after hydrogen charging, the increase of background and a new peak were observed. This shows the interaction of hydrogen atoms with dislocations, and the peak can be attributed to the drag of hydrogen by dislocation motion. In cold worked specimens, after hydrogen absorption, hydrogen atoms have interaction with dislocation and as the results, uniform ductility decreases and intergranular fracture is observed. From the coincidence between the work hardening exponent and the strain at the load maximum both before and after charging, grain boundary fracture is estimated to be introduced after load maximum point, viz. under the condition of dσ/dε<σ.

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Shirasu/Aluminum functionally gradient materials (FGMs) were successfully fabricated by centrifugal casting method, where Shirasu is volcanic eruptions accumulated over the south kyushu in Japan. Thermal conductivity of Shirasu/Aluminum FGM was measured by a comparative method in two directions, i. e. perpendicular and parallel to the gradient direction. The thermal conductivity was theoretically estimated using the equation derived by Bruggeman both on Shirasu/Aluminum FGMs and uniformly dispersed Shirasu/Aluminum composites. It has been found that the thermal conductivity of the Shirasu/Aluminum FGMs in the perpendicular direction to the gradient is larger than that in the parallel direction. The anisotropy in the thermal conductivity obtained by the experiment is found to be larger than that predicted by the calculation. Since the Shirasu/Aluminum FGM has a strong anisotoropy in the thermal conductivity, this FGM can be used as a good heat-insulating material, compared with the uniform composite which contains the same amount of Shirasu.

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Rapidly solidified flakes of Al-8 mass%Y based alloys with or without additions of 4 mass%Fe, Mn, Cr and Ni were produced by atomizing and subsequent splat quenching on a water-cooled copper roll. Consolidation of the flakes was done by cold pressing, vacuum degassing and hot extrusion at a reduction ratio of 25 to 1.Extended solid solubility of Y was obtained in as rapidly solidified state. The microstructures of as-extruded P/M materials consist of matrix of fine sub-grains with dispersion of fine intermetallic compounds. The size of compounds in the Cr-bearing alloy was finer than in the other alloys. P/M materials contained transition metals show tensile strength higher than 420MPa combined with elongation higher than 12%at room temperature. Among them, Cr-bearing alloy shows the highest tensile strength of 524MPa at room temperature, 370MPa at 473K and 218MPa at 573K.

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Al-Zn-Si alloy bearings are widely used for diesel engines. But recently some cases of fatigue damages and cavitation errosion have been reported in application for new high output engines. Al-Zn-Si alloys were investigated from a metallurgical point of view to prevent such phenomena. It is comfirmed that both addition of magnesium and increase in content of silicon to the alloys are effective for improvement of mechanical properties, especially hardness and tensile strength. A high solidification rate casting makes silicon particle size finer and more uniformly distributed than the conventional casting. Finer and more uniformly dispersed silicon particles improve not only static strength but also fatigue strength and cavitation resistance. The bearings made of the new alloy cast at a high cooling rate show better performance on bearing test machines.

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A forming roll was introduced in a conventional melt spinning process to improve free solidified surface of the strip. Effect of the forming roll was tested at the condition as below. Roll speed ranges from 2 to 12m/s. Roll gap is 0.2mm. Slit size is 0.8 × 20mm. Ejection gas pressure is 20kPa. Distance between nozzle and forming roll ranges from 40 to 160mm. Forming load is 98N. Specimen is Al-12 mass%Si alloy. Roll speed and nozzle-forming roll distance are the most important factors in this process. Because they affect the solidification on the free solidified surface. The flatness and microstructure of the strip can be made sound by the modified process of this study.

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Vacuum brazability of aluminum was investigated using various Al-Si-Mg powder brazing filler metals made by atomization. The effects of atomizing atmosphere and powder size on brazability were studied. After brazing a part of used filler metals gave no contribution for the fillet formation and gathered on the base metal, showing non-wetting among filler metal powders. Brazability was evaluated by the percentage of the filler metal remaining as fillet by measuring the weight change before and after brazing. After brazing of the powder filler metal, voids were found in the formed fillet. Although the completely sound fillet was not obtained, the fine powders and air atomized powders gave better brazability than coarse powders and those atomized in argon gas atmosphere. The difference in vaporization characteristics of magnesium in the filler metals seemed to be responsible for the void formation and poor brazability of the powder filler metals. Mixing of the filler metals with the Al-Mg powder was found to be effective for the improvement of the fillet formation, however, completely sound fillet was not obtained. It is believed that both the control of magnesium vaporization rate and the improvement of quality of vacuum are important to obtain the sound fillet using powder filler metals.

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Tool wear and cutting resistance were larger for the alloy strengthened by harder ceramic particles, and took maximum for alloys containing Al₂O₃ or SiC. Further, they increased simultaniously during machining, and were related uniquely to the cutting distance irrespective of the cutting speed. The tool wear proceeds mainly by mechanical abrasion due to ceramic particles in the alloys. The principal cutting force originates from the friction force due to tool wear. However, the wear of a sintered diamond tool was small even for alloys containing Al₂O₃ or SiC, suggesting that tool wear and cutting resistance also are reduced in case that the hardness of particles in a tool exceeds that in a work material.

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