Photo 4 Step-aged structures in specimens of 0.1mm thickness (pre-aging time, 15min). Rerfer to Fig. 7. Foil orientation, [001]. The figure shows that the structure is not homogeneous in this case.

No abstract

No abstract

The ductility of Al-5wt%Mg alloy at elevated temperatures which was affected by a trace addition of Y, Ce, Sm and Be or by melting atmospheres was examined. Tensile tests in vacuum were made in a temperature range from in accord with the previous papers. However, the embrittlement almost disappeared by the addition of Y, Ce, Sm and Be when the alloy was prepared by melting in air. The phenomenon was attributed to the fact that formation and growth of cavities on grain boundaries were effectively checked, because strain-induced boundary migration easily occurred during tensile tests in those alloys. It was suggested that the high-temperature embrittlement so far reported was related to certain gas impurity atoms introduced in the course of melting in air. The impurity atoms would prevent the boundary migration. The additives would have a strong interaction with the impurity atoms above described.

Effect of heat treatment conditions such as atmosphere, temperature and time on the hydrogen content in two Al-4%Mg alloys was investigated. The hydrogen content in the as-cast slab is dispersed uniformly, while the hydrogen content in the annealed slab tends to be increased in the area near the surface. Such a condensation of hydrogen near the surface can be seen when it is annealed in a wet atmosphere. When annealed in a dry atmosphere, the hydrogen content near the surface becomes lower than that of the center of the specimen. Although the hydrogen in Al-Mg alloy tends to be released to outside at temperatures higher than 400°C, the absorption of hydrogen existing in the atmosphere is also presumed to occur at the same time when annealed in the wet atmosphere.