Study on the blistering of aluminium (1st Report)

Abstract

The authors studied the effect of the dew point in the heating atmosphere and the effect of very small amounts of iron, silicon and beryllium added in super-purity aluminium on the blisters originating from the reaction of water vapour and aluminium. Further, the difference of electron diffraction patterns in two kinds of oxide film having the different effect on preventing the blisters and also the blistering rate at various heating temperature were studied.The results are as follows:(1) It is necessary to keep the dew point under about 5°C in air and about 10°C in nitrogen atmosphere in order to anneal 99.99% aluminium without blistering at 500°C.(2) Very small additions of iron and silicon to super-purity aluminium cause to increase the blisters. Although iron does not affect the blistering at the lower temperature such as 300°C, silicon causes slightly to increase the blistering.(3) Addition over 0.003% beryllium is proved to prevent the blistering completely.(4) The oxide film formed at higher temperature than 450-500°C in dry air distinctly affects to prevent the blistering. This oxide film showed the dotted diffraction ring whereas the oxide film formed at lower temperature (440°C) showing the perfect ring pattern has not the protective effect of blistering. In other words, the oxide film having a grown crystalline oxide by raising temperature, acts to prevent the blistering as compared with that having very small crystalline oxide formed at lower temperature.(5) There is a linear relation between the logarithm of blistering speed and the inverse of annealing absolute temperature.