Correlations Between the Atmosphere Conditions on the Natural Aluminum Oxide Layer and the Brazeability

Due to its good material properties, the consumption of aluminum alloys is continuously increasing. One important advantage of aluminum is its very good corrosion resistance. This property is based on the natural oxide layer (Al₂O₃). The thickness and composition of the natural layer is strong influenced by the atmospheric conditions, e. g. the temperature and humidity, but also by the composition of the base material.

A lot of technical applications require a joining by material bonding, e. g. brazing. For this type of joints, the natural oxide layer at the surface of aluminum materials has to be destroyed. Unfortunately, there are no investigations about the correlation between the oxide layer thickness and composition and the brazeability until now available in the literature.

In the presentation, methods for analyzing the nm thick layers will be described (mainly XPS and FTIR). These methods are used to show the influence of humidity on the natural oxide layer, e. g. during transport and storage of the materials. Furthermore, the influence of rising temperatures on the diffusion inside the materials as well as on the oxidation behavior of the surface will be presented. Additionally, brazing tests will be introduced. These tests were done in a shielding gas furnace without using flux with aluminum materials with thicker oxide layers due to storage in a higher humidity. The mechanisms of surface activation will be also described. Due to these tests, the understanding about the correlation between the storage conditions, the natural oxide layer and the brazeability of the material will be enhanced.