Surface Corrosion of Mg-Containing Al-Based Alloys

Abstract

During heat‐treatment of Mg‐containing Al‐based alloys, the Mg concentration changes considerably. As compared to the pure material significant surface corrosion is observed for the air heattreated alloy. In vacuum heat treatment the Mg content of the surface layer increases considerably. Initially metallic Mg is detected on the surface which, however, becomes oxidized later on. On the basis of the investigations one has to assume that the process is not a simple diffusion mechanism only. A new conception is formed for the process according to which it is controlled by the breaking up of the Al2O3 barrier layer by Mg.

On the L2, 3 Soft X-Ray Emission of Al in AI-Mg Alloys

“…9), and the measured one for AlMg alloys (about 64 eV) ( Fig. 5) show the overcoated oxidation enrichment effect which is described elsewhere [6]. The control measurements on the Mg L2, emission spectra clearly show the oxidation, but from the A1 L2, emission alone the deconvolution of the real Mg enrichment and oxidation effects is not possible because the heavy overlapping of these peaks.…”

“…10, where the peak characterizing the oxides appears at lower excitation. According to our study we can be sure that the explanations of the effects measured before [6] are essentially correct, only a refinement is needed taking into account the absorption effects as well. The magnesium side has also been examined, and all the previous conclusions have been found correct in the light of these new facts, too.…”

“…Especially the soft X-ray emission of the A1-Mg alloys has been widely measured by the A1 Lz,3 [5] and also by the Mg L2,3 specra [6]. The spectra refer to the partial density of s + d electronic states (s + d PDOS) [3] and are sensitive enough to the chemical bonds of aluminium [7].…”

“…The Fermi edge itself is sensitive to band effects [7,81 and to the stability of alloys [9 to 111. The spectra give good information on surface effects [6], because the penetration of the exciting electrons and the attenuation length of the outgoing photons are small, giving proper information from the near vicinity of the surface [12,131. O n the other hand, the obtained soft X-ray signal characterizes a layer which is deep enough to neglect the direct, hardly controllable surface effects, as for example the roughness, pollutions, adsorbates, etc.…”