This paper was studied on the high temperature corrosion characteristics of Al-Si-Mg alloys in Air, O2 and H2S/H2 environments. The composition aluminum alloys were (1) A1 ? Al7Si0.4Mg alloy and (2) A2 ? Al1Si1Mg alloy. From these results the following conclusions can be drawn.
The weight gain and the reaction rate constants of the A1 alloy were measured in the air, oxidation and sulfidation environments at 773K. The weight gain showed parabolic behavior in air and oxygen environments. The weight gain in the hydrogen sulfide environment was showed linearly behavior. The reaction rate constants were confirmed to be kp=1.26× 10-4mg2cm-4sec-1 in air and kp=1.95×10-4mg2cm-4sec-1 in an oxygen environment and kl=6.22×10-4mg2cm-4sec-1 in the hydrogen sulfide environment. The reaction rate was about 3.2 times increased in the hydrogen sulfide environment than the oxygen environment.
The weight gain and the reaction rate constants of the A2 alloy were measured in air, oxidation and sulfidation environments at 773K. The weight gain showed parabolic behavior in the air and oxygen environments and were increased linearly in the hydrogen sulfide environment. The reaction rate constants were confirmed to be kp=1.676×10-4mg2cm-4sec-1 in an air and kp=1.981×10-4mg2cm-4sec-1 in an oxygen environment and kl=6.19×10-4mg2 cm-4sec-1 in the hydrogen sulfide environment respectively. The reaction rate was about 3.1 times increased in the hydrogen sulfide environment than in oxygen environment.
After dry corrosion test, the corroded surface was observed using XPS. The Al2O3 and MgO compounds were detected in the surface of Al-Si-Mg alloys tested the oxygen environment and Al2O3 and Al2(SO4)3 compounds were in the hydrogen sulfide environment.
When the Al-Si-Mg alloys, A1 and A2 were tested in the dry environment of air, oxygen and hydrogen sulfide gas environments at 773K, they showed a good corrosion resistance in an air and oxygen environment but their resistance was rapidly decreased in a hydrogen sulfide environment. The Al2O3 oxide film was formed on the surface in the oxygen environment. This oxide film prevented further oxygen environment. The unstabled Al2O3 oxide film was also formed on the surface in the hydrogen sulfide environment. External migration of Al element through the Al2O3 oxide film and sulfur ion was internaly migration to alloy substrate and Al2(SO4)3 product reaction was continued.