Codeposition of Al and Si onto a low carbon steel using silicon dioxide and aluminum and its hot temperature oxidation properties

Al and Si were simultaneously deposited onto a low carbon steel by pack cementation process using elemental Al and SiO2 powders as Al and Si sources. A series of silicon-containing aluminide coatings have been produced by varying the content of SiO2 (with the fixed Al content) in the pack at an elevated temperature. When processed in a pack using a dual activator of NaCl+KBF4 at 1000 °C, the content of Al reached approximately 45 wt.% at the surface of pure aluminide coatings, but decreased monotonically with an increase in the content of SiO2 in the pack. The maximum content of Si at the surface was measured to be approximately 4.5 wt.% for the pack composition of 8.3Al–7.5SiO2 in wt.%. The decrease in the Al content was attributed to the activated conversion of SiO2 to Si by elemental Al during the process. These aluminized low carbon steels were undergone cyclic oxidation tests at 900 °C in air, and showed good oxidation-resistant properties within approximately 30 h of testing period when the aluminide coatings were modified by Si approximately 3 wt.% at the surface.