Abstract
The powder thermal diffusion alloying method could be utilized to fabricate Al-rich intermetallic coatings on magnesium alloys in the air. While the role of ammonium chloride powder in the diffusion alloying source is still to be investigated. This research took the AZ91D magnesium alloy as the substrate. Diffusion sources with various powders were utilized as the diffusion source. Microstructure observation and phase identification were enrolled to investigate the role of the ammonium chloride powder in the diffusion alloying process. Results indicate that HCl gas could turn some solid Al powder into gaseous AlCl3 to enhance the transport of active Al atoms, moreover, it reacts with the dense MgO film and converts it to a loose one, which enables the AlCl3 gas to penetrate MgO and arrive the matrix to form a protective coating. Furthermore, the ammonium chloride content should be confined to 10 wt. % of the diffusion alloying source. Too much ammonium chloride powder would result in a worse intermetallic coating.
Highlights
Magnesium alloys are easy to be corroded and this limits their utilization [1,2,3,4]
To utilize NH4 Cl powder effectively, powder thermal diffusion alloying processes with various NH4 Cl contents in the diffusion source were carried out to fabricate Al-rich intermetallic coatings on the AZ91D magnesium alloy specimens
HCl gas could react with Al powder and produce AlCl3 gas
Summary
Magnesium alloys are easy to be corroded and this limits their utilization [1,2,3,4]. By the diffusion alloying method, metallic atoms could be added to the matrix of magnesium alloys continuously for the corrosion resistant coatings to form [8,9,10,11,12,13,14]. The as-diffusion alloyed Al-rich intermetallic coating usually composed of two phases, a light phase and a dark phase [3,4,14,15,16]. The increased ammonium chloride content would promote the formation of the intermetallic coating further. To utilize NH4 Cl powder effectively, powder thermal diffusion alloying processes with various NH4 Cl contents in the diffusion source were carried out to fabricate Al-rich intermetallic coatings on the AZ91D magnesium alloy specimens. It is hoped that the corresponding results would be helpful for utilizing NH4 Cl powder more rationally to fabricate better intermetallic coatings, to save materials and to alleviate air pollution and device degradation
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