The Research On Anodizing Of Magnesium Alloys Under Restraining Sparking

This paper investigated the surface reinforcement of magnesium and its alloys systematically using anodizing technology under restraining sparking in mixed alkaline solutions composed of ammonium phosphate, sodium fluoride, organic amine and film-forming additive. The properties ingredients appearances and structures of the oxide films were examined by HVS-1000 sclerometerv CTG-10 vortex flow thickmeter, EDS and SEM etc. On this condition, the organic amine, as additive of restraining sparking, was studied about its effect on anodizing of magnesium alloys. Moreover, the capacities of restraining sparking of different kinds of organic amine were discussed. Additionally, the equipments and process of anodizing technology under restraining sparking using to MB2 magnesium alloys warhead were also tentatively studied in this paper.Technical research shows that electrolysis parameters, such as electrolyte ingredients, concentration, value of pH and peak current density have distinct effect on properties of oxide film. Other ingredients, for example, reaction time, agitation intensity and temperature et al. only have common effect. In mixed alkaline solution, smooth lustrous analogous ceramic films could be deposited on AZ91D magnesium alloys using anodizing technology under following conditions, organic amine A 40~ 100 g/L, ammonium phosphate monobasic 2~10 g/L, sodium fluoride 1~5 g/L, film-forming additive 0.25~2.0 g/L, peak current density 12.0~28.0 A/dm2, value of pH 9~12, weak agitation, temperature 25~40 癈. The analogous ceramic film shows a thickness of 15~40u,m, a micro-hardness of 200~420HV. According to the cross experiment design, the best film-formation condition is that: organic amine A 100 g/L, ammonium phosphate monobasic 8 g/L, sodium fluoride 3 g/L, film-forming additive 1.0 g/L, value of pH 11 ~ 12.Organic amine which is additive of restraining sparking in the anodizing process has apparent ability of restraining sparking to the high voltage anodization of magnesium alloys which advances with the concentration of organic amine increasing. Apparent difference is exhibited between the various kinds of organic amine. With the concentration of organic amine increased, the films had deeper color, lower thickness and higher hardness. The film revealed numerous pores which is channels through which the gas sent out when anodizing. Furthermore, many traces analogous tosintered ceramic materials were observed on the surface which may result in superiorproperties such as hardness and corrosion protection. The effect of organic amine on anodizing of magnesium alloys is facilitating the formed film intact and compact, which results high breakdown voltage, hardness and good corrosion resistance.The EDS results show that the main content elements of oxide film of AZ91D magnesium alloys are Mg, P, Al and O, simultaneity, the minor elements F, C, Mn and Ni. The content of Mg in the anodic film increases from the surface of the film to the AZ91D substrate. The content of P enhances rapidly with the distance embedding near the surface of the film, and keeps stabile in the middle part of the film, however, descends promptly in the interface of film/substrate which distribution shows undee on the whole. Al in the film originates from the substrate and is retained in the film by oxidation during film formation. F element may originate from the electrolyte by mingling or absorption. Analysis to SEM micrograph of the AZ91D magnesium surface and cross-section of anodic film shows that the surface of AZ91D was covered with a smooth and uniform film. Numerous pores were clearly seen. The film revealed pores of typical diameter in the range 1-3 urn which is similar to that of the conventional anodic ones. Many traces analogous to sintered ceramic materials were observed on the surface. This may result in superior properties such as hardness and corrosion protection. The film consists of a double-layer structure: the outer loose layer and the inner compact layer. There are many groove micro-cracks in the compact layer...