Corrosion Resistance of AZ91D Magnesium Alloy under Different Treatment Processes
The microstructure of solid solution,as-extruded AZ91D and aged-extruded AZ91D magnesium alloy was analyzed by optical microscopy,electron microscopy and XRD.AZ91D magnesium alloy in the as-cast,solid solution,and extruded states was analyzed through potential polarization,salt spray corrosion,and immersion corrosion weight loss experiments.The results indicate that the corrosion resistance of extruded AZ91D magnesium alloy is superior to that of solid solution ones,and that of extruded AZ91D magnesium alloy after aging treatment is better than that of extruded ones.After solid solution treatment,β-Mg17Al12 phase is continuously dissolved into α matrix to form the supersaturated solid solution,and a large amount of β phases are precipitated from supersaturated solid solution α phase in the solid solution AZ91D magnesium alloy during the hot extrusion process,which are distributed along grain bound-aries.Corrosion resistance of as-extruded AZ91D is improved as a result of Al increasing the corrosion potential of magnesium alloys,reducing corrosion tendency to delay the corrosion rate.The aging process can eliminate residual stresses that occurs in the material during hot extrusion,resulting in the more uniform distribution of β-Mg17Al12 phase along grain boundaries,further improving the corrosion resistance of AZ91D magnesium alloy.
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