Surface layers enriched with Al and Si were fabricated on an AZ91D substrate using thermochemical treatment in solid media. The AZ91D specimens were heated in an Al+Si powder mixture acting as a source of diffusion elements. Two temperatures were applied: 430 oC and 445 oC. The microstructural characterization of the layers was performed using an optical microscope and a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (EDS). The layer produced at 430 oC had a thickness of 50 µm; the structure was composed of intermetallic Mg17Al12 and Al3Mg2 phases and an Mg2Si phase. When a higher temperature (445 oC) was used, the layer was much thicker (600 µm) and the structure was predominantly a eutectic (an Mg17Al12 intermetallic phase + a solid solution of Al in Mg) with agglomerates of Mg2Si phase particles distributed over the eutectic matrix.Keywords: Magnesium alloy, thermochemical treatment, diffusion, surface layer, microstructure
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