Fabrication and microstructural characterization of Al/Zn-enriched layers on pure magnesium

Al/Zn-enriched surface layers were fabricated by heating Mg specimens in contact with Al–Zn powder mixtures in a vacuum furnace at 445 °C. The layer formation process took place through partial melting at the Mg-substrate/powder-mixture interface. Heating times ranged from 20 to 80 min. The layer microstructure and composition were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The layers were 100–900 μm in thickness, depending on the treatment time. The examination results revealed that the layers consisted of Mg17(Al,Zn)12 and Mg5Al2Zn2 intermetallic phases and a solid solution of Al and Zn in Mg. Between the Al/Zn-enriched layer and the Mg substrate, there was a transition zone of a solid solution of Al and Zn in Mg with a thickness of 20–30 μm. The layers had much higher microhardness than the Mg substrate.

► The layers were produced by heating Mg in contact with an Al–Zn powder mixture.
► The layer formation process at 445 °C proceeded with the liquid phase contribution.
► The Al/Zn-enriched layers were thick, dense, uniform and continuous.
► The layers contained Mg–Al–Zn intermetallic phases.
► The hardness of the layers was much higher than that of the Mg substrate.