Surface alloying of AZ91E alloy by Al-Zn packed powder diffusion coating

► A new packed powder diffusion coating (PPDC) technique for Mg alloys is reported. ► The role of Zn as a catalyst activating the diffusion of Al into Mg is discussed. ► PPDC produces thick, dense and uniform Al-Mg-Zn intermetallic coating at temperatures below 420 °C. ► The formation mechanism of such coating on Mg substrate is proposed and discussed. ► Compare to Mg alloy substrate, the coating shows high corrosion resistance and high hardness.