Effect of rare earth and silicon additions on structure and properties of melt spun Mg–9Al–1Zn alloy

Abstract

Abstract Magnesium based Mg–9Al–1Zn–5RE (RE=Y, La, Nd, Ce, or Pr) alloys with or without an addition of 1%Si were rapidly solidified by chill block melt spinning and splat quenching. The base alloy AZ91 (Mg–9Al–1Zn) was also rapidly solidified. Isochronal heat treatment for 1 h at 100–400°C showed that the microhardness of the ribbon maintained a similar level to that of the as spun alloy up to 300°C but decreased when heat treated at 400°C. Isothermal heat treatment for up to 24 h at 250–350°C showed that there were aging responses for the sample treated at 250°C while above this temperature, the microhardness decreased as the treatment time increased. The addition of 5% of RE elements to AZ91 displaced the Mg17Al12 phase in AZ91 with fine dispersoids of Al2RE (RE=Y or Nd) or Al11RE3 (RE=La, Nd, Ce, or Pr) in Mg–9Al–1Zn–5RE alloys. These Al–RE intermetallics remained fine and precipitated at the grain boundaries so restraining grain growth during heat treatment at up to 400°C. Although Mg2Si precipitates...