Study of the isochronal annealing of high pressure die-cast magnesium alloy AZ91 by positron annihilation lifetime technique

Abstract EN

The structure variations for AZ91 (Magnesium- 9%Al- 1%Zn) during isochronal Annealing from RT to 450oC was studied using positron annihilation lifetime (PAL), microhardness measurements, scanning electron microscope (SEM) and X ray diffraction (XRD) techniques.

The results of lifetime and microhardness reveals four stages of annealing, from RT to 100 oC represents the recovery process with formation of small amounts of intermetallic precipitates like Mg17Al12 and Al-Mn.

From (100 to 180 oC) is a competition between precipitation and a release of more defects.

The third stage (180 to 300 oC) may refer to complete relief of the remained defects with some precipitations.

The fourth one (300 to 450 oC) is rearrangement of grains and grain growth.

The positrons trapping rate (k) and the volume fraction (α) of the trapping positrons in 3D defects are calculated from lifetime parameters.