Materials Processing for Structural Stability in a ZK60 Magnesium Alloy

Abstract

The materials processing, consisted of a four step process of solution treatment, pre-strain, overaging and hot working, was developed for attaining structural stability at high temperatures in a commercial Mg-Zn-Zr alloy, ZK60. The grain size of the material processed by this schedule was refined to 2.5 mm, and the material behaved in a superplastic manner at 548 K and at a strain rate of 1 Â 10 À2 s À1 owing to the grain size stability at this temperature. From the analysis of the chemical composition of precipitates, it was suggested that the phase Mg 7 (Zn,Zr) 3 , which was not observed in material without pre-strain, was effective in pinning the grain boundaries at high temperatures.

Dislocation Configurations in an Extruded ZK60 Magnesium Alloy

“…These precipitates are MgM (M = Zn,Zr) intermetallics, according to energy dispersive X-ray spectroscopy characterization by Watanabe et al [25] Figure 5 shows the dissociation of a dislocation. The split width is narrow, suggesting a relatively high stacking fault energy (SFE).…”

Role of Zr in the Microstructure Evolution in Mg‐Zn‐Zr Based Wrought Alloys

“…The rods growing along the [0001] direction are the Pi' phase, and the Pi' phase have the size of 620 ±150 nm in length and 30 ± 10 nm in diameter. The plates are the P2' phase [6], and they have the size of 30 ± 10 nm in thickness and 10 ± 5 nm in diameter. Figure 3 The fii' and P2' phases observed in the as-cast sample are much coarser than those observed in the heat treated sample [8], However, EDS elemental maps clearly confirms the presence of the Mg(Zn,Zr) phase.…”

“…Zr-enriched cores formed during melting have been believed to provide nucleation sites for the magnesium grains leading to the grain refinement [2][3][4][5], Recent studies have reported some overlooked roles of Zr in the Mg-Zn based alloys [6][7][8][9][10], Bhattacharjee et al reported that Mg(Zn,Zr) precipitates are formed in a ZK60 cast alloy subjected to a heat treatment at 350°C [8], The structure of the Mg(Zn,Zr) precipitates were identical to MgZm type phases of Pi' and P2' phases, which are typically observed in the Mg-6Zn (Z6) alloy subjected to aging. Since the J31' and P2' phases in the aged Mg-6Zn (Z6) alloy are dissolved by heat treatment at 350 °C, they concluded that Zr stabilized the Pi' and P2' precipitates at elevated temperature.…”

Synergetic Effect of Grain Refinement and Spherical Shaped Precipitate Dispersions in Fracture Toughness of a Mg-Zn-Zr Alloy

“…Rod shaped precipitates were formed, and the similar shaped precipitates have been observed by aging process. [21][22][23] Similar aging conditions occurred in the extrusion container before extrusion. Therefore, it is assumed that the spherical shaped precipitates were formed during the extrusion process in comparison with Fig.…”