Formation of precipitates in parallel arrays on LPSO structures during hot deformation of GZ41K magnesium alloy

Abstract

(Mg,Zn)3Gd precipitates were observed in the form of parallel arrays within a α-Mg matrix of a Mg-3.5Gd-1Zn-0.6Zr (GZ41K) alloy following isothermal holding at 450 ℃ for 20 min or uniaxial hot compression testing at 450 ℃ and at strain rates of 10-3 s-1 and 10-1 s-1. A microstructural analysis using a combination of scanning and transmission electron microscopies showed arrays of precipitates nucleated on stacking faults as a result of the LPSO structures decomposing statically after long isothermal holding times at 450 ℃, which is lower than the dissolution temperature of (Mg,Zn)3Gd precipitates (520 ℃), and dynamically, as a result of hot compression. The presence of precipitates on slip bands was also observed in the case of deformed specimens. The characteristics of the precipitates were investigated using differential thermal analysis, and optical and electron microscopy. The influences of the solutionizing temperature and deformation conditions on distribution, morphology and volume fraction of precipitates were quantified. The results are interpreted in terms of the influence of the strain rate in increasing the stacking fault/dislocation intersections and the decomposition of the L1 2 structure of stacking faults.

Twin-assisted precipitation during hot compression of an Mg-Gd-Zn-Zr magnesium alloy

“…5d reveals that dynamic precipitation has occurred before twinning. Otherwise, as has been observed for the static precipitation of a similar alloy in a twinned matrix [28], the precipitate line should be broken at twin boundaries.…”

“…In the present study, deformation by slip of dislocations before nucleation of twins at the initial stages of hot compression at 350℃ resulted in the dynamic precipitation in parallel rows on stacking faults. In a previous study [28], the authors also observed dynamic precipitation on some deformation slip planes. The above findings can be related to the effect of compressive load on the decomposition of solute-enriched stacking faults to the (Mg,Zn)3Gd precipitates.…”

“…This precipitation behavior originated from deformation by slip of dislocations in non-twinned grains. In a previous study [28], the authors showed that while two LPSO and (Mg,Zn)3Gd phases coexist in the Mg matrix, dissolving the (Mg,Zn)3Gd phase during solutionizing leads to an excess formation of the LPSO structure. Also, it was shown that below the dissolution temperature of the (Mg,Zn)3Gd phase, applying compressive loads could result in the decomposition of the LPSO structure and the precipitation of the (Mg,Zn)3Gd phase.…”

“…5d) revealed that these parallel arrays of precipitates crossed the twins without any change in their alignment. This indicates that these parallel rows of precipitates formed before the development of twins, and result from the effect of the compressive load on precipitation from solute-enriched stacking faults[28].It is worth noting that the morphologies of the precipitates present in the twinned and non-twinned grains are very different. A comparison of the dynamic precipitation in the twinned and nontwinned grains (Fig.…”

Hot Deformation Behavior and Hardness of a CoCrFeMnNi High-Entropy Alloy with High Content of Carbon

“…Also, a processing map is an effective method to determine the optimum working conditions. In the meantime, hot deformation can promote the formation of the precipitated phases, and a possible governing mechanism can be obtained [30]. Therefore, the heavy carbon addition into CoCrFeMnNi HEA may result in both high hardness and relatively suitable hot workability and thus is valuable to explore.…”