Synchrotron tomographic quantification of the influence of Zn concentration on dendritic growth in Mg-Zn alloys

Abstract

Dendritic microstructural evolution during the solidification of Mg-Zn alloys was investigated as a function of Zn concentration using in situ synchrotron X-ray tomography. We reveal that increasing Zn content from 25 wt.% to 50 wt.% causes a Dendrite Orientation Transition (DOT) from a six-fold snowflake structure to a hyper-branched morphology and then back to a six-fold structure. This transition was attributed to changes in the anisotropy of the solid-liquid interfacial energy caused by the increase in Zn concentration. Further, doublon, triplon and quadruplon tip splitting mechanisms were shown to be active in the Mg-38wt.%Zn alloy, creating a hyper-branched structure. Using the synchrotron tomography datasets, we quantify, for the first time, the evolution of grain structures during the solidification of these alloys, including dendrite tip velocity in the mushy zone, solid fraction, and specific surface area. The results are also compared to existing models. The results demonstrate the complexity in dendritic pattern formation in hcp systems, providing critical input data for the microstructural models used for integrated computational materials engineering of Mg alloys.

Effect of Zn Content on the Microstructure and Mechanical Properties of Mg–Al–Sn–Mn Alloys

“…For Mg–6Al–3Sn–0.25Mn– x Zn alloys, the volume fraction of the phases is 9.6%, 11.9%, 17.7%, 22.6%, and 24.5%, respectively. It can be considered that the formed second phase effectively reduces dendrite spacing and promotes cast grain refinement [17].…”

Study on Porous Mg-Zn-Zr ZK61 Alloys Produced by Laser Additive Manufacturing

“…They reveal that increasing Zn content from 25 wt.% to 50 wt.% causes a Dendrite Orientation Transition (DOT) from a six-fold snow-flake structure to a hyper-branched morphology and then back to a six-fold structure. This transition was attributed to changes in the anisotropy of the solid-liquid interfacial energy caused by the increase in Zn concentration [36,37]. Further, doublon, triplon and quadruplon tip splitting mechanisms were shown to be active in the Mg-38 wt.% Zn alloy, creating a hyper-branched structure.…”

“…Therefore, this proves that as the Zn content increases, the grain size has been significantly refined. Recent papers [36,37] demonstrated that dendritic microstructural evolution during the solidification of Mg-Zn alloys was investigated as a function of Zn concentration using in situ synchrotron X-ray tomography (Shanghai Synchrotron Radiation Facility, Shanghai, China). They reveal that increasing Zn content from 25 wt.% to 50 wt.% causes a Dendrite Orientation Transition (DOT) from a six-fold snow-flake structure to a hyper-branched morphology and then back to a six-fold structure.…”

Microstructure, Tensile Properties and Work Hardening Behavior of an Extruded Mg–Zn–Ca–Mn Magnesium Alloy

“…There has been much attention given to magnesium alloys containing high concentrations of Zn (usually between 3 and 6 wt%) [10][11][12] and low concentrations of Ca (usually between 0.2 and 1 wt%) [13][14][15][16][17][18]. Du et al [10] found that the tensile strength of an as-extruded Mg-6 wt% Zn alloy could be effectively improved by Ca (0.36-0.82 wt%) addition.…”

“…Xu et al [11] reported that during indirect extrusion process, fine-grained structures were preferentially formed in the untwinned matrix and near the intermetallic compounds in Mg-5.99Zn-1.76Ca-0.35Mn (wt%) alloy. Shuai et al [12] investigated the anisotropy of the solid-liquid interfacial energy for Mg-Zn alloys, which increased with increasing the Zn concentration to 50 wt%. Oh-ishi et al [13] obtained the highest peak hardness of a Mg-0.3Ca-Zn alloy as Zn additions up to 0.6 (at%).…”