Revealing the Diversity of Dendritic Morphology Evolution During Solidification of Magnesium Alloys using Synchrotron X-ray Imaging:A Review

摘要

In this paper,the diversity of complicated dendrite microstructure and its evolution behavior during solidification in different magnesium alloys under various processing conditions were illustrated using synchrotron X-ray imaging technique.A variety of dendritic morphologies and branching structures were revealed,i.e.,sixfold plate-like symmetric structure in Mg-Al-based structure,12-branch structure in Mg-Zn-based alloys and 18-branch structure in Mg-Sn-and Mg-Ca-based alloys as well as seaweed like hyper-branched structure in Mg-38wt%Zn alloy.In addition,a dendrite morphology and orientation transition with increasing addition of Zn content were also observed in Mg-Zn alloy,with dendrite growth pattern transform from anisotropy(low Zn addition)with sixfold symmetric snow-flake structure to relative isotropy(intermediate Zn addition)where seaweed morphology presented and then back to anisotropy(high Zn addition)when only 12 branches with preferredorientations were observed.The phase-field model representing the typical dendritic morphologies and branching structures under various conditions was also depicted and discussed.Further,the two-dimensional(2D)real-time dendrite growth dynamics in different Mg-based alloys captured using synchrotron X-ray radiography for unveiling the originate of theα-Mg dendrite was reviewed.Following this,the four-dimensional(3D+time)synchrotron X-ray tomographic in situ observation of dendritic morphology evolution indicating the formation mechanism of the diverse dendritic morphology during Mg-Sn-and Mg-Zn-based alloys was also summarized.Finally,the future study on exploring the complicated dendritic morphologies and their origination during solidification of Mg-based alloys is prospected.