J. Mater. Sci. Technol. ›› 2021, Vol. 71: 152-162.DOI: 10.1016/j.jmst.2020.07.032

• Research Article • Previous Articles     Next Articles

Twin crystal structured Al-10 wt.% Mg alloy over broad velocity conditions achieved by high thermal gradient directional solidification

Luyan Yanga,b,c, Shuangming Lib,*(), Kai Fanb, Yang Lib, Yanhui Chena,*(), Wei Lia, Deli Konga,c, Pengfei Caoc, Haibo Longa, Ang Lia   

  1. a Institute of Microstructure and Properties of Advanced Materials, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing, 100124, China
    b State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an, 710072, China
    c Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, 52428, Jülich, Germany
  • Received:2020-05-29 Revised:2020-07-15 Accepted:2020-07-27 Published:2021-04-30 Online:2021-04-30
  • Contact: Shuangming Li,Yanhui Chen
  • About author:yhchen@bjut.edu.cn (Y. Chen).
    * E-mail addresses: lsm@nwpu.edu.cn (S. Li),

Abstract:

Twin crystal structured Al-10 wt.% Mg alloys that were grown over a broad solidification velocity range were prepared and studied for the first time. The high thermal gradient (G) and growth velocity (V) of directional solidification resulted in the dominant solidification of twins: the twinned dendrite trunks at constant high Vs curved in the G direction with large angles in 7 mm diameter crucibles and invaded regular columnar grains because of a distinct kinetics growth advantage. Transitive deceleration experiments were designed to produce twin crystals that evolved with lower values of V (100, 10, and 0.5 μm/s) and had a structural coarsening trend. Twin cell growth in the absence of arms occurred at a growth velocity of 10 μm/s. A coherency loss was observed at a growth velocity of 0.5 μm/s with straight coherent twin boundaries turning into curved incoherent boundaries. Linear theoretical analyses were performed to understand the structural evolution of the twins. These results demonstrate the possibility of producing dense and controlled twin crystals in the Al-Mg system under most industrial production conditions; thus, this approach can be a new structural choice for designing Al-Mg-based alloys that have widespread commercial applications.

Key words: Directional solidification, Aluminum alloy, Microstructural evolution, Feathery crystals, Twinned dendrites