J. Mater. Sci. Technol. ›› 2024, Vol. 184: 167-179.DOI: 10.1016/j.jmst.2023.10.027

• Research article • Previous Articles     Next Articles

Balanced strength and ductility by asymmetric gradient nanostructure in AZ91 Mg alloy

Bingqian Xua, Jiapeng Suna,*, Lingling Wanga, Jing Hanb, Guosong Wua,*   

  1. aCollege of Mechanics and Materials, Hohai University, Nanjing 211100, China;
    bSchool of Mechanical and Electrical Engineering, China University of Mining and Technology, Xuzhou 221116, China
  • Received:2023-06-08 Revised:2023-09-19 Accepted:2023-10-02 Published:2024-06-10 Online:2023-11-28
  • Contact: *E-mail addresses: sun.jiap@gmail.com (J. Sun), wuguosong@hhu.edu.cn (G. Wu)

Abstract: High-strength Mg alloys have historically suffered from a challenge in achieving good ductility. Here, we report an asymmetric gradient nanostructure design prepared by ultrasonic severe surface rolling (USSR) at room temperature. Unlike conventional gradient-nanostructured materials that employ a hard-soft-hard sandwich structure, this new design incorporates a combined gradient distribution of grain microstructure and nanoprecipitates throughout the entire sample along the thickness direction. The nanoprecipitates are identified as the β-Mg17Al12 phase and are primarily generated through In-situ precipitation promoted by the USSR-induced high-density dislocations and temperature increment. Benefiting from this unique microstructure, an outstanding strength-ductility synergy is achieved, with a yield strength of 372.8 MPa, an ultimate tensile strength of 453.3 MPa, and an elongation of 11.5%. The enhanced strength can be attributed to several mechanisms, including grain boundary strengthening, dislocation strengthening, precipitation strengthening, twin strengthening, and hetero-deformation induced (HDI) strengthening. The HDI hardening and activation of multiple deformation modes also contribute to good ductility. This work provides a promising and effective method for overcoming the longstanding strength-ductility trade-off dilemma in Mg alloys.

Key words: Mg alloy, Strength-ductility synergy, Gradient nanostructure, Precipitates, AZ91