Microstructure Characteristics and Its Effect on the Fracture in the Triple Junction Region of Friction Stir Welded Mg Alloys Subjected to Tension.

Guodong Liu,Yongshan Cheng,Qunying Yang

doi:10.3390/ma13173672

Abstract

Because of the tensile strength decreasing of the friction stir welded wrought magnesium (Mg) alloy compared to the base material, the reasons for the failure of weld has been focused on. After the fracture in transverse tension, the crack went through the welded joint from the center of the weld to the transition zone between the thermal-mechanical affected zone and weld zone. In the present study, the microstructure characteristics and its effect on the facture in the triple junction region is investigated. Based on the metallography and the electron back-scattered diffraction (EBSD) technology, it was observed that a twin band extended from the triple junction region to the middle of weld. The profuse twinning in the twin band was considered to play an important role on the crack propagation from the stir zone edge to the crown zone.

Highlights

As one of the lightest structural materials, magnesium (Mg) alloys have wide application in the aerospace and automotive industries for the purpose of weight saving [1]
Abundant twins were generated in the triple junction region at the stress level of 90% ultimate tensile strength (UTS)
It was observed that a boundary appeared between crown zone (CZ) and stir zone (SZ) on the fracture surface of weld

Summary

Introduction

As one of the lightest structural materials, magnesium (Mg) alloys have wide application in the aerospace and automotive industries for the purpose of weight saving [1]. As a solid-state joining technology, the friction stir welding (FSW) is useful for improving the joining of Mg alloys [3,4]. FSW has been successfully applicated in several Mg alloys systems, such as AZ (Mg–Al–Zn) and AM (Mg–Al–Mn) [5,6]. The FSW joints of wrought Mg alloys suffers usually from a problem of tensile strength decreasing, compared to basal metal [7,8,9,10]. The reasons for failure occurring in the regions of FSW Mg alloys have been focused on [14,15,16,17,18]

Methods

Discussion

Conclusion