Microstructure Distribution and Tensile Anisotropy of Dissimilar Friction Stir Welded AM60 and AZ31 Magnesium Alloys

doi:10.1007/s40195-020-01111-2

摘要/Abstract

Abstract:

The microstructure distribution, tensile anisotropy and fracture behaviors in the dissimilar friction stir welded joint of AM60/AZ31 alloys were investigated. Experimental results showed that a significant grain refinement and an orientation fluctuation occurred in the weld. The grain size of AZ31 side in joint was obviously smaller than that of AM60 side. There was a higher percentage of low angle grain boundaries (LAGBs) and a lower degree of recrystallization in AZ31 side compared with those in AM60 side, especially for the thermo-mechanically affected zone in AZ31 side. The discrepancies of grain size distribution, recrystallization behavior and LAGBs in joint depended on the different initial state of two metals and the inhomogeneous temperature distribution in joint. In addition, the (0001) basal plane in weld was roughly parallel to the surface of the pin, showing the symmetrically distributed texture characteristics. The joint showed an obvious tensile anisotropy due to the special texture distribution. The comprehensive tensile properties of joint along the three directions decreased in the order: welding direction, 45° direction and transverse direction. The maximum ultimate tensile strength, yield strength and elongation of the joint were 242 MPa, 116 MPa and 21.2%, respectively. The fluctuations of grain size and texture in joint affected the fracture behavior of samples in the three directions.

Key words: Friction stir welding, Dissimilar joint, Texture, Anisotropy, Tensile properties

. [J]. 金属学报英文版, 2020, 33(11): 1487-1504.

Jun-Lei Zhang, Han Liu, Yu-Lu Xie, Guang-Sheng Huang, Xiang Chen, Bin Jiang, Ai-Tao Tang, Fu-Sheng Pan. Microstructure Distribution and Tensile Anisotropy of Dissimilar Friction Stir Welded AM60 and AZ31 Magnesium Alloys[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(11): 1487-1504.

图/表 21

Fig. 1 Schematic illustration of FSW a illustration of sample preparation for tensile test b

Fig. 2 Cross-sectional morphologies of the FSW joint: a AM60/AZ31 joint; b AZ31/AM60 joint

Fig. 3 Inverse pole figures of various regions of the AM60/AZ31 joint

Fig. 4 Grain size distributions of the AM60/AZ31 joint a; force diagram of TMAZ during FSW b

Fig. 5 AZ31 metal a; AM60 metal b of the AZ31/AM60 joint

Fig. 6 Grain boundary maps, misorientation angle distributions and grain morphology maps of BMs: a AM60; b AZ31

Fig. 7 Grain boundary maps, misorientation angle distributions and grain morphology maps of TMAZs: a AS; b RS

Fig. 8 Grain boundary maps, misorientation angle distributions and grain morphology maps of NZ: a NZ side of AS; b NZ side of RS; c NZ center

Fig. 9 Schematics of the welding process: a schematic illustration of the FSW process in NZ; b schematic illustration of the shear layer formation induced by motion of the FSW tool

Fig. 10 Texture distributions in various regions of the AM60/AZ31 joint

Fig. 11 a Stress-strain curves ; b fracture morphology of the AM60/AZ31 joints

Table 1 Tensile properties of the joint in the three directions

Samples	YS (MPa)	UTS (MPa)	EI (%)
TD	116±2.9	216±1.5	5.9±0.6
45°	109±2.6	227±3.1	9.2±0.4
WD	100±1.8	242±1.2	21.2±0.5

Fig. 12 Fracture morphologies of three types of tensile samples: a , d TD; b ,e 45°; c , f WD

Fig. 13 Dislocation density mapping based on the EBSD data in a AM60, b TMAZ of AS, c NZ side of AS, d AZ31, e TMAZ of RS, f NZ side of RS

Fig. 14 SFs distributions in various regions of the joint: (0001) pole figures show the calculated SF for basal slip

Fig. 15 SFs distributions in various regions of the joint: (0001) pole figures show the calculated SF for extension twinning

Fig. 16 Mean SF values in various regions for a basal slip ; b extension twinning

Fig. 17 EBSD maps of WD samples after fracture: a kernel average misorientation map; b grain boundary map

Fig. 18 OM and EBSD maps of a TD ;b 45° samples after fracture

Fig. 19 SEM images showing second phases: a AZ31 BM; b NZ; c AM60 BM

Fig. 20 a 45° samples before fracture, b OM ;c EBSD maps of joint bottom

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