Effect of Zener-Hollomon Parameter on Microstructure and Mechanical Properties of Copper Subjected to Friction Stir Welding

doi:10.1007/s40195-019-00943-x

Abstract

Abstract:

In this work, the influence of the Zener-Hollomon (Z) parameter on the microstructure and mechanical properties of copper subjected to friction stir welding (FSW) was investigated. Liquid N₂ cooling was conducted to control the cooling rate after the FSW. The obtained results demonstrate that the Z parameter was dependent on the tool rotation rate during the FSW, i.e., a higher tool rotating rate resulted in a lower Z parameter. The grain size in the stir zone decreased with the increase in the Z parameter. The relationship between the yield strength and the Z parameter is established as σ_0.2 = σ₀ + kZⁿ. This relationship exhibited two different plots under the conditions of air cooling and liquid N₂ cooling. Even at a similar Z parameter, a significant yield strength difference occurred because massive dislocations, which were caused by the prevention of the post-annealing effect, were maintained in the stir zone. This study suggests that the influence of the post-annealing effect should not be neglected when analyzing the relationship between the Z parameter, microstructure, and mechanical properties.

Key words: Copper, Friction stir welding, Microstructure, Mechanical properties

Nan Xu, Ruo-Nan Feng, Wen-Feng Guo, Qi-Ning Song, Ye-Feng Bao. Effect of Zener-Hollomon Parameter on Microstructure and Mechanical Properties of Copper Subjected to Friction Stir Welding[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(2): 319-326.

Figures/Tables 12

Table 1 Tool material and dimensions used in this study

Table 2 A summary of the welding conditions for the FSW experiment

Fig. 1 Schematic of the RC-FSW process and cutting position of the tensile specimen. The welding direction, transverse direction, and plate-normal direction are indicated by WD, TD, and ND, respectively

Fig. 2 Inverse pole figure (IPF) maps of a the BM, and the SZ centers of the b 1#, c 2#, d 3#, e 4#, f 5#, g 6#, h 7# joints, respectively

Fig. 3 Misorientation angle distribution of a the BM, and the SZ centers of the b 1#, c 2#, d 3#, e 4#, f 5#, g 6#, h 7# joints, respectively

Table 3 Vickers hardness and tensile properties of the BM and SZs obtained by different welding conditions

Fig. 4 Bright field TEM images of the SZ obtained by a C-FSW (1#), b RC-FSW (7#)

Fig. 5 Variations of a the strain rate, b the peak temperature under different welding conditions

Fig. 6 Relationship between the grain size of the SZ and Z parameter obtained under different welding conditions

Fig. 7 Relationship between the grain size and the YS of the SZ obtained under different welding conditions

Fig. 8 Variations of the measured YS with Z parameter

Fig. 9 High-resolution TEM image with selected-area election diffraction of the stacking fault in the tensile-tested SZ obtained by RC-FSW (7#)

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