Influence of Test Temperature on the Tensile Properties along the Thickness in a Friction Stir Welded Aluminum Alloy

doi:10.1016/j.jmst.2015.07.005

Abstract

Abstract: The aim of this study was to evaluate microstructures and the influence of test temperature on the tensile properties, strain hardening behavior and fracture characteristics of friction stir welded (FSWed) 2219-T62 aluminum alloy thick plate joints. A fine and equiaxed recrystallized grain structure had no significant change in grains at the top of weld nugget zone (WNZ) at a rotational rate of 500 r/min compared with 300 r/min, but the grains and second-phase particles at the middle of WNZ exhibited obvious coarsening. The yield strength, ultimate tensile strength and joint efficiency were observed to decrease with increasing test temperatures. However, the elongation presented a contrast trend. Compared with the middle and bottom slices, the top slice (216 and 342?MPa) had a higher strength and a lower elongation (8.5%) at different test temperatures. Hardening capacity and strain hardening exponent of bottom slices were higher than those of the top and middle slices. Both of them at room temperature (RT) were bigger than those at higher temperature (HT) and lower temperature (LT). The FSWed joints basically failed in the border area between the thermo-mechanical affected zone (TMAZ) and heat-affected zone (HAZ) of the top slice, and in the HAZ of the middle or bottom slices, while the fracture surfaces exhibited dimple fracture characteristics at different test temperatures.

Key words: Friction stir welding, Aluminum alloy, Microstructure, Tensile properties, Strain hardening, Test temperature

Weifeng Xu, Jinhe Liu, Daolun Chen. Influence of Test Temperature on the Tensile Properties along the Thickness in a Friction Stir Welded Aluminum Alloy[J]. J. Mater. Sci. Technol., 2015, 31(9): 953-961.

Figures/Tables 12

Cross-sectional macrostructures of FSW 2219Al-T62 joints. AS—

advancing side, RS—

retreating side.

Second-phase particles at top, middle and bottom along thickness in weld nugget zone with water cooling at rotational rates of 300 r/min (a, c, e) and 500 r/min (b, d, f).

Stress vs strain curves of 2219 alminum alloy BM and different slices of FSWed joint made at a rotational rate of 300 r/min (a) and 500 r/min (b) with water cooling tested at different test temperatures.

Effect of rotational rate on YS (a), UTS (b), and elongation (c) of BM and the top, middle, bottom slices of FSWed samples with water cooling during FSW at different tensile temperatures.

Effect of rotational rate on joint efficiency at different temperatures for the top, middle, bottom slices of FSWed samples with water cooling.

Effect of tensile temperature on the hardening capacity of the BM and top, middle and bottom slices of 2219 aluminum alloy FSWed joints with water cooling at different rotational rates.

Effect of tensile temperature on the strain hardening exponent of the BM and top, middle and bottom slices of FSWed 2219 aluminum alloy joints with water cooling at different rotational rates.

Strain hardening rate (θ

) vs net flow stress (σ

?σ

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