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Research Papers

Effect of Pin and Shoulder Geometry on Stir Zone and Mechanical Properties of Friction Stir Spot-Welded Aluminum Alloy 2024-T3 Sheets

[+] Author and Article Information
Moslem Paidar

Department of Materials Engineering,
South Tehran Branch,
Islamic Azad University,
P.O. Box 14515/775,
Tehran 1866113118, Iran

Farzad Sadeghi

Department of Materials Engineering,
Science and Research Branch,
Islamic Azad University,
P.O. Box 14515/775,
Tehran 1477893855, Iran

Hamidreza Najafi

Assistant Professor
Department of Materials Engineering,
Science and Research Branch,
Islamic Azad University,
P.O. Box 14515/775,
Tehran 1477893855, Iran
e-mails: hnajafi@srbiau.ac.ir; hnajafi1@gmail.com

Ali Reza Khodabandeh

Assistant Professor
Department of Materials Engineering,
Science and Research Branch,
Islamic Azad University,
P.O. Box 14515/775,
Tehran 1477893855, Iran

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received December 18, 2014; final manuscript received March 13, 2015; published online April 16, 2015. Assoc. Editor: Peter W. Chung.

J. Eng. Mater. Technol 137(3), 031004 (Jul 01, 2015) (6 pages) Paper No: MATS-14-1254; doi: 10.1115/1.4030197 History: Received December 18, 2014; Revised March 13, 2015; Online April 16, 2015

Friction stir spot welding (FSSW) was performed on 2024-T3 Al alloy to study the effect of pin and shoulder geometry (cylindrical and triangular shapes) on stir zone (SZ) characteristics and mechanical properties of welded samples. The process was conducted at a constant dwell time of 5 s and shoulder plunge depth of 0.3 mm. The rotational speed varied in the range of 630–1600 rpm. Based on the observations, the change in the pin shape led to changes in the SZ area, hook geometry, and mechanical properties of the joints. At low rotational speeds, the strengths of the joints made by the triangular pin were higher than those formed by the cylindrical pin. On the other hand, the change in the shoulder geometry from cylindrical to triangular reduced the joint strengths. However, the effect of pin geometry on the strengths was more than the shoulder geometry. Moreover, the strengths were directly related to the SZ area. Scanning electron microscopy of the welded sections revealed formation of cracks in the SZ as a result of S phase local melting at the tool rotational speed of 1600 rpm.

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References

Figures

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Fig. 1

Schematic representation of FSSW process: (a) plunging, (b) stirring, and (c) drawing out

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Fig. 2

Microstructure of as-received Al 2024-T3 sheets

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Fig. 3

Schematic illustration of tensile shear specimen

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Fig. 4

Tools geometries and dimensions: (a) the cylindrical shoulder and pin (CC), (b) the triangular shoulder and cylindrical pin (TC), and (c) the cylindrical shoulder and triangular pin (CT)

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Fig. 5

Microstructure of different zones in a joint created by the CC tool: (a) SZ, (b) TMAZ, and (c) HAZ

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Fig. 6

The SZ microstructure formed by (a) the CC tool at rotational speed of 630 rpm, (b) the CT tool at rotational speed of 630 rpm, (c) the CC tool at rotational speed of 1600 rpm, and (d) the CT tool at rotational speed of 1600 rpm

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Fig. 7

(a) Cracks in the SZ formed by the CC tool at the rotational speed of 1600 rpm and (b) higher magnification of indicated area in (a) along with the result of EDS

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Fig. 8

Cross-sectional macrostructures of joints formed by the CC and TC tools

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Fig. 9

Cross-sectional macrostructures of joints formed by the CC and CT tools

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Fig. 10

Hooks formed by the (a) CC tool, (b) CT tool, and (c) TC tool

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Fig. 11

Tensile shear strength as a function of rotational speed

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Fig. 12

Macrostructure of a fractured tensile specimen showing propagation path of a crack

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Fig. 13

Microhardness profile of the joints formed by the CC and CT tools at rotational speed of 630 rpm

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