Research Papers

Microstructural Assessment of Copper Friction Stir Welds

[+] Author and Article Information
A. Polar

Department of Materials Engineering, University of Illinois at Chicago, Chicago, IL 60607apolar@uic.edu

J. E. Indacochea

Department of Materials Engineering, University of Illinois at Chicago, Chicago, IL 60607jeindaco@uic.edu

J. Manuf. Sci. Eng 131(3), 031012 (May 20, 2009) (7 pages) doi:10.1115/1.3123313 History: Received February 02, 2006; Revised February 03, 2009; Published May 20, 2009

Friction stir welding (FSW) of electrolytic tough pitch copper plates was conducted using a conventional CNC milling machine. The microstructure evolution of the weld was correlated with the process parameters used in the study and in conjunction with increasing temperatures during processing. When the optimum process parameters were achieved, a sound weld joint was obtained. The weldments were evaluated by microstructural analysis, using optical and scanning electron microscopes, and in terms of mechanical properties. At early stages of FSW and/or when using less than optimum welding parameters low temperatures result, metal does not plasticize effectively producing defects, such as large cavities, porosity, and poor bonding, due to the lack of plasticized material. Cavities were found at the advancing region of the weld, and in this area the finest grains were observed from the entire weld. The cavities were reduced, and the grain size increased further along in the weld as the temperature increased also. The typical weld nugget found in the friction stir welding of other metals was not observed in this case. Dynamic recrystallization was observed in the “stirred zone” of the weld; considering that the strain rate in this region was the same in all three cases, the difference in grain size was attributed to the differences in process temperature.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Effect of temperature on the tensile strength of Al 6061-T6 and Cu 10100–0 (23)

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Figure 2

Typical microstructure of the annealed copper plate used as parent metal in this investigation

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Figure 3

External aspect of the weld showing the points were temperatures were collected. Notice the oxidation progress at the surface.

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Figure 4

Macrograph of the weld cross sections related to (a) cold copper weld, (b) warm copper weld, and (c) hot copper weld

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Figure 5

Micrograph of the interface between the stirred zone (small grains) and the TMAZ (larger grains) at the advancing side of the cold weld sample

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Figure 6

Micrograph showing the fine grain structure in the stirred zone of the cold weld sample

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Figure 7

Grain size evolution with temperature

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Figure 8

Micrograph of the TMAZ-stirred zone interface at the advancing side of the warm weld sample. Notice that the finer grains are found just at the interface.

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Figure 9

TMAZ-stir zone interface at the advancing side in the hot weld

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Figure 10

TEM micrograph of a DRX grain in an area close to the cavity in a cold sample

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Figure 11

Stress-strain curves for the parent metal and FSW ETP copper samples

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Figure 12

SEM micrographs of (a) fracture surface of FS weld and (b) parent metal tensile samples. Notice the amount of ductile fracture is larger in the case of the parent metal (b).




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