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Research Papers

Simulation of Material Flow and Heat Evolution in Friction Stir Processing Incorporating Melting

[+] Author and Article Information
H. W. Nassar

Masdar Institute of Science and Technology, Masdar City, P.O. Box 54224, Abu Dhabi, United Arab Emirateshnassar@masdar.ac.ae

M. K. Khraisheh

Masdar Institute of Science and Technology, Masdar City, P.O. Box 54224, Abu Dhabi, United Arab Emirates

J. Eng. Mater. Technol 134(4), 041006 (Aug 24, 2012) (7 pages) doi:10.1115/1.4006918 History: Received August 08, 2011; Revised March 26, 2012; Published August 24, 2012; Online August 24, 2012

Friction stir processing (FSP) is a relatively new technology for microstructure refinement of metallic alloys. At high processing speeds, excessive heating due to severe plastic deformation and friction may result in local melting at the interface between the FSP tool and the workpiece. In this work, a computational fluid dynamics (CFD) approach is applied to model material flow and heat evolution during friction stir processing of AZ31B magnesium alloy, taking into consideration the possibility of local melting in the stirring region. This is achieved by introducing the latent heat of fusion into an expression for heat capacity and accounting for possible effects of liquid formation on viscosity and friction. Results show that the temperature in the stirring region increases with the increase in rotational speed and drops slightly with the increase in translational speed. As liquid phase begins to form, the slope of temperature rise with rotational speed decreases and the maximum temperature in the stirring region stabilizes below the liquidus temperature at high rotational speeds. It is also shown that the formation of a semi-molten layer around the tool may result in a reduction in the shearing required for microstructure refinement.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic drawing of friction stir processing

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Figure 2

Finite element mesh of the FSP model

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Figure 3

Temperature contours in the stirring region for ω = 1200 rpm and vi  = 22 ipm

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Figure 4

Variation in maximum and average temperatures in the stirring region with (a) rotational speed and (b) translational speed

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Figure 5

(a) Streamlines A , B , and C of flowing material and (b) temperature history profiles extracted from streamlines A , B , and C compared to experimental observations by Darras [10]

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Figure 6

Variation of temperature in the stirring region with rotational speed in two models; the first considers liquid phase formation in response to excessive heating, while the second treats the material as a single-phase pure solid

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Figure 7

Isosurfaces of the volume fraction of liquid phase in the stirring region for a translational speed of 22 ipm and rotational speeds of (a) 500 rpm, (b) 800 rpm, (c) 1100 rpm and (d) 1400 rpm

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Figure 8

Effective heat capacity and the corresponding liquid fraction in the stirring region for ω = 1200 rpm and vi  = 22 ipm

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Figure 9

Variation in Qvisc and the average value of fl at the pin/workpiece interface with rotational speed

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Figure 10

Variation in Qfr and the average value of fl at the shoulder/workpiece interface with rotational speed

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Figure 11

Flow velocity in the x-direction along line A -B for rotational speeds of 400 rpm and 1200 rpm

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