Research Papers

Experimental Study on Viscosity and Phase Segregation of Al–Si Powders in Microsemisolid Powder Forming

[+] Author and Article Information
Yufeng Wu

Department of Mechanical Engineering, Iowa State University, Ames, IA 50010andywu@iastate.edu

Gap-Yong Kim

Department of Mechanical Engineering, Iowa State University, Ames, IA 50010gykim@iastate.edu

Iver E. Anderson

Ames Laboratory, US Department of Energy, Ames, IA 50010andersoni@ameslab.gov

Thomas A. Lograsso

Ames Laboratory, US Department of Energy, Iowa State University, Ames, IA 50010lograsso@ameslab.gov

J. Manuf. Sci. Eng 132(1), 011003 (Dec 28, 2009) (7 pages) doi:10.1115/1.4000636 History: Received January 19, 2009; Revised November 05, 2009; Published December 28, 2009; Online December 28, 2009

Semisolid powder forming is a promising approach for near-net shape forming of features in macro-/microscale. In this paper, viscosity and phase segregation behavior of Al–Si powders in the semisolid state were studied with back extrusion experiments. The effects of process parameters including shear rate, extrusion ratio, heating time, and precompaction pressure were analyzed using the design of experiments method. The results showed that the effects of shear rate, extrusion, ratio and heating time were statistically significant factors influencing the viscosity. The semisolid state powders showed a shear thinning behavior. Moreover, microstructure analysis of extruded parts indicated severe phase segregation during the forming process. As the extrusion opening became small (400μm), the phase segregation increased. This study expanded the semisolid processing technology by exploring the use of powdered materials instead of typical bulk materials for applications in micro-/mesomanufacturing. Replacing bulk materials with powdered materials may add a new dimension to the technique by allowing tailoring of material properties.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Comparison between bulk semisolid forming and semisolid powder forming

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Figure 2

Process routes of various semisolid powder forming

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Figure 3

Setup for back extrusion of semisolid powders

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Figure 4

Original Al–50Si powder used in the experiments

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Figure 5

Phase diagram of Al–Si binary alloy system

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Figure 6

Microstructures at different locations of a back extruded part (run No. 11 in Table 2)

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Figure 7

Typical force-displacement during back extrusion of semisolid Al–50Si powders (run No. 1 in Table 2)

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Figure 8

Mean values of viscosity at different parameter levels  *: precompaction pressure

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Figure 9

Mean value of phase segregation at different parameter levels

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Figure 10

Optical images showing the growth of Si grains with increasing heating time: (a) 20 min heating (run No. 1) and (b) 40 min heating (run No. 11) at location D

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Figure 11

Silicon fraction at different positions in the samples: part (a) is fabricated with λ=6.12 and γav̇=100 and (b) λ=6.12, and γav̇=20; darker area and bright area mean either high Si concentration or Al concentration, respectively



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