Paper Title:
Thixoforming of Hypereutectic Al/Si Automotive Pistons
  Abstract

For hypereutectic Al/Si alloys, one of the advantages of thixoforming in comparison with casting routes is the relatively short processing times at high temperatures and hence limited coarsening of the Si phase. Coarse silicon particles give poor mechanical properties. Here two hypereutectic Al/Si alloys (magneto-hydro-dynamically (MHD) stirred A390 from Pechiney and an extruded A390 alloy from Showa in Japan) have been thixoformed to form pistons. Opening up the die entrance to the full width of the crown made the flow into the die more uniform and helped to reduce the tendency for large pores to form due to swirling of the slurry. Die heating reduced cold shuts in the skirt (thin section) of the piston. Placing inserts into the die to make holes for the piston pins (i.e. having an obstacle in the thicker regions) evened up the flow between the thick and the thin regions in the die. Massive pores experienced in earlier shots were then eliminated. Placing ceramic material in the die entrance considerably reduced the shrinkage porosity in the crown. The use of the Showa alloy, where the globular semisolid microstructure is achieved by a solid state deformation route rather than MHD, gave reduced shrinkage porosity and eliminated macrosegregation of the eutectic and the silicon. Computer modeling has aided optimization of the die.

  Info
Periodical
Solid State Phenomena (Volumes 141-143)
Edited by
G. Hirt, A. Rassili, A. Bührig-Polaczek
Pages
201-206
DOI
10.4028/www.scientific.net/SSP.141-143.201
Citation
H.V. Atkinson, P.J. Ward, "Thixoforming of Hypereutectic Al/Si Automotive Pistons", Solid State Phenomena, Vols. 141-143, pp. 201-206, 2008
Online since
July 2008
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Price
$32.00
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