Pistones

Journal of Materials Processing Technology 113 (2001) 486±492

An experimental study on the optimization of powder forging
process parameters for an aluminum-alloy piston
Jong-Ok Parka, Kil-Jun Kima, Dae-Yong Kanga,
Young-seog Leeb, Young-Ho Kima,*
a

b

School of Mechanical Engineering, Pusan National University, Pusan 609-735, South Korea
Plate, Rod and Welding Group, POSCO TechnicalResearch Laboratory, Pohang 790-785, South Korea

Abstract
The purpose of this paper is to optimize the powder forging process parameters for an aluminum-alloy piston, namely the composition,
mixing time, sintering time, sintering temperature, shape of the preform, etc., through experiments and to develop a high strength
aluminum-alloy piston with an optimized process.
At the ®rst step, thecomposition of the material was determined and optimal sintering conditions for the material were examined. Proper
mass percentages of Al, Cu, Si, Ni, Mn, Mg powders were added to Alumix 123 (Al±4.5Cu±0.5Mg±0.7Si), manufactured by Eckart
(Germany). The number of experimental parameters were totally 27, i.e., Si contents of 1, 1.5, 2.0% (mass), sintering temperatures of 560,
580 and 6008C, andsintering times of 20, 25 and 30 min. From the experiments, a Si content of 1.5% (mass), a sintering temperature of
5808C, and a sintering time of 25 min were determined as the optimal process conditions.
At the second step, the shape of preform for a cup-shaped product was determined considering the workability of the material and the
effect of density increase in the forging process.Performed for this purpose was the upsetting test for the workability of the sintered
specimens. The effect of density increase and strain loci were studied. A preform with a proper wall height was determined as the most
effective shape.
Finally, an aluminum-alloy piston for a vehicle engine was formed using the process parameters determined previously. After T6 heattreatment of the formed piston, thehardness and tensile strength of the piston head were examined. The results showed, that compared with
the hardness and tensile strength of the forged piston, those of the formed piston increased to 76.4 HRB and 500 MPa. # 2001 Elsevier
Science B.V. All rights reserved.
Keywords: Powder forging; Sintering; Preform design; Aluminum-alloy piston

1. Introduction
Generally, most vehicle enginepistons have been manufactured by die-casting, but, casting technology has limits
because of the rough cast microstructures and the weak
fatigue strength caused by internal defects, in spite of the
marked advances in technology. To overcome these demerits, the forging of a sintered metal-powder preform is
currently popular in many areas as an economic method
of producing mechanicalcomponents. Powder forging is
particularly attractive because it blends the cost and material-saving advantages of conventional castings and forgings
through better dimension and weight control. Powder forged
parts can even outperform parts machined from a forged
blank, probably as a consequence of fully dense, absolutely
*
Corresponding author. Tel.: ‡82-51-5102322; fax: ‡82-51-5147640.
E-mailaddress: kimyho@hyowon.pusan.ac.kr (Y.-H. Kim).

uniform and very ®ne grained microstructure. The powder
forged parts are typically made with zero draft as ¯ashless
closed-die forging in one blow, enabling forming, and
consequently reduced machining and material costs. Parts
containing through-holes and complex con®gurations
may be manufactured with little material loss, thus eliminatingsecondary processes such as trimming, machining,
or grinding [1].
A considerable amount of work has been reported
recently on the various technological aspects of the industrial processing of metal-powder forging [2±5]. Recently,
Iwata et al. [6] carried out investigations concerning a
powder forged piston using an extruded billet. Arnhold
and Muller-Schwelling [7] studied the applications of...