ELSEVIER December 1996 Materials Letters 29 (1996) 209-213 Oxide film casting defects in squeeze composites cast metal matrix Adam Papworth, Peter Fox zyxwvutsrqponmlkjihgfedcbaZYXWVUT The Department of Materials Science, The ZJnil;ersiQ of Li[‘erpool. * Liverpool, L69 3BX, UK Received 8 February 1996; revised 4 June 1996; accepted 5 June 1996 Abstract Squeeze casting is a commonly zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA use d method of producing metal matrix composites (MMC’S). It is especially popular in the automotive industry for the production of pistons for diesel engines. This paper describes a casting defect associated with the production of metal matrix composites by this method. The mechanism of formation of the defect is considered and its effect on the future of squeeze casting considered. Keywords: Squeeze casting; Metal-matrix composites; Casting defects 1. Introduction Squeeze casting is now a well-developed tech- nique for the production of metal-matrix compos- ites. It is used in the automotive industry for the production of pistons for diesel engines [ll where an annular ceramic preform is cast into the top of the piston to increase the hot fracture resistance. A second use of MMC’s in pistons is developing, with the replacement of steel piston ring carriers. These rings are annular sections cast into the piston so as to reinforce the top piston ring slot. The disadvantage with the steel rings is that they are not strongly bonded into the casting and if placed too near the top of the piston can come loose, destroying the engine, whereas if the rings are placed low down on the piston unburnt hydrocarbons are trapped, * Corresponding author. creating greater pollution. However, if MMC rings are used to replace the traditional steel rings, they can be safely placed nearer the crown of the piston, as they are less likely to come adrift. This use of MMC’s is much more severe and pistons sometimes fail at the interface between the unreinforced and reinforced regions. The pistons are normally produced from a piston alloy, for example AE109 (Al, 12 wt% Si, 1 wt% Ni, 1 wt% Cu, 1 wt% Mg) alloy. The alloy is used because it has high dimensional stability at the high temperatures reached during use. The ceramic pre- forms are normally produced from either Saffil, a S-Al,O, fibre, or from fibres made from aluminosili- cate. To retain the shape of the preform during casting a binder is used, normally silica. When pistons are produced by squeeze casting, the preform is retained in the mould. This stops it floating when the aluminium alloy is added. The molten alloy is poured into the mould either by hand 00167-577X/96/$12.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved. PII SOl67-577X(96)00148-6