Dendrite arm spacing in aluminium alloy cylinder heads produced by gravity semi-permanent mold

Abstract

The goal of this work is to study the influence of process parameters upon DAS of cast aluminium cylinder heads. In the first step, in order to evaluate the effect of the chemical composition of the alloy, having a fixed casting geometry, we measured the DAS value upon:

• samples taken from specific simple-shaped castings;
• FIAT JTD cylinder head, that were chosen as reference castings
poured with three different alloys that are commonly used for cylinder head production at Teksid Aluminum.

The experimental results showed that increasing the content of alloying elements like silicon or copper brings to a reduction of DAS values.
In a second step, we studied the influence of process parameters which affect the solidification rate of real castings, like liquid metal temperature at pouring, mold temperature, and geometric configuration of the casting in the area of combustion chambers; we found that lower DAS values are obtained more easily by lowering the pouring temperature rather than mold temperature.
Finally, after studying DAS values of cylinder head casting having different geometries in the combustion chamber area, we found that DAS values in the combustion chamber area are lower when the casting solidification shrinkage is fed through the bolt bosses or the camshaft bearings, rather than through the spark plug towers or the fuel injector bosses.
All the samples were taken from the production of Teksid Aluminum plants which cast aluminium alloy cylinder heads in gravity semi-permanent mold technology.
The data obtained from this study will be used to improve process control, and to help the selection of the alloy and the design of the casting and of the gating/feeding system for future products.