ISSUE 2/2009

/// 04
Masoumeh Faraji, Laurence Katgerman, Delft, The Netherlands
Grain refinement and modification in hypoeutectic Al-Si alloys

In this study the effect of alpha-aluminium grain refinement and eutectic silicon modification on the microstructure and cooling behaviour of a hypoeutectic Al-Si alloy individually and simultaneously was investigated, using Al-3Ti-B and Al-10Sr master alloys. The morphological observations and quantitative metallography showed that addition of 0.002 wt % titanium (as Al-3Ti-B) almost halved grain size of primary aluminium in an ingot of a commercial hypoeutectic Al-Si alloy, cast in a bar-shaped copper mould, whereas addition of 0.002 wt % titanium with 0.02 wt % strontium resulted in a decrease in this grain refinement, however, most of eutectic phase became modified. On the other hand, 0.02 wt % strontium modified almost all of the eutectic phase but had a slight refinement effect on primary aluminium phase.
Furthermore, in this study the individual and simultaneous effect of grain refiner and modifier on the incidence and size (area) of porosities was investigated quantitatively. On the basis of experimental observations and quantitative analysis, it was concluded that among four different samples of untreated sample, 0.002 wt % titanium-added sample, 0.02 wt % strontium-added sample, and 0.002 wt % titanium + 0.02 wt % strontium added sample, titanium treated sample gave the least porosity incidence in the alloy. It also decreased the size (area) of the pores down to three times, compared to untreated sample, whereas, adding strontium increased the incidence and size of casting pores, with and without presence of titanium.

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