EFFECT OF GRAIN-REFINEMENT ON THE FLUIDITY OF 2 COMMERCIAL AL-SI FOUNDRY ALLOYS

The effect of grain refinement on the fluidity of AlSi7Mg and AlSil1Mg has been investigated by spiral tests. Two different types of grain r efiners have been evaluated. An AlTi5B1 master alloy was added to diff erent Ti contents. Since the commercial alloys had a high initial cont ent of titanium, model alloys were made to investigate the fluidity at low grain refiner additions. Commercial alloys grain refined only by boron additions have also been investigated. The results from the flui dity measurements have been verified by measuring the dendrite coheren cy point of the different cast alloys. Although different, the two met hods show similar trends. The spirals from each fraction grain refiner cast were subsequently investigated metallographically at the tip of the spirals and at a reference point a distance behind, but no obvious difference in structure was observed. For both alloys, an increase in fluidity is observed as the content of grain refiner increases above 0.12 pet Ti, while the fluidity is impaired with increased grain refin ement below 0.12 pet Ti. The alloys grain refined with similar to 0.01 5 pet B show the highest fraction solid at dendrite coherency, the sma llest grain size, and the best fluidity.