EVALUATION OF THE EFFECT OF MODIFIERS AND REFINERS ON THE MECHANICAL BEHAVIOR AND SHRINKAGE OF AL7SIXMG ALLOYS

摘要

1. Titanium as a grain refiner does not enhance the mechanical properties. 2. Strontium and sodium are both effective modifying agents for hypoeutectic alloys. However, strontium retains its modifying action much longer than sodium. 3. The quick fading of Na leads to a marked decrease of elongation. 4. Initial strontium amounts of 0.2 and 0.15% are not recommended. These high contents of Sr will cause overmodification which has a negative effect on the mechanical properties (strength). 5. An initial content of 0.02% Sr gives significant improvement in the elongation that remains high and nearly constant for 3 h in spite of a continual loss of Sr. 6. The modifying effect of strontium (for 0.02%) actually appears to improve slightly with holding time since the best elongation is obtained 90 min after the initial addition. 7. The simultaneous use of Na-Ti or Sr-Na does not lead to substantial improvement of the mechanical properties. 8. The treatment with Ti, Na and Sr decreases the macro shrinkage markedly. Strontium is the most effective to counteract top macro shrinkage. On the other hand, the combination Na-Ti (followed by Sr) leads to the smallest lateral macro shrinkage.