Development of an efficient grain refiner for Al–7Si alloy and its modification with strontium

Abstract

The grain refining response of Al and Al–7Si alloy has been studied with various Al–Ti, Al–B and Al–Ti–B master alloys at different addition levels. The results show that Al–B and B rich Al–Ti–B master alloys cannot grain refine Al, while they are efficient grain refiners to Al–7Si alloy. The level of grain refinement saturates after 0.03% of Ti or B for most of the master alloys studied both at short and long holding times. The grain refining efficiency of some elements other than Ti and B on Al–7Si alloy has also been studied. Interestingly, all the elements studied (B, Cr, Fe, Mg, Ni, Ti and Zr) have resulted in some grain refinement of Al–7Si alloy at short holding time and have shown fading/poisoning on long holding, which increased in the order of B (no poisoning), Ti, Cr, Ni, Fe, Mg, Zr. Sr (0.02%) has been found to provide complete modification of the eutectic in Al–7Si alloy within 2 min, which is not lost even after long holding up to 120 min. Significant improvements in the mechanical properties have been obtained by a combination of grain refinement and modification to an extent that was not possible by either of them alone.