Grain refinement and tensile properties improvement of aluminum foundry alloys by inoculation with Al–B master alloy

The grain refining responses of Al–Zn, Al–Cu, Al–Mg and Al–Si binary systems to inoculation of Al–B master alloy were investigated quantitatively. At an addition level of 0.01 vol.% AlB2, Al–B master alloy failed to serve as an efficient grain refiner in refining the former three despite its preferred performance in refining Al–Si alloys. This cannot be explained by the eutectic reaction mechanism, which seems to be very plausible in recent studies. Further study in the viewpoint of solute paradigm provides an alternative understanding of the grain refinement mechanism by inoculation with Al–B master alloy. It appears that the refining potency of AlB2 particles could be enhanced when solute Si is present in the aluminum melt. The potential of Al–B master alloy in the grain refinement of AlSi7Mg, AlCu8Si and AlZn5Mg foundry alloys was investigated based on this finding. Tests of tensile properties have shown good agreement with the foregoing grain refinement studies. Al–B master alloy can be used as powerful grain refiner for AlSi7Mg alloy, and for AlCu8Si alloy only when casting is made shortly after grain refiner addition. For AlZn5Mg alloy, however, Al–B master alloy does not supply sufficient grain refinement as the case for aluminum alloys containing high contents of Si.