On the grain refining efficacy of Ti-free hypoeutectic AlSi via AlTiB, AlB and AlNbB chemical inoculation

Metals with a fine grain structure have intrinsic advantages like higher mechanical strength and more isotropic behaviour. An effective way of refining the grain size is via chemical inoculation. In this study the grain refining efficacy of AlTiB, AlB and AlNbB master alloys on a Ti-free AlSi alloy is investigated. In particular, the performance of commercial Al5Ti1B and Al5B master alloys is compared to that of a lab-made Al2Nb2B and two Al2NbxB (x = 1 and 2 wt%) made in an industrial pilot scale facility. Although chemical inoculation does not change the morphology of the grains, which is always equiaxed dendritic, it is found that the grain size progressively decreases with the master alloy addition rate and the achievable final grain size is strongly dependent on the chemistry of the master alloy used. The experimental results demonstrate that AlNbB > AlB > AlTiB in terms of grain refining efficacy. (C) 2019 The Authors. Published by Elsevier B.V.