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Abstract
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.
Highlights
The grain refinement of light alloys via chemical inoculation, for example wrought Al alloys by means AlTiB master alloys, has been extensively studied over the last decades aiming to comprehend the mechanism governing the grain refinement and optimise the inoculation process for its industrial use as well as to develop new grain refining compositions [1e3]
AlTiB master alloys have lower grain refining ability in foundry alloys, such as AlSi alloys with Si > 3%, as the potency of the Ti-based particles is annihilated by the presence of Si, a phenomenon known as poisoning [4e8]
The XRD patter of Fig. 1f), which is representative for all the Al2NbxB master alloys regardless of their manufacturing route, confirms the phase identified via microstructural analysis
Summary
The grain refinement of light alloys via chemical inoculation, for example wrought Al alloys by means AlTiB master alloys, has been extensively studied over the last decades aiming to comprehend the mechanism governing the grain refinement and optimise the inoculation process for its industrial use as well as to develop new grain refining compositions [1e3]. AlTiB master alloys have lower grain refining ability in foundry alloys, such as AlSi alloys with Si > 3% (compositions are in wt.% if not specified differently), as the potency of the Ti-based particles is annihilated by the presence of Si, a phenomenon known as poisoning [4e8]. Chemical inoculation of AlSi alloys by means of AlB master alloys has received renewed attention by the scientific community in recent years aiming to understand the potency of AlB master alloys, both in pure Al [10] and foundry AlSi alloys [11], and clarify the mechanism governing the refinement [12]. Reason behind being the fact that, thermodynamically, Ti boride is more stable than Al borides [14] and over time, the latter will transform into the former if Ti is present
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