Abstract

Nb-based intermetallics contained in the master alloy act as potent heterogeneous nucleation substrate for the nucleation of primary Al dendrites. The addition of the 96Al–2Nb–2B master alloy to the LM25 alloy permits to significantly refine its microstructural features and the refinement is achieved in a great range of cooling rates. The formation of columnar grains at slow cooling rates is prevented.

Highlights

  • The refining treatment on hypo-eutectic Al–Si alloy is practically convenient and this is normally carried out by the addition of commercial master alloys developed on the Al–Ti–X ternary system (Mayes et al, 1993)

  • The Al–Ti–X commercial master alloys are highly effective in refining pure aluminium and wrought aluminium alloys due to both the nucleation potency of the Ti-compounds and the high growth restriction factor of titanium on aluminium

  • On increasing the silicon addition to aluminium, the grain size passes through a minimum that occur at 0.5–7 wt.% Si depending on conditions, but is typically ∼3–4 wt.% Si (Johnsson and Bäckerud, 1994)

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Summary

Introduction

Starting from the study of the addition of pure Nb and/or B on binary Al–Si alloys (Nowak et al, 2015) as well as commercial alloys (Bolzoni et al, 2015b), it was shown that their effect is much greater than addition of the individual elements (i.e. Nb or B alone) (Bolzoni et al, 2015c). In this manuscript the refining performances of one of these master alloys (i.e. the 96Al–2Nb–2B master alloy) on the microstructural features and mechanical properties of the hypo-eutectic LM25 (A356) alloy are addressed, presented and discussed in details

Methods
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