Preparation of a novel Al–3B–5Sr master alloy and its modification and refinement performance on A356 alloy

•A novel Al–3B–5Sr master alloy has been prepared by in situ synthesis method.•Al–3B–5Sr can avoid the mutual poisoning effect between Sr and B to some extent.•Al–3B–5Sr has good grain refining and modification performance on A356 alloy. A novel Al–3B–5Sr master alloy has been prepared through in situ synthesis method in Al melt. The as-prepared master alloy was then used to modify A356 alloy. The microstructures of the Al–3B–5Sr alloy and modified A356 alloy were investigated. The results showed that the Al–3B–5Sr alloy mainly consisted of phases of α-Al and granular SrB6, while the Al–3B–5Sr–7Si alloy contained irregular blocky Al4Sr phase, AlB2 and Si besides the above-mentioned phases. Satisfactory grain refining and modifying effects were obtained by the addition of Al–3B–5Sr alloy (0.5wt.%) to the A356 alloy. Meanwhile, the morphology of eutectic silicon was changed from needle/platelike form to fibrous/globular form. The sizes of the α-Al dendrites decreased from ∼1000μm to ∼300μm. The mechanical properties of A356 alloy has been improved significantly with 0.5wt.% Al–3B–5Sr alloy addition.