Combined effect and its mechanism of Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr master alloy on microstructures of Al–Si–Cu alloy

The combined effect of Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr on Al–Si–Cu alloy has been investigated. Equiaxed dendritic grain of 100–120 μm was obtained with holding time of at least 240 min through addition of more than 0.020% Ti and 0.026% B, though the laminar morphology of eutectic Si kept unaltered. Eutectic Si was completely modified for more than 240 min through addition of Al–10wt.%Sr which also had some benefit on the refinement of primary α-Al. The combined addition of both Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr led to shorter working time of modification and slightly coarser grain size. The above results are mainly due to the formation of SrB6 through the reaction between Al–10wt.%Sr and Al–3wt.%Ti–4wt.%B. It was found that satisfactory grain refinement and modification could be attained by suitable addition of both Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr in spite of the formation of SrB6.