Fabrication of In-Situ BaB ₆/Al Composites and Their Refining and Modifying Effect on A356.2 Alloy

Abstract

In this work, as an inoculant, in-situ BaB₆/Al composites was successfully fabricated and used to refine α-Al dendrites and modify eutectic Si of A356.2 alloy. BaB₆/Al ingot and ribbon composites mainly contain two phases, α-Al and BaB₆. In BaB₆/Al ribbons, nano-size BaB₆ ceramic particles exist and disperse uniformly which help to better exert the inoculant effect in A356.2 alloy. When 2.0% BaB₆/Al ribbons were added (B4 alloy), A356.2 alloy achieved the best effects. YS, UTS, EL and HV of B4 alloy are respectively 36.3%, 18.3%, 46.4% and 20.8% higher than A356.2 alloy (B0). Moreover, BaB₆/Al ribbons which has nanoparticles present much better mechanical properties than ingots at the same addition amount. With BaB₆/Al composites addition, the fracture features change significantly from brittle fracture to ductile fracture. Al and BaB₆ form the clear and stabile BaB₆/Al interface, thereby facilitating heterogeneous nucleation and grain refinement for A356.2 alloy. They have low interface crystallographic mismatch and some orientation relationships (ORs). The combined of free micro-alloying elements Ba and B in BaB₆/Al composites eventually promote the forming of twins which lead to fine fibrous and granular Si.

Keywords: A356.2, BaB6/Al Composites, Refine and Modify, Mechanical Properties, BaB6/Al Interface, Si Twins