Effect of Al5Nb0·5B master alloy on grain refinement and mechanical properties of Al7Si alloy

Al5Nb0.5B as a kind of novel master alloy, the influencing mechanisms of 0.2wt% Al10Sr combined with varying contents of Al5Nb0.5B master alloy on the microstructure, grain refinement, and mechanical properties of Al7Si alloys were investigated. The results proved that 0.2wt% Al10Sr master alloy addition modified the morphology and changed its growth pattern of eutectic Si particles. Further addition of Al5Nb0.5B master alloy content decreased the average α-Al grain size by 60.8 %, reduced the average secondary arm dendrite spacing (SADS) by 43.6 %, and the number and size of β iron phases in refined Al7Si alloys also decreased. Al 3 Nb and NbB 2 particles proved to demonstrate high nucleation potency for the primary α-Al in modified Al7Si alloys. Increased addition of Al5Nb0.5B master alloy further influenced the melting and solidifying process, inhibited the α-Al grains’ nucleation and growth. The mechanical properties of modified Al7Si alloys improved with Al5Nb0.5B master alloy addition, micro hardness improved max about 5 HV, ultimate tensile strength (UTS) increased from 154 MPa to 165 MPa, and the elongation (EI) value improved from 18.3% to highest 24.3%. The fracture mode changed from the main brittle fracture to ductile fracture.