High performance gravity cast Al9Si0.45Mg0.4Cu alloy inoculated with AlB2 and TiB2

The primary alpha-Al grain size was 540 +/- 110 pm in the Al9Si0.45Mg0.4Cu alloy refined by conventional Al5Ti1B master alloy, and that was 340 +/- 80 gm in the Al3Ti3B refined alloy. The yield strength, tensile strength and elongation of the T6 heat treated alloy refined by Al3Ti3B were 320 +/- 2 MPa, 375 +/- 10 MPa and 6.0 +/- 1.0% respectively, which were increased by 3%, 4% and 50% in comparison with the alloy refined by Al5Ti1B. beta, Q' and theta' precipitates were verified for peak strengthening of the heat treated alloys. The majority of precipitates were beta and Q', while the minority was theta'. The volume of porosity was decreased by 50% in the Al3Ti3B refined alloy comparing with the Al5Ti1B refined alloy. The inoculation of AlB2 along with TiB2 results in the better grain refinement under Al3Ti3B, which contributes to the enhancement of yield strength and reduction of porosity. The improvement of tensile strength and ductility in Al3Ti3B refined alloy is attributed to the decrease of the size and area fraction of porosity on the fracture surface.