Effects of La addition on the microstructure and tensile properties of Al-Si-Cu-Mg casting alloys

The effects of La addition on the microstructure and tensile properties of B-refined and Sr-modified Al-11Si-1.5Cu-0.3Mg casting alloys were investigated. With a trace addition of La (0.05wt%-0.1wt%), the mutual poisoning effect between B and Sr can be neutralized by the formation of LaB₆ rather than SrB₆. By employing a La/B weight ratio of 2:1, uniform microstructures, which are characterized by well refined α-Al grains and adequately modified eutectic Si particles as well as the incorporation of precipitated strengthening intermetallics, are obtained and lead to appreciable tensile properties with an ultimate tensile strength of 270 MPa and elongation of 5.8%.