Effects of La–Ce addition on microstructure and mechanical properties of Al–18Si–4Cu–0.5Mg alloy

Abstract The microstructural evolution and mechanical properties of Al–18Si–4Cu–0.5Mg alloy modified by the addition of La–Ce rare earth elements through OM, SEM, EPMA and tensile tests were investigated. The results of OM and SEM analyses indicated that primary Si particles were significantly refined from coarse block-like and irregular polygonal shapes into fine flaky shapes, while eutectic Si particles were modified from coarse and needle-like into fine and rod- or coral-like shapes with increase of La–Ce addition. The alloy exhibited the minimum primary Si particle size and the best mechanical properties with the addition of 0.3 wt.% La–Ce. The average particle size decreased from 61 to 28 μm, the ultimate tensile strength increased from 222 to 242 MPa and the elongation increased from 3.2% to 6.3%. In addition, modification mechanisms and fracture modes were explored by the means of SEM and EPMA.