The characteristics of microstructure and dry sliding wear behavior of Al-11%Mg2Si hypoeutectic alloy with different La addition levels were systematically investigated by means of by a pin-on-disk wear testing machine, OM, SEM, and EDS. The results revealed that the addition of La obviously refined eutectic Mg2Si crystals in the alloy, and the average length ( \(L{\text{Mg}}2{\text{Si}}\) ) and interlamellar spacing (ILS) of the eutectic Mg2Si crystals apparently diminish from 40.1 and 2.7 μm without La to 25.2 and 1.2 μm after adding 0.4 wt.% La. Meanwhile, the shape of the eutectic Mg2Si in the alloy can be remarkably changed from coarse plate-like structures into fine granular or fibrous features. The refinement and modification of eutectic Mg2Si can be attributed to the formation of La-containing particles and clusters around eutectic Mg2Si phase, which effectively prevents the diffusion of Mg and Si atoms, inhibits the growth of eutectic Mg2Si, and promotes a change in its growth direction. Dry sliding wear tests under different loads applied, with a sliding speed of 0.8 m/s and at a room temperature indicated that the COF and wear rate of all La-added alloys are lower than those of unmodified alloy, with higher hardness and better wear resistance. Among them, 0.4 wt.% La-added alloy has the lowest COF and wear rate, highest hardness, and best wear resistance, which is principally because of the changes in the size, distribution, and morphology of eutectic Mg2Si crystals in the alloy after La modification. Furthermore, severe abrasive and delamination wear are mainly in the unmodified and 0.8 wt.% La-added alloys, while adhesive and abrasive wear characterize in the 0.4 wt.% La-added alloy. In addition, the abrasive wear is dominant under light load, but under heavy load shows delamination and oxidation wear. The 0.4 wt.% La-modified Al-11%Mg2Si hypoeutectic alloy with the improved wear resistance is expected to be applied in automotive components with high wear resistance requirements, such as pistons.
