• Adding 0.2 wt.% La to cast Al-Mg-Si alloy simultaneously improves tensile strength and electrical conductivity, achieving UTS of 170 MPa and conductivity of 44.0% IACS.
• La addition refines α-Al grains, promotes Mg2Si precipitation, and transforms AlFeSi phase from continuous to discontinuous, enhancing mechanical and electrical properties.
• The improvements over La-free alloy are significant: UTS +9.0%, YS +15.8%, elongation +70.3%, and conductivity +17.3%.
• Excessive La content deteriorates properties, indicating an optimal La concentration for balanced performance.