Effects of the addition of lanthanum and ultrasonic stirring on the microstructure and mechanical properties of the in situ Mg2Si/Al composites

Highlights: • La addition to Mg₂Si/Al composite led to decreased particle size of Mg₂Si phase. • La addition to Mg₂Si/Al composite led to increased globularity of Mg₂Si particles. • Ultrasonic stirring combined with La addition led to enhanced strength. • Ultrasonic stirring combined with La addition led to improved elongation. In this study, an in situ Mg₂Si/Al composite was fabricated with the addition of lanthanum (La) combined with ultrasonic stirring at different powers during solidification. The composite exhibited simultaneously enhanced tensile strength and elongation because of the positive effects of La addition and ultrasonic stirring on microstructure. X-ray diffraction analysis, optical microscopy and scanning electron microscopy were used for the microstructural characterization. Hardness and tensile tests were used for the evaluation of the mechanical properties. The results indicated that the Mg₂Si/Al composite with the addition of 0.4 wt.% La combined with ultrasonic stirring at a power of 150 W exhibited a unique combination of mechanical properties including a hardness of 132 HB, a tensile strength of 201 MPa, and an elongation of 5.28%; while the composite without La addition nor ultrasonic stirring exhibited a hardness 76 HB, a tensile strength 84 MPa and an elongation 2.02%. This study demonstrated that a minor La addition combined with 150 W ultrasonic stirring is a promising approach in modifying the microstructure and enhancing the mechanical properties of the in situ Mg₂Si/Al composite for industrial applications.