Microstructural evolution and enhancement of mechanical and corrosion properties of La 2 O 3 /B 4 C reinforced Al7075 hybrid composites

This study investigates the effect of lanthanum oxide (La 2 O 3 ) and boron carbide (B 4 C) reinforcements on the microstructure, mechanical properties, and hydrophobic behavior of Al7075 hybrid composites fabricated via the stir-casting technique. The B 4 C was varied from 1.5 to 3.5 wt.%, while the La 2 O 3 ranged from 0.5 to 1.5 wt.%. The microstructural evolution and phase constitution were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD), which confirmed the successful incorporation and relatively uniform distribution of the reinforcements within the Al7075 matrix. The addition of La 2 O 3 and B 4 C significantly enhanced the mechanical performance of the composites. The hybrid composites exhibited hardness improvements of 18.17%, 31.48%, 59.55%, 66.05%, 31.55%, 26.53%, 27.56%, 12.16%, and 23.18%, respectively, compared with the unreinforced Al7075 alloy. A maximum Vickers hardness of 168.74 HV was achieved corresponding to 1 wt.% La 2 O 3 and 1.5 wt.% B 4 C reinforcements. The highest impact strength of 14.0 J, representing a 97.18% improvement compared with the Al7075 alloy, was obtained for the composite reinforced with 1.5 wt.% La 2 O 3 and 2.5 wt.% B 4 C. The maximum contact angle of 103.1° was obtained for the hybrid composite reinforced with 1.5 wt.% La 2 O 3 and 2.5 wt.% B4C. The remaining hybrid composites also exhibited average contact angles exceeding 90°, confirming their hydrophobic surface characteristics. The enhanced hydrophobicity can be attributed to the combined effects of La 2 O 3 and B 4 C reinforcement on the surface morphology of the Al7075 matrix. The corrosion resistance of the hybrid composites was significantly enhanced, with reductions in corrosion rate (CR) of 74.1%, 63.0%, 86.1%, 45.4%, 45.9%, 75.3%, 23.4%, 84.1%, and 49.5% for samples S1–S9, respectively, compared with the unreinforced Al7075 alloy. The results demonstrate controlled fabrication. The findings confirm that La 2 O 3 and B 4 C effectively enhance the surface and mechanical properties of Al7075 hybrid composites for advanced engineering applications.