Development and characterization of LaB₆ reinforced Al-5 wt.% Si hybrid powders and composites prepared by mechanical alloying and pressureless sintering

This study reports the effect of LaB₆ particles on the Al-5 wt.% Si matrix powders and composites in regard of physical, microstructural and mechanical properties. Two different types of LaB₆ particles such as laboratorysynthesized (LaB₆(S)) and commercial (LaB₆(C)) were used as reinforcement materials. (LaB₆(S)) were prepared by mechanochemical synthesis (for 5 h) and leaching (4 M HCl) of La₂O₃-B₂O₃-Mg powder blends. In order to obtain hybrid powders, Al-5 wt.% Si-2 wt.% LaB₆(S) and Al-5 wt.% Si-2 wt.% LaB₆(C) blends were mechanically alloyed (MA'd) for 1, 4 and 8 h in a high-energy ball mill. A hydraulic press with a uniaxial pressure of 450 MPa was used for the compaction of the as-blended/MA'd powders. Green compacts were sintered at 570 °C for 2 h under Ar gas. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) techniques were utilized for the phase and microstructural characterization of the as-blended/MA'd powders and sintered composites. Particle size analysis (PSA) and differential scanning calorimetry (DSC) technique were also conducted on the powder products. Sintered samples were characterized by density and Vickers microhardness measurements and sliding wear tests. With applying MA, physical and mechanical improvements in composite properties were observed. Al-5 wt.% Si-2 wt.% LaB6(C) MA'd for 8 h had the highest density value of 98.11%. Al-5 wt.% Si-2 wt.% LaB6(S) MA'd for 4 h had the highest microhardness value of 115.25±10.12 MPa. Al-5 wt.% Si-2 wt.% LaB6(C) MA'd for 4 h has lower wear volume loss value (0.441) than that of Al-5 wt.% Si-2 wt.% LaB₆(S).