Microstructure and mechanical characterization of in situ synthesized AA6061/(TiB2+Al2O3) hybrid aluminum matrix composites

TiB2 and Al2O3 particulates reinforced AA6061 aluminum matrix composites (AMCs) were synthesized by in-situ reaction of titanium (Ti) and boric acid (H3BO3) powders with molten aluminum. AMCs were fabricated using an electric stir casting furnace under a controlled environment. Heat flow curves of differential thermal analysis (DTA) showed that the synthesis temperature for the formation of TiB2 and Al2O3 using Al-Ti-H3BO3 reaction system was 950 °C. The in-situ synthesized composites were characterized using XRD, FESEM, TEM and EBSD. XRD results revealed the formation of TiB2 and Al2O3 particulates in the composite. FESEM micrographs revealed a homogenous distribution of both the particulates with good interfacial bonding. EBSD maps showed that the in-situ formed TiB2 and Al2O3 particulates refined the grains of the aluminum matrix from 103 μm at 0 wt% to 14 μm at 15 wt%. Al2O3 particles exhibited spherical shape while TiB2 particles displayed hexagonal and cubic shapes. The formation of ultrafine and nano scale thermodynamically stable TiB2 and Al2O3 particles enhanced the microhardness and the tensile strength of the AMCs. The microhardness and the tensile strength were respectively 122 HV and 287 MPa at 15 wt%. [Display omitted] •Synthesis of AA6061/(TiB2 + Al2O3) AMCs by in situ reaction of Ti and H3BO3.•The synthesis temperature for the formation of TiB2 and Al2O3 is 950 °C.•TiB2 and Al2O3 particulates refined the grains of the aluminum matrix.•TiB2 and Al2O3 particulates were characterized with hexagonal and spherical shape.•Most of the particulates were sub-micron and nano scale.