3.1. Microstructural of an Al/TiB2 and Al/TiB2/Cu MMCs
Figure 3a depicts the optical microstructures of Al/6wt. % TiB2 MMC. The TiB2 reinforcing particles were clearly distributed uniformly in the aluminium matrix. Furthermore, some regional agglomeration of TiB2 particles was observed at the grain boundaries, as shown in Figure 3a. Because the fine TiB2 particles are pushed away from the interdendritic region by the solidification front during the solidification process. Furthermore, a large number of elongated dendritic grains appear in compounds. As shown in Figure 3b, Microstructure of Al/6wt. % TiB2/4wt.% Cu MMC, TiB2 particles are uniformly distributed in the matrix, and copper particles have a high brightness. The brightness of Cu particles is caused by their higher atomic number when compared to base aluminium [8].
Because of the ductile nature of copper, copper adds toughness to the composite [9]. Auradi et al. (2014) investigated Microstructure and mechanical characterization of AlTiB2 in situ metal matrix compounds produced via master alloy path and discovered the presence of hexagonal TiB2 particles with fairly uniform distribution in the a-Al matrix, as well as traces of Al3Ti particles. Ramesh et al. (2011) investigated the microstructural and mechanical properties of in-situ Al 6061/TiB2 composites. The optical microphotographs of Al 6061 alloy and developed composites show uniformly distributed TiB2 particles as well as traces of flake such as Al3Ti.
The XRD results of the base metal and its compounds are shown in Figure 4.a-c. Shown depicts the base metal results, which show the presence of aluminium and its alloying elements such as Si and mg. As shown in Fig. 4b, XRD results of Al/TiB2 composite results, the presence of TiB2 particles coupled with Al3Ti brittle phase [10] is confirmed. The presence of TiB2 particles, Al3Ti brittle phase, and copper is confirmed by the XRD results of an Al/6wt. % TiB2/4wt. % Cu composite, as shown in Fig. 4c. The presence of copper reduces the formation of clusters and Al3Ti brittle phases compared to the Al/6wt. percent TiB2 XRD result. This phenomenon is crucial in achieving the superior properties of Al/6wt. % TiB2/4wt. % Cu composite over Al/6wt. % TiB2 composite. Because Al3Ti is a naturally brittle phase, the toughness of the composite increases as the amount of Al3Ti intermetallic phases and clusters decreases.
3.2. Mechanical Property of Al/TiB2 and Al/TiB2/Cu MMCs
The mechanical properties of Al/6wt. % TiB2, Al/6wt.% TiB2/4wt.% Cu MMC, and its base metal are shown in Table 2 and Fig. 5. TiB2 particle has smaller grain formed both MMCs in permanent mould condition. Base metal properties such as UTS, hardness, and fracture toughness are 95 MPa, 70 BHN, and 9.6 Mpa\(\sqrt{m}\), respectively, whereas the corresponding properties for Al/6wt. percent TiB2 composite are 124 MPa, 93 BHN, and 19.33 Mpa. UTS, hardness, and fracture toughness of Al/6wt. % TiB2 composite over base metal are improved by 30.52 percent, 32.85 percent, and 101.35 percent, respectively. Mechanical properties are generally determined by the nature and properties of matrix and reinforcement materials .The compatibility of matrix and reinforcement also plays an important role in improving the UTS of composites. The reinforcement particles act as a barrier against dislocation movements under load. As a result, more loads are required for void nucleation and propagation, resulting in higher tensile strength in composites. The presence of TiB2 particles in the composites improved the mechanical properties of the composites. UTS, hardness, and fracture toughness of Al/6wt. percent TiB2/4wt. percent Cu composites are 158 MPa, 114 BHN, and 23.19 Mpa\(\sqrt{m}\), respectively. The UTS, hardness, and fracture toughness improvements of Al/6wt. % TiB2 composite over base metal are 66.31 percent, 62.85 percent, and 141.56 percent, respectively.
This is due to the presence of TiB2 particles in the aluminium matrix, which results in an increase in mechanical properties. The presence of Cu has a significant impact on the final properties of the Al/6wt. % TiB2/4wt. % Cu composite. Because of the ductility and toughness of Cu, it has higher fracture toughness. [11–12]. the grain refinement and fineness of the reinforcement are also important factors in determining the hardness of composite materials. The addition of copper reduces the formation of clusters and Al3Ti brittle phases, so copper acts as a grain refiner for the Al/6wt. % TiB2/4wt. % Cu composite. Furthermore, during in-situ composite fabrication, an exothermic reaction occurs, resulting in fine and clear interfacial bond. Due to the manufacturing technology and the strength of the casting, the hardness of the composite material is significantly improved and the load transfer capacity of the matrix to the reinforcement is enhanced by the reaction free interface.