Vol.:(0123456789) 1 3 Arabian Journal for Science and Engineering https://doi.org/10.1007/s13369-019-04256-0 RESEARCH ARTICLE - MECHANICAL ENGINEERING Development of AA2024/TiB 2 + Y 2 O 3 Hybrid Composites with Improved Mechanical Properties Through Stir Rheocasting Semegn Cheneke 1  · D. Benny Karunakar 1 Received: 26 July 2019 / Accepted: 15 November 2019 © King Fahd University of Petroleum & Minerals 2019 Abstract Semisolid cast AA2024 matrix composites reinforced with 2.0 wt% titanium boride (TiB 2 ) and varying amounts of yttria (Y 2 O 3 ) (0.5 wt%, 1.0 wt%, 1.5 wt%) were developed using stir rheocasting. The metallurgical characterisation was done by X-ray difraction, optical microscopy, and scanning electron microscope, and mechanical characterisation by Vickers’s hardness testing machine and universal testing machine. The microstructure evolution and mechanical properties such as hardness, tensile strength, and fracture toughness (K Q ) of the developed composites were correlated. Pure AA2024 and AA2024 reinforced with TiB 2 samples were also fabricated as a benchmark to compare the efect of yttria. The highest hardness, ultimate tensile strength, and yield strength achieved were 122 HV, 310 MPa, and 230 MPa, respectively, for the AA2024/2 wt% TiB 2 + 1.5 wt% Y 2 O 3 composite. They are 25%, 45%, and 57% higher compared to the unreinforced sam- ple. The maximum conditional fracture toughness (K Q ) achieved was 25.56 MPa m 1/2 for the unreinforced specimen and 19.77 MPa m 1/2 for AA2024/2 wt% TiB 2 + 1.5 wt% Y 2 O 3 composite. With the addition of Y 2 O 3 particles in the matrix, the porosity in the samples increased, resulting in lower elongation. The processing route enhanced the mechanical properties of the composite in comparison with the liquid cast matrix due to a uniform distribution of particles and grain refnement. Keywords AA2024 · Microstructure · Mechanical properties · Rheocasting · Hybrid composite · Fracture toughness 1 Introduction Several research activities have been carried out to develop aluminium composite materials with enhanced properties. However, there still appears a need for advanced materials with enhanced mechanical properties. To attain this, alu- minium as a matrix has been reinforced by dispersing small amounts of ceramic particles such as Al 2 O 3 [1, 2], SiC [3–5], and TiB 2 [6–9], which lead to the enhancement of mechani- cal properties such as tensile strength, elastic modulus, wear resistance, and hardness [10]. These composites are used extensively in automobile parts such as connecting rods, cyl- inder liners, and driveshaft, as well as aerospace applications where weight reduction is a critical requirement [11]. Over the years, researchers used TiB 2 particles as rein- forcement due to its outstanding properties such as high hardness, high elastic modulus, high melting point, and good thermal stability, which can improve the performance of the composite [3, 6–9, 12]. Hybrid composites are composites that are developed by dispersion of more than two reinforcements in a matrix. They attracted the attention of researchers due to their out- standing properties derived from the combination of con- stituent reinforcements. They can be potentially used in the automotive, aerospace, energy-saving application, medical, sports, and recreation areas [13–15]. The properties of the hybrid composites mainly depend on the reinforcement materials’ type, shape, size, amount, and uniform distribution [3, 6, 7, 11, 12]. Hadian et al. [6] investigated the microstructure and mechanical properties of Al/(TiC + TiB 2 ) hybrid composite with reinforcement con- tents of 10, 20, 30, and 40 vol%. The specimens were devel- oped using mechanical alloying followed by spark plasma sintering method under 50 MPa pressures, 645 °C sintering temperature, and 15 min holding time. They reported that the Young’s modulus has increased from 73 GPa for the unreinforced alloy to 106 GPa for Al/20 vol% (TiC + TiB 2 ). Similarly, yield strength increased from 105 MPa for the unreinforced alloy to 116 MPa for Al/20 vol% TiC + TiB 2 , * D. Benny Karunakar bennyfme@iitr.ac.in 1 Mechanical and Industrial Engineering Department, Indian Institute of Technology Roorkee, Roorkee 247667, India