Microstructural characteristics and mechanical behavior of in-situ synthesized AA2024– AlB2 composites produced via friction stir processing

The in-situ AA2024–AlB₂ composites processed via friction stir processing reveal a strong dependency of both microstructural evolution and mechanical performance on processing parameters. When the tool rotates at 800 rpm, the process yields a fine-grained structure averaging around 2.8 μm, while also ensuring effective stabilization and uniform distribution of AlB₂ reinforcements. These conditions lead to a notable improvement in material properties, with hardness reaching 134.2 HV0.1 and tensile strength climbing to 508.2 MPa—an enhancement of 11.8 % over the unprocessed alloy (454.3 MPa). At this speed, the peak temperature remains controlled at approximately 467 °C, minimizing defects such as tunnel voids. In contrast, increasing the rotational speed to 1200 rpm generates excessive heat (above 495 °C), which accelerates grain coarsening (average grain size increases to 5.8 μm) and promotes particle clustering. These microstructural deteriorations correspond with a drop in hardness (106.6 HV_0.1) and mechanical strength. Therefore, the study identifies 800 rpm as the optimal processing speed, offering the best compromise between thermal input and strain rate to maximize material performance and microstructural uniformity.