Aging kinetic and precipitation evolution of Al3BC/2024 Al composites during aging heat treatment

Abstract

In this work, Al₃BC/2024 Al composite has been in-situ fabricated by a liquid-solid reaction method and the influence of Al₃BC particles on the aging kinetics of the composite has been investigated. It is revealed that both the composite and 2024 Al alloys reach a peak hardness at 12 h, indicating a relatively minor impact of Al₃BC on the precipitation process before peak-aging. However, once the over-aging begins, the over-aging process of the composite will be significantly accelerated. The microstructure evolution of the Al₃BC/2024 Al composite during aging process has been then revealed. For the peak-aging composite, the nano S'' precipitates which are seldomly affected by the Al₃BC still distribute homogenously inside the Al grains. However, with the introduction of Al₃BC particles, large amount of defects including Al₃BC/Al interfaces, dislocations and grain boundaries have been introduced into the composite. All these defects lead to an element segregation of Cu and Mg, and thereby promoting the formation of the PFZs and accelerating the nucleation of the S phase. These S precipitates will be coarsed rapidly, thereby accelerating the over-aging of the composite. Finally, through the optimization of the aging process, the tensile strength and elongation of the Al₃BC/2024 Al composite reach up to 659.8 MPa and 3.2%, respectively. The ultrahigh strength of the composite can be attributed to the synergistic strengthening effects of Al₃BC and S'' precipitates.