Evolution of the Microstructure and Mechanical Properties of Al-B Composite with the Ultrafine-Grained Aluminum Matrix

Abstract

The paper examines the microstructural evolution of alloy 1565ch of the Al-Mg-Mn-Zn-Zr system during thermomechanical treatment, including severe plastic deformation by high-pressure torsion or equal channel angular pressing according to the Conform scheme and subsequent isothermal rolling at 200°C. Formation of the nanostructured and ultrafine-grained states in alloy 1565ch with the controlled distribution of the Al₃Mg₂, Al₆Mn and Al₃Zr phases both inside grains and at their boundaries allows for the effect of superplasticity at the temperatures 250 and 300°C and strain rates 5 × 10^–2, 10^–2, and 5 × 10^–3 s^–1. Microstructural analysis by transmission electron microscopy shows that superplastic deformation at the temperatures 250 and 300°C allows a homogeneous ultrafine-grained state to be preserved. The studied ultrafine-grained aluminum alloy 1565ch has a high strength and the ability to relieve stresses, and therefore it can be favorably used as the matrix material in composites reinforced with continuous boron fibers. In the paper, we use this alloy to study special features of production of a multilayer (foil–fiber–foil) metal matrix composite by isothermal pressing under low-temperature superplastic conditions. This method has a positive effect on the mechanical properties of the composite, such as ultimate strength at 200°C, impact strength at room temperature, and fracture toughness at room temperature.