Characteristics and properties of Mg/Al bimetallic solid-phase composite interfaces

Abstract

Mg/Al bimetallic layered composites are in great demand for lightweight and high-performance manufacturing applications owing to the advantageous combination of the low density of magnesium alloys and the corrosion resistance of aluminum alloys. The bimetallic solid-phase composite fabrication process, in which the contact surfaces of metal materials are directly combined in the solid state, offers significant advantages in bimetallic composite technology. This process avoids the detrimental effects of oxidation, inclusions, and other defects that can impact the performance of composite materials formed through liquid–liquid or liquid–solid composite processes. Temperature, strain rate, and strain are critical parameters in many joining and forming processes of Al/Mg alloy hybrid structures/components, but the relationship between these parameters and interfacial bonding strength remains to be quantified. In this study, hot compression composite experiments were conducted to elucidate the influence of heat deformation conditions on the performance of the Mg/Al bimetallic composite interface. The experiments were performed at deformation temperatures of 300–430 ℃, strain rates of 5×10−3–1 s−1, and strains of 20%–40%. A scanning electron microscope with energy dispersive spectroscopy (SEM–EDS) and a Vickers hardness tester were used to analyze the microstructure, element distribution, and hardness distribution of the composite interface. The results showed that the bonding interface was not effectively formed owing to the presence of micro-gaps at a strain of 0.2 or a temperature of 300 ℃. Furthermore, the strain rate mainly affected the shape of the bonding interface, indicating that strain and temperature were the critical factors influencing metallurgical bonding in the bimetallic compounding process. As the strain rate decreased and deformation and temperature increased, the element diffusion time increased, and diffusion ability improved. This resulted in a thicker transition region and the formation of high-hardness intermetallic compounds (IMCs) composed of Mg17Al12 and Al3Mg2 phases. According to this, an evolution model of the intermetallic compound layer thickness in the transition region, parameterized by the elemental diffusion activation energy, was established. Through the incorporation of the critical strain required for the bimetal to achieve metallurgical bonding, a diagram illustrating the evolution of the Mg/Al bimetallic composite interface under various heat deformation conditions was constructed. Metallurgical bonding was achieved through the complete diffusion of metal atoms at the interface; however, the hardness and brittleness of the resulting intermetallic compound layer were not conducive to the quality of the Mg/Al bimetallic interface. Therefore, considering metallurgical bonding and the characteristics of the intermetallic compound layer is essential. Controlling the extent of elemental diffusion allowed for minimizing the thickness of the intermetallic compound layer while ensuring effective interfacial metallurgical bonding. The calculation results indicated that deformation conditions of higher temperature (>400 ℃) and higher strain rate (～1 s−1) could inhibit the formation and growth of the intermetallic compound layer while ensuring metallurgical bonding, thus contributing to a high-quality composite interface. The combination of high strain rates and high temperatures enabled the formation of a fully bonded interface with a minimal intermetallic compound layer thickness, maximizing bonding strength. The research findings and developed models can guide the optimization of parameters associated with the Mg/Al bimetallic joining or forming process via plastic deformation.

Keywords

• mg/al bimetallic
• composite interface
• element diffusion
• microstructure
• thickness evolution model