Aluminum and magnesium alloys, with their excellent properties such as low density, high specific strength, and corrosion resistance, are widely used in aerospace, automotive manufacturing, and rail transportation. However, these two lightweight metal alloys are highly chemically reactive, easily forming oxide films and brittle intermetallic compounds during welding, resulting in poor joint mechanical properties and limiting their further application in high-end equipment manufacturing. Ultrasonic brazing technology, by introducing ultrasonic vibration to assist the spread of the brazing filler metal and the interfacial reaction, effectively solves the technical bottleneck of aluminum-magnesium alloy joining, significantly improving the joint's strength, toughness, and other core mechanical properties.
The core mechanism by which ultrasonic brazing improves the performance of aluminum-magnesium alloy joints is reflected in three aspects. First, the cavitation effect generated by ultrasonic vibration can instantly destroy the oxide film on the surface of aluminum and magnesium alloys. The oxide film on the surface of aluminum-magnesium alloys is dense and has a high melting point, making it difficult to remove with conventional brazing. However, the microjets and shock waves formed by ultrasonic cavitation can break and disperse the oxide film, allowing the brazing filler metal to directly contact the base metal, laying the foundation for forming a strong joint. Second, ultrasonic vibration accelerates the interfacial diffusion between the brazing filler metal and the base metal. Under the influence of ultrasonic energy, the diffusion coefficient between brazing filler metal atoms and aluminum and magnesium atoms is significantly increased, promoting interfacial metallurgical bonding and reducing defects such as interfacial porosity. Thirdly, ultrasonic vibration can refine the grain size of interfacial intermetallic compounds. During brazing of aluminum-magnesium alloys, brittle Al-Mg series intermetallic compounds easily form; excessive growth severely reduces joint toughness. Ultrasonic vibration can inhibit excessive compound growth, refine grain size, and improve the overall mechanical properties of the joint.
The selection of brazing filler metal is a crucial step in ultrasonic brazing of aluminum-magnesium alloys. An ideal brazing filler metal needs good wettability, a moderate melting point, and chemical compatibility with the aluminum-magnesium alloy. Currently, commonly used brazing filler metals mainly include aluminum-based, zinc-based, and rare-earth modified filler metals. Aluminum-based filler metals have good compatibility with the aluminum alloy matrix and can form joints with high strength; zinc-based filler metals have a low melting point and excellent fluidity, making them suitable for magnesium alloy components that are sensitive to welding temperature; rare-earth modified filler metals optimize the spreadability of the filler metal by adding rare earth elements, further improving the interfacial bonding state and enhancing the mechanical properties of the joint. In practical applications, the composition and specifications of the brazing filler metal must be rationally selected based on the specific grade and service requirements of the aluminum-magnesium alloy.
Ultrasonic parameters also have a significant impact on the performance of aluminum-magnesium alloy brazed joints. The matching degree of parameters such as ultrasonic power, welding time, and welding temperature directly determines the oxide film removal effect, the degree of interfacial diffusion, and the growth state of intermetallic compounds. Too low a power will not completely break down the oxide film, while too high a power may cause overheating damage to the joint; too short a welding time will result in insufficient interfacial bonding, while too long a time may lead to excessive growth of brittle compounds. Therefore, it is necessary to optimize the parameter combination through experiments to maximize the mechanical properties of the joint.
With the increasing demand for lightweight metal alloys in high-end manufacturing, ultrasonic brazing technology, with its unique technical advantages, has an increasingly broad application prospect in aluminum-magnesium alloy joining.
In the future, through in-depth research on brazing filler metal composition optimization, ultrasonic action mechanisms, and intelligent control of process parameters, it is expected to further improve the mechanical properties and reliability of aluminum-magnesium alloy brazed joints, promoting their application in more demanding service environments.
