Effect of Alternating Magnetic Field on MIG Brazing of Aluminum-Copper Joints

Literature Overview

This study by Wang Long and colleagues from Nanchang Hangkong University investigates the influence of an alternating intermittent magnetic field on gas metal arc (GMA) brazing of T2 copper plate to 2A16 aluminum alloy plate, using ER5356 aluminum-magnesium wire with a 1.2 mm diameter. The research is funded by the National Natural Science Foundation of China (Grant 51865034) and the Graduate Innovation Fund of Nanchang Hangkong University (YC2019015), and was published in the journal Rare Metals, Volume 46, Issue 12, pages 1657–1662, in 2022. The work addresses a practical and persistent challenge in dissimilar metal joining: the formation of brittle intermetallic compounds (IMCs) at the aluminum-copper interface, which severely compromises joint strength and ductility.

Core Technical Findings

The authors systematically varied the magnetic excitation parameters and evaluated joint performance through macroscopic morphology, microstructural examination, and tensile testing. The most striking result is the dramatic improvement in wetting behavior when the alternating magnetic field is applied. The wetting angle decreases from 113.3° to 57.5°, and the spreading coefficient increases from 93% to 144%, indicating a substantial enhancement in molten metal flow and coverage. This is significant because poor wetting in aluminum-copper brazing is a primary cause of incomplete joint formation and weak bonding.

The microstructural analysis reveals that the types of intermetallic compounds formed at the interface remain unchanged with or without the magnetic field. Both conditions produce AlCu and Al₂Cu phases. However, the morphology of the IMC layer undergoes a fundamental transformation: under the magnetic field, the IMC layer shifts from a flat, planar shape to a wavy configuration. The Al₂Cu layer exhibits non-uniform thickness and growth direction, creating what the authors describe as a "self-locking" effect. This interlocking morphology effectively prevents crack initiation and propagation at the interface, as no interfacial cracks were observed in the magnetic-field-assisted joints.

The tensile strength results demonstrate the practical significance of these microstructural changes. At the optimal parameters—welding current of 100 A, welding speed of 240 mm/min, excitation current of 0.6 A, and excitation frequency of 15 Hz—the joint achieves a maximum tensile strength of 135.47 MPa, representing a 35.88% improvement over the baseline without magnetic field. The trend analysis shows that increasing the excitation current initially raises tensile strength but eventually causes a decline, while increasing the excitation frequency consistently reduces strength. The influence of excitation current on tensile strength is more pronounced than that of excitation frequency.

Process Parameters and Their Interpretation

The interaction between excitation current and frequency warrants careful engineering consideration. The non-monotonic relationship between excitation current and tensile strength suggests an optimal window exists, beyond which excessive magnetic stirring may destabilize the molten pool or promote unfavorable solidification patterns. The monotonic decrease in strength with increasing frequency may be attributed to reduced magnetic flux density at higher oscillation rates, diminishing the stirring effect on the molten pool.

Engineering Practice Implications

For engineers working on dissimilar metal joints in aerospace, automotive, and heat exchanger applications, this study provides a viable pathway to improve aluminum-copper joint integrity without changing base materials or filler metals. The alternating magnetic field technique is non-invasive and can potentially be integrated into existing GMA welding setups with the addition of an electromagnet and power supply. The "self-locking" IMC morphology is particularly valuable because it addresses the fundamental metallurgical challenge of brittle intermetallic formation rather than merely masking it.

However, several practical considerations must be addressed before industrial implementation. The magnetic field generation system adds complexity and cost to the welding setup. The optimal parameters identified in this study are specific to the 1.2 mm ER5356 wire and the particular plate geometry tested; scaling to different thicknesses, joint configurations, or production speeds would require additional parameter optimization. Furthermore, the study does not address fatigue performance, corrosion resistance, or long-term creep behavior of the magnetic-field-assisted joints, all of which are critical for structural applications.

Study Insights and Reflections

The most intellectually stimulating aspect of this research is the morphological transformation of the IMC layer from planar to wavy. This observation connects electromagnetic stirring theory with interfacial metallurgy in a way that is both elegant and practically useful. The wavy IMC interface creates mechanical interlocking that resists crack propagation, analogous to the concept of crack deflection and bridging in fracture mechanics. This insight could potentially be extended to other dissimilar metal systems where IMC formation is unavoidable, such as aluminum-titanium, copper-aluminum, and steel-aluminum joints.

The finding that excitation current has a greater influence on tensile strength than excitation frequency aligns with the principle that magnetic flux density, rather than oscillation rate, is the dominant factor in electromagnetic stirring intensity. This has direct implications for the design of magnetic field-assisted welding systems: the excitation current should be the primary parameter controlled, while frequency serves as a secondary tuning variable.

In summary, this study demonstrates that an alternating intermittent magnetic field can substantially improve the wetting, microstructural integrity, and tensile strength of MIG-brazed aluminum-copper joints through electromagnetic stirring of the molten pool and the creation of a self-locking IMC morphology. The technique offers a promising route to overcoming the inherent brittleness of intermetallic compounds in dissimilar metal joining, though further research on fatigue, corrosion, and scale-up is essential before widespread industrial adoption.