CLADDING TECHNOLOGY SHANXI CO., LTDPulsed DE-MIG Brazing of Aluminum and Galvanized Steel Dissimilar Metals
Literature Overview
This research, published in the Materials Science and Technology journal in 2014 by Gu Yufeng and colleagues from Lanzhou University of Technology, investigates the pulsed double-electrode metal inert gas (DE-MIG) brazing method for joining aluminum and galvanized steel dissimilar metals. The work was supported by multiple national science foundation grants and institutional programs, reflecting its significance in the field of dissimilar metal joining. The study addresses one of the most challenging problems in automotive and structural engineering: achieving reliable, corrosion-resistant joints between aluminum alloys and galvanized steel sheets without forming brittle intermetallic compounds (IMCs) that compromise joint integrity.
Core Technical Content
The fundamental challenge in joining aluminum to galvanized steel lies in the metallurgical incompatibility between the two base metals. When direct fusion welding is attempted, iron-aluminum intermetallic phases such as FeAl, Fe₂Al₅, and FeAl₃ form at the interface. These phases are extremely brittle, with fracture toughness values typically below 10 MPa·m^0.5, and can propagate cracks under thermal cycling or mechanical loading. The DE-MIG brazing approach circumvents this problem by maintaining the base metals in a solid state while melting only the filler material, which acts as the bonding agent.
The double-electrode configuration is particularly significant because it allows independent control of heat input on each side of the joint. By positioning one electrode closer to the galvanized steel and the other closer to the aluminum, the operator can manage the asymmetric thermal expansion coefficients of the two metals. Galvanized steel has a thermal expansion coefficient of approximately 12×10⁻⁶/K, while aluminum alloys such as 5052 or 6061 typically exhibit values around 23×10⁻⁶/K. This mismatch creates residual stresses during cooling that can lead to warping or cracking if not properly managed.
| Parameter | Typical Value | Rationale |
|---|---|---|
| Pulse frequency | 50–200 Hz | Controls droplet transition and heat input stability |
| Pulse current | 200–400 A | Melts filler without excessive base metal penetration |
| Background current | 80–150 A | Maintains arc stability between pulses |
| Shielding gas | Ar/CO₂ (80/20) or pure Ar | Minimizes oxidation of aluminum and zinc spatter |
| Filler wire | AlSi5 or AlMg5 | Low melting point enables brazing without base metal fusion |
| Travel speed | 300–600 mm/min | Balances heat input and joint geometry |
| Electrode diameter | 1.0 or 1.2 mm | Standard consumable for DE-MIG configuration |
Process Analysis and Engineering Practice
The pulsed mode of DE-MIG welding provides superior control over the welding process compared to continuous current modes. Each pulse deposits a single droplet of molten filler metal, which cools and solidifies before the next pulse arrives. This cyclic heating and cooling reduces the peak temperature at the joint interface, keeping it below the melting point of both base metals while allowing the filler to flow and wet the surfaces. The zinc coating on the galvanized steel presents additional challenges: zinc has a vapor pressure that becomes significant above 300°C, leading to zinc evaporation that can cause porosity and spatter in the weld.
From an engineering quality control perspective, several inspection methods are relevant. Visual inspection should reveal a uniform bead profile with no excessive spatter or zinc burn-off. Dye penetrant testing (PT) can detect surface cracks in the brazed seam. Ultrasonic testing (UT) at frequencies of 5–10 MHz can evaluate the bond quality between the filler and base metals, though the thin bond line requires careful calibration. Cross-sectional metallographic examination reveals the intermetallic layer thickness, which should ideally remain below 10 μm for adequate ductility.
In automotive body-in-white applications, where this technology finds primary use, the joint strength requirements are governed by standards such as ISO 14632 for spot welds and OEM-specific specifications for continuous joints. The brazed joints typically achieve tensile strengths in the range of 100–180 MPa, which is lower than fusion-welded joints but sufficient for many structural applications where corrosion resistance is prioritized over ultimate strength.
Key Reflections and Study Insights
The most compelling aspect of this research is its practical relevance to the automotive industry's ongoing transition toward lightweight vehicle construction. As automakers seek to reduce vehicle mass through aluminum body panels while retaining galvanized steel for crash-worthy structural members, reliable dissimilar metal joining technologies become critical. The DE-MIG approach offers advantages over resistance spot welding (RSW), which often produces unstable nuggets at aluminum-steel interfaces due to the thermal conductivity mismatch.
One area for further investigation is the long-term durability of these brazed joints under cyclic loading conditions. While static tensile tests demonstrate acceptable performance, fatigue behavior under mixed-mode loading (as encountered in real vehicle structures) remains less well characterized. Additionally, the effect of zinc coating thickness on joint quality warrants systematic study, as thicker coatings may introduce more zinc vapor into the weld zone, potentially degrading bond quality.
The study also highlights the importance of process parameter optimization through systematic experimental design. The interaction between pulse frequency, travel speed, and electrode offset distance creates a complex parameter space where small deviations can lead to significant changes in joint quality. Engineers implementing this technology in production environments should invest in statistical process control (SPC) methods to maintain consistent weld quality across long production runs.
This research contributes meaningfully to the body of knowledge on dissimilar metal joining, and its findings should be considered alongside alternative approaches such as self-piercing riveting (SPR) and flow-drilled fastening (FDF) when selecting the optimal joining method for specific applications. The pulsed DE-MIG brazing technique offers a promising solution for high-volume manufacturing scenarios where continuous joints are required and corrosion resistance is a primary design driver.