Dual-Pulse MIG Brazing of Aluminum-Steel Joints Arc Interaction Effects

Research Background and Motivation

This 2016 paper by Wu Jianfei et al., published in the Transactions of the China Welding Institution (Vol. 37, No. 3, pp. 22-27), addresses a critical challenge in lightweight vehicle manufacturing: the reliable joining of dissimilar aluminum and steel materials. The authors conducted dual-pulse MIG melt-brazing experiments on 6061 aluminum alloy and 304 stainless steel lap joints, using high-speed摄像 and synchronized electrical signal acquisition to capture arc morphology and welding electrical characteristics. The study was supported by the National Natural Science Foundation of China (Grant 51175374) and multiple institutional research programs, reflecting the high priority placed on dissimilar metal joining in the automotive and transportation sectors.

Core Findings on Arc Interaction Mode

The research introduces the concept of arc interaction mode, defined by the combination of torch forward tilt angle and lateral tilt angle, which determines where the arc impinges on the workpiece relative to the lap joint interface. Two configurations were studied:

The wire end distance from the aluminum-steel lap interface (denoted L) was varied at -1, 0, and 1 mm for each mode. The results revealed that Mode A produces welds highly sensitive to arc position changes, meaning small variations in torch positioning lead to significant changes in bead geometry and intermetallic compound (IMC) layer thickness. Mode B, with a 20° lateral tilt, demonstrates robustness to arc position variation, making it more suitable for automated production where precise torch tracking is challenging.

Mechanism of Arc Position Influence

The critical variable identified is the arc interaction position, which governs heat distribution across the dissimilar joint. When the arc impinges predominantly on the aluminum side, excessive heat input can lead to excessive melting of the aluminum substrate, promoting thick IMC layers at the interface. These intermetallic compounds, typically Al-Fe and Al-Cu phases, are brittle and significantly reduce joint strength. Conversely, when the arc is positioned too far toward the steel side, insufficient aluminum melting results in poor wetting and incomplete joint formation.

For Mode A (0° lateral tilt), optimal shear strength was achieved at L = -1, 0, and 1 mm, indicating a relatively wide process window when the arc is symmetrically positioned. For Mode B (20° lateral tilt), the optimal range narrowed to L = 0 and 1 mm, suggesting that the lateral tilt shifts the effective arc interaction zone and requires more precise wire positioning.

Engineering Practice Implications

In automotive body-in-white production, where aluminum and steel are increasingly used in mixed-structure vehicles, the dual-pulse MIG brazing process offers a viable alternative to adhesive bonding and riveting. The finding that lateral tilt angle can decouple arc position sensitivity from weld quality is practically significant: it suggests that process designers can use torch geometry to create a more forgiving process window, reducing the need for expensive high-precision robot positioning systems. However, the trade-off is that Mode B requires careful calibration of the lateral tilt angle to ensure adequate arc coverage of both substrates.

Study Reflection

This work demonstrates that arc interaction mode is not merely a geometric parameter but a fundamental control variable in dissimilar metal welding. The ability to manipulate heat distribution through torch tilt angle represents a powerful tool for process engineers seeking to balance weld quality with production robustness. The dual-pulse mode itself provides additional flexibility through independent control of pulse current and base current, enabling fine-tuning of the heat cycle without altering mechanical parameters.