Thermal Equilibrium and Process Stability Analysis of Aluminum Alloy MIG Arc Additive Manufacturing

Literature Overview

This paper, published in Ordnance Materials and Science Engineering (2026, Vol. 49, No. 2, pp. 48-54), investigates the thermal equilibrium and process stability of MIG arc additive manufacturing (AM) of Al-Mg alloys. The research team from Inner Mongolia University of Technology, led by Bao Xulei, combined high-speed camera imaging, electrical signal acquisition, and thermal analysis to understand the droplet transition behavior and its impact on build quality. Supported by multiple funding sources including the National Natural Science Foundation (52265054), this study addresses fundamental process physics that govern the stability of multi-layer AM builds.

Droplet Transition Behavior and Current Effects

The study examines how welding current affects droplet transition frequency and arc heating area, which directly influence the quality of the deposited layers:

When the forming current exceeds 140 A, the droplet transition frequency increases and the arc heating area expands, which is detrimental to achieving a small formation coefficient. The enhanced lateral forces on the molten pool at higher currents lead to pool instability and degraded layer geometry. This finding establishes 140 A as a critical threshold for process stability in Al-Mg alloy MIG AM.

Thermal Analysis and Equivalent Heat Dissipation Power

The study introduces the concept of equivalent heat dissipation power to characterize the thermal balance in multi-layer AM builds. The key findings regarding thermal behavior are:

In the initial cladding stages, good heat dissipation conditions result in gradual changes in equivalent heat dissipation power. As the number of layers increases, the heat dissipation power decreases more sharply, leading to significant heat accumulation. This accumulation makes the liquid pool highly susceptible to instability, which manifests as pool spreading, layer collapse, or geometric inconsistencies.

Process Stability Mechanism

The study reveals a fundamental mechanism governing process stability in MIG AM:

1. Heat input vs. heat dissipation balance: At lower currents (140 A), the heat input is balanced by the heat dissipation capacity of the build, maintaining a stable thermal equilibrium.
2. Progressive degradation: As layers accumulate, the thermal mass increases but the surface-to-volume ratio decreases, reducing the relative heat dissipation capacity.
3. Critical threshold: When heat accumulation exceeds a critical level, the pool becomes unstable, leading to loss of geometric control.

The finding that maintaining constant equivalent heat dissipation power at 140 A yields optimal formation quality suggests that process stability is fundamentally governed by thermal balance rather than by any single process parameter.

Engineering Practice Integration

For engineers developing or optimizing MIG AM processes for aluminum alloys, this study provides several actionable insights:

1. Current selection: 140 A represents the optimal current for Al-Mg alloy MIG AM, balancing deposition rate with process stability.
2. Thermal monitoring: Monitoring equivalent heat dissipation power during the build can serve as an early warning indicator of impending pool instability.
3. Layer strategy: The progressive degradation of thermal balance suggests that build strategies should account for layer position, potentially incorporating cooling pauses or parameter adjustments at critical layer transitions.
4. Quality prediction: The correlation between thermal state and formation quality enables predictive quality assessment during the AM process.

Key Questions and Reflections

A significant question is whether the 140 A threshold identified for Al-Mg alloys applies to other aluminum alloy systems. Different alloys have different thermal conductivities, melting points, and solidification characteristics, all of which affect the thermal balance. Engineers should expect that the optimal current will vary with alloy composition and should develop alloy-specific process windows through similar thermal analysis.

Another reflection concerns the scalability of these findings to larger builds. The study likely uses relatively small specimens, but in industrial AM applications, builds can be much larger and more complex. The thermal dynamics of large builds may differ significantly from those of small specimens, particularly in terms of heat accumulation patterns and the spatial distribution of thermal stresses. Engineers should consider how the principles identified in this study translate to production-scale AM operations.

Study Insights and Implications

The most significant insight from this study is that process stability in MIG AM is fundamentally governed by thermal balance, and that the equivalent heat dissipation power provides a quantitative metric for assessing and controlling this balance. The identification of 140 A as the optimal current for Al-Mg alloy MIG AM, combined with the understanding of progressive thermal degradation during multi-layer builds, provides a solid foundation for process optimization.

For engineers working in additive manufacturing of aluminum alloys, this study demonstrates that process stability cannot be achieved through parameter optimization alone—it requires an understanding of the underlying thermal physics and the ability to monitor and control the thermal state during the build. The concept of equivalent heat dissipation power offers a practical tool for process monitoring and control, and the findings regarding current thresholds provide clear guidance for process development. This work advances the fundamental understanding of MIG AM process physics and provides practical tools for achieving stable, high-quality builds of aluminum alloy components.