CLADDING TECHNOLOGY SHANXI CO., LTDMIG Welding Process Research on Dissimilar Aluminum Alloy Joints
Literature Overview
This 2021 study from FAW-Volkswagen Co., Ltd., authored by Zhang Zhiyun and Tong Wei, published in Precision Forming Engineering, investigates the MIG welding process for dissimilar aluminum alloy joints. The automotive industry context provides strong motivation for this research, as lightweight vehicle structures increasingly employ dissimilar aluminum alloy combinations to optimize strength-to-weight ratios, corrosion resistance, and formability simultaneously.
Core Technical Content
Dissimilar aluminum alloy welding presents unique challenges compared to homogenous alloy welding. When joining two different aluminum alloys, the molten pool composition becomes a function of dilution rates, which are governed by the relative thermal conductivities, melting points, and thermal expansion coefficients of the base metals. The resulting weld metal properties may fall outside the acceptable range for either base material unless carefully controlled.
Dissimilar Alloy Combinations and Their Challenges
| Alloy Combination | Primary Challenge | Recommended Filler |
|---|---|---|
| 5052/6061 | Dilution asymmetry, differential thermal expansion | ER5356 or ER4043 |
| 5083/6061 | Silicon enrichment on 6061 side | ER4043 |
| 2024/5083 | High dilution of Al-Cu, cracking sensitivity | ER4043 or ER5183 |
| 6061/7075 | Strength mismatch, T6 temper disruption | ER4043 or ER5183 |
| 5052/7075 | Large thermal conductivity difference | ER4043 with reduced heat input |
Process Parameters for Dissimilar Alloy MIG Welding
The research establishes optimized MIG welding parameters for typical automotive-grade aluminum alloy combinations:
| Parameter | 5052/6061 Joint | 5083/6061 Joint | 6061/7075 Joint |
|---|---|---|---|
| Current (A) | 180–220 | 160–200 | 140–180 |
| Voltage (V) | 19–22 | 18–21 | 17–20 |
| Travel speed (mm/min) | 350–450 | 350–450 | 300–400 |
| Gas flow (L/min) | 15–20 | 15–20 | 15–20 |
| Shielding gas | Ar/He (95/5) | Ar/He (95/5) | Pure Ar |
| Wire diameter (mm) | 1.2 | 1.2 | 1.0 |
| Wire feed speed (m/min) | 4.5–5.5 | 4.0–5.0 | 3.5–4.5 |
Heat Input Asymmetry and Dilution Control
A critical finding in this research is the systematic asymmetry in heat input distribution across dissimilar joints. When welding 5052 (higher thermal conductivity) to 6061 (lower thermal conductivity), the 5052 side absorbs more heat, resulting in greater dilution on that side. The study quantifies this effect:
- For 5052/6061 joints: 55–65% dilution on the 5052 side, 35–45% on the 6061 side.
- For 5083/6061 joints: 52–60% dilution on the 5083 side, 40–48% on the 6061 side.
- For 6061/7075 joints: 45–55% dilution on the 6061 side, 45–55% on the 7075 side (more balanced due to similar thermal properties).
Filler Metal Selection Strategy
The research emphasizes that filler metal selection for dissimilar aluminum alloy joints requires consideration of:
- Solidification cracking resistance: Silicon-containing fillers (ER4043) are preferred for joints involving 6xxx and 7xxx series alloys due to their wide solidification range and reduced hot cracking susceptibility.
- Post-weld strength retention: Magnesium-containing fillers (ER5356, ER5183) provide better strength in the as-welded condition but may promote hot cracking in some combinations.
- Corrosion compatibility: The filler metal should not create galvanic couples with either base metal that would accelerate localized corrosion.
- Thermal expansion matching: The filler should have a coefficient of thermal expansion intermediate between the two base metals to minimize residual stresses.
Engineering Practice Applications
For bimetallic pressure vessel fabrication involving aluminum alloy components—such as aluminum-lined cryogenic vessels or aluminum alloy heat exchanger tubes welded to steel headers—this research provides valuable guidance on managing dissimilar metal weld interfaces. The principles of dilution control, filler selection, and parameter optimization translate directly to overlay welding applications where aluminum alloys are deposited onto dissimilar substrates.
FMEA Analysis of Dissimilar Aluminum Alloy Welding
| Failure Mode | Severity | Occurrence | Detection | RPN | Mitigation |
|---|---|---|---|---|---|
| Hot cracking | 9 | 6 | 3 | 162 | Use ER4043, reduce heat input |
| Cold cracking | 7 | 3 | 4 | 84 | Preheat, low-hydrogen wire |
| Excessive dilution | 8 | 5 | 3 | 120 | Optimize heat input asymmetry |
| Porosity | 6 | 4 | 2 | 48 | Improve gas coverage, clean surfaces |
| Strength loss | 8 | 4 | 3 | 96 | Select appropriate filler, post-weld treatment |
Study Insights and Reflections
The automotive industry's demands for lightweight, high-performance structures drive continuous innovation in aluminum alloy welding technology. This research exemplifies the practical approach needed to address real-world manufacturing challenges. The systematic investigation of parameter effects on dissimilar joints, combined with metallurgical characterization and mechanical testing, provides a comprehensive framework that can be adapted to pressure vessel and cladding applications.
A particularly valuable insight is the recognition that dissimilar aluminum alloy welding requires not just parameter optimization but also strategic planning of the weld sequence and joint geometry. In multi-pass welds or complex joint configurations, the order of welding and the direction of heat input relative to the dissimilar interface significantly affect the final weld quality. Engineers should adopt this systematic approach when designing welding procedures for any dissimilar metal application, whether in automotive, aerospace, or pressure vessel industries.