CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of SLM-AlSi10Mg and 6061-T6 Dissimilar Aluminum Alloy TIG Weld Joints
Literature Overview
This 2026 study published in the Transactions of the Welding Journal investigates the microstructure and mechanical properties of dissimilar TIG weld joints joining selective laser melting (SLM)-fabricated AlSi10Mg alloy to conventionally wrought 6061-T6 aluminum alloy. The research team from the Jin Cheng Nanjing Electromechanical and Hydraulic Engineering Research Center of AVIC and Nanchang Hangkong University, supported by the National Natural Science Foundation of China (Grant No. 52461021) and the Jiangxi Ganpo Juncai Support Plan, addresses an increasingly important manufacturing challenge: the integration of additively manufactured components with conventionally fabricated structural parts. This hybrid manufacturing approach enables the use of SLM for complex geometric features while leveraging conventional forming for large structural elements, but the resulting dissimilar joints present unique metallurgical and mechanical challenges.
Core Technical Points and Microstructural Analysis
Microstructural Characteristics of the Dissimilar Joint
The SLM-AlSi10Mg side of the joint exhibits a distinctive microstructure inherited from the rapid solidification during laser melting, characterized by fine equiaxed grains (2–5 µm), cellular dendrites, and dispersed Si-rich phases (Al5Si) that are much finer and more uniformly distributed than in conventionally cast AlSi10Mg. The 6061-T6 side shows the typical temper-hardened microstructure with fine Mg2Si precipitates responsible for the T6 temper strength. The weld fusion zone and heat-affected zones on both sides develop markedly different microstructures due to the large differences in thermal conductivity, melting range, and solidification behavior between the two alloys.
| Zone | Microstructure | Grain Size | Hardness (HV) |
|---|---|---|---|
| SLM-AlSi10Mg base metal | Fine equiaxed + cellular dendrites | 2–5 µm | ~95 |
| SLM-AlSi10Mg HAZ | Partially melted cellular structure | 3–8 µm | ~85–90 |
| Weld fusion zone | Mixed dendritic structure, Si-rich phases | 8–15 µm | ~75–80 |
| 6061-T6 base metal | Tempered precipitate-hardened | 20–40 µm | ~120 |
| 6061-T6 HAZ | Softened zone, dissolved Mg2Si | 30–50 µm | ~70–80 |
| 6061-T6 TWPZ | Recrystallized, precipitate-free | 15–30 µm | ~65–70 |
Mechanical Property Analysis
The tensile strength of the dissimilar joint was found to be governed by the weakest link, which in this case is the 6061-T6 HAZ where temper softening occurs due to the dissolution of strengthening Mg2Si precipitates. The joint efficiency (ratio of joint tensile strength to the lower base metal strength) was calculated to be approximately 60–70%, which is within the acceptable range for structural aluminum welding but represents a significant reduction from the base metal properties. Fracture analysis confirmed that failure consistently initiated in the 6061-T6 HAZ, indicating that this zone is the critical weak link.
The SLM-AlSi10Mg side, despite its fine microstructure, contributed relatively less to the overall joint strength due to its inherently lower yield strength compared to 6061-T6. However, the fine Si dispersoids in the SLM material provided good resistance to hot short cracking during welding, as confirmed by the absence of solidification cracking in the fusion zone.
Engineering Practice and Process Optimization
Welding Parameter Optimization
The study highlights that welding parameters must be carefully balanced for this dissimilar joint. Excessive heat input causes severe softening of the 6061-T6 side and excessive dilution of the SLM-AlSi10Mg side into the fusion zone, while insufficient heat input leads to incomplete fusion and lack of penetration. The optimal parameters identified were:
| Parameter | Optimal Range | Effect on Joint Quality |
|---|---|---|
| Current (A) | 130–160 | Controls penetration and dilution ratio |
| Travel speed (mm/s) | 3.5–5.0 | Balances heat input and bead geometry |
| Shielding gas flow (L/min) | 12–18 | Prevents oxidation of both alloys |
| Interpass temperature (°C) | <150 | Minimizes HAZ softening on 6061-T6 side |
| Fill wire | ER4043 or ER4047 | Compatible with both base metals |
Dilution Control and Joint Design
The dilution ratio between the two base metals into the fusion zone is a critical factor. A dilution ratio of approximately 45–55% from each side was found to produce the most balanced mechanical properties. Joint design strategies to control dilution include using a backing strip on one side, applying a pre-weld overlay layer of compatible filler metal, or employing asymmetric joint preparation (such as a J-groove with deeper preparation on the 6061-T6 side to reduce dilution from that alloy).
Key Questions and Reflections
A fundamental question in this research is whether the SLM microstructure of AlSi10Mg can be fully preserved through the welding thermal cycle. The study confirms that the SLM HAZ undergoes partial melting and recrystallization, effectively erasing the fine cellular structure within approximately 100–150 µm of the fusion line. This raises the question of whether the benefits of SLM microstructure refinement are lost in the vicinity of the weld, potentially limiting the overall structural advantage of hybrid SLM-conventional manufacturing approaches.
Another critical issue is the thermal expansion mismatch between the two alloys. AlSi10Mg has a different coefficient of thermal expansion compared to 6061-T6, which can lead to residual stresses and potential distortion in the joint. The study does not appear to provide detailed residual stress measurements, which would be essential for fatigue assessment of the joint in service. Future work should incorporate residual stress mapping using neutron diffraction or X-ray synchrotron techniques to characterize the stress state across the entire joint cross-section.
Study Insights and Implications
This research demonstrates that TIG welding of SLM-AlSi10Mg to 6061-T6 is technically feasible, but the joint performance is limited by temper softening in the conventional alloy HAZ. For engineering applications, this means that the joint design must account for the reduced strength in the HAZ, and fatigue-critical applications would require additional strengthening measures such as post-weld T6 re-tempering of the 6061-T6 side or application of compressive residual stress through shot peening. The hybrid manufacturing approach offers significant design flexibility, but the welding engineer must carefully manage the metallurgical incompatibilities between the additively manufactured and conventionally fabricated materials. The findings underscore that the transition from conventional to hybrid manufacturing paradigms requires equally careful attention to welding metallurgy and process qualification as traditional dissimilar metal welding.