CLADDING TECHNOLOGY SHANXI CO., LTDTIG Arc Compound Droplet Deposition Additive Manufacturing of 45 Steel Lead Alloy Bimetallic Structure
Literature Overview
Published in Materials Review (材料导报) in 2022, this research from Xi'an Jiaotong University investigates the additive manufacturing of a 45 steel/lead alloy bimetallic structure using TIG arc compound droplet deposition. The work by Du Jun, Jiang Minbo, Zhang Yongheng, Xu Siyuan, and Wei Zhengying is supported by the National Natural Science Foundation of China (Grant No. 51775420) and a civil aerospace pre-research project (D020208). This study addresses a unique challenge in bimetallic manufacturing: combining a structural steel with a soft, low-melting-point lead alloy through arc-based processes.
Technical Challenges and Process Design
The combination of 45 steel (melting point ~1495°C) and lead alloy (melting point ~327°C) presents extreme metallurgical challenges:
| Challenge | Root Cause | Countermeasure |
|---|---|---|
| Extreme melting point difference | 1168°C ΔT | Compound droplet feeding |
| Intermetallic compound formation | Fe-Pb immiscibility | Rapid solidification, thin layers |
| Dilution control | Density and melting differences | Independent wire feed control |
| Bond strength | Weak Fe-Pb interface | Optimized thermal cycling |
| Layer adhesion | Thermal stress from CTE mismatch | Low heat input, controlled cooling |
The "compound droplet deposition" technique involves feeding both materials simultaneously through a single or dual-wire configuration, where the arc melts the wires and deposits them in a controlled manner. The key innovation is the ability to create layered or gradient interfaces between the two dissimilar materials.
Process Parameters and Microstructural Control
The process parameters identified in this study include:
- Arc current: 120–180 A (lower than conventional TIG to minimize thermal input)
- Travel speed: 300–500 mm/min (high speed to limit interdiffusion)
- Lead wire feed rate: 3–6 m/min
- Steel wire feed rate: 2–4 m/min
- Shielding gas: 99.99% Ar with 2–5% H₂ (to reduce surface tension and improve wetting)
The microstructural analysis reveals a complex interface consisting of:
- A thin diffusion zone (5–20 μm) with possible Fe₂P and other intermetallic phases
- A lead-rich zone with dispersed steel particles
- A steel matrix with lead inclusions in the transition region
- Sound weld microstructure in the bulk steel and lead regions
Engineering Applications and Study Insights
This bimetallic structure concept has applications in radiation shielding (lead for gamma shielding, steel for structural support), bearing surfaces (lead for low-friction, steel for load-bearing), and aerospace thermal management (lead for thermal mass, steel for structural integrity). The civil aerospace pre-research funding indicates potential applications in spacecraft radiation shielding or thermal protection systems.
From a quality assurance perspective, this process requires careful attention to:
- Interface bond strength testing (shear and tensile tests)
- Intermetallic phase mapping (SEM-EDS analysis)
- Thermal cycling fatigue assessment
- Dimensional stability under thermal gradients
The study demonstrates that arc-based additive manufacturing can create bimetallic structures that would be impossible through conventional casting or bonding methods, opening new possibilities for functionally graded materials and multi-material components. However, the narrow process window and sensitivity to parameter variations require robust monitoring and control systems for reliable production.