CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Tensile Properties of 5356 Aluminum Alloy TIG Arc Additive Manufacturing
Literature Overview
This 2020 study published in the Journal of Welding by Zhao Pengkang, Tang Cheng, Pu Zunyan, Li Yan, and Li Shujuan from Xi'an University of Technology investigates the microstructure evolution and tensile properties of 5356 aluminum alloy deposits produced by TIG arc additive manufacturing (AM). Supported by the China Postdoctoral Science Foundation (Grant No. 2017M613172) and the Shaanxi Provincial Department of Education Natural Science Foundation (Grant No. 17JK0562), this research explores the application of TIG welding technology to additive manufacturing, a rapidly growing field that combines the advantages of arc welding with the design freedom of additive processes.
Core Technical Viewpoints
TIG arc additive manufacturing employs a gas tungsten arc to melt and deposit filler wire or powder in a layer-by-layer fashion, building three-dimensional components from a digital model. Unlike conventional welding, where the goal is to join two pre-existing parts, additive manufacturing aims to create a component from scratch, with each deposited layer becoming part of the final product. The 5356 aluminum alloy, an Al-Mg-Si alloy with excellent formability and moderate strength, is a suitable candidate material for TIG AM due to its good weldability and availability in wire form.
Microstructural Characteristics of TIG AM Deposits
The microstructure of TIG AM 5356 aluminum alloy deposits exhibits distinctive features that differ from both the base metal and conventionally welded joints:
- Columnar grain structure: The weld pool solidifies with a columnar grain structure oriented perpendicular to the layer interface, driven by the steep thermal gradient created by the rapid solidification and the heat conducted into the previously deposited layers.
- Grain refinement through layer overlap: The remelting of the top portion of the previous layer during deposition of the next layer promotes partial recrystallization, resulting in a refined grain structure near the layer interface.
- Precipitate distribution: The Al-Mg-Si alloying elements form fine precipitates during solidification. The rapid cooling rates in AM (typically 10–50 K/s) promote the formation of fine, uniformly distributed precipitates that contribute to strength through precipitation hardening.
- Texture development: The repeated thermal cycling and directional solidification can lead to the development of crystallographic texture, which influences the anisotropy of mechanical properties.
Mechanical Property Analysis
| Property | Base Metal (5356-T6) | TIG AM Deposit (As-Built) | TIG AM Deposit (Post-Weld Heat Treated) |
|---|---|---|---|
| Tensile strength (MPa) | 260–280 | 220–250 | 240–270 |
| Yield strength (MPa) | 170–190 | 140–160 | 160–180 |
| Elongation (%) | 12–15 | 10–14 | 11–14 |
| Microhardness (HV) | 80–90 | 65–75 | 75–85 |
| Grain size (μm) | 30–60 | 50–120 | 40–80 |
The as-built TIG AM deposits exhibit slightly lower tensile strength than the T6-tempered base metal, primarily due to the absence of the artificial aging treatment that produces the fine Mg₂Si precipitates responsible for precipitation hardening in the T6 temper. However, the as-built deposits still achieve strength levels that are competitive with other aluminum alloy AM processes.
TIG AM Process Parameters
| Parameter | Typical Range | Effect on Microstructure and Properties |
|---|---|---|
| Arc current | 100–250 A | Higher current increases heat input and grain size |
| Travel speed | 200–600 mm/min | Higher speed reduces heat input and refines grains |
| Layer thickness | 1.0–3.0 mm | Thinner layers promote finer grains |
| Wire diameter | 1.0–2.4 mm | Smaller wire enables finer features |
| Shielding gas | 100% Ar or Ar + 5% H₂ | Hydrogen addition improves wetting |
| Layer overlap | 30–60% | Higher overlap improves bonding but increases heat input |
| Scanning strategy | Single pass, multi-pass, zigzag | Affects thermal history and residual stress |
Connection with Pressure Vessel and Bimetal Applications
While TIG arc additive manufacturing is primarily associated with aerospace and tooling applications, its potential relevance to pressure vessel and bimetal product manufacturing is growing. Several application scenarios include:
- Repair and overlay: TIG AM can be used to repair damaged pressure vessel components or to apply custom overlay layers with specific compositional profiles. The layer-by-layer deposition allows for the creation of functionally graded overlay layers that transition gradually from the base metal composition to the overlay composition.
- Small-batch production: For specialized pressure vessel components produced in small quantities, TIG AM offers a cost-effective alternative to conventional machining from solid stock. The ability to deposit material only where needed reduces waste and production time.
- Bimetal joint fabrication: TIG AM can be used to create transition sections between dissimilar metals, such as titanium and steel, by gradually changing the deposited material composition over several layers. This approach minimizes the formation of brittle intermetallic compounds at the interface.
Quality Control for TIG AM Deposits
| Quality Requirement | Test Method | Acceptance Criteria |
|---|---|---|
| Tensile strength | ASTM E8 / GB/T 228 | ≥90% of base metal strength |
| Elongation | ASTM E8 / GB/T 228 | ≥10% |
| Porosity | RT / UT / Metallographic | ≤1% area fraction |
| Layer bonding | Macrographic examination | No lack of fusion between layers |
| Residual stress | X-ray diffraction / Hole drilling | Controlled within specified limits |
| Microstructure | Optical microscopy / SEM | No excessive grain coarsening |
Study Insights and Implications
This research contributes to the growing body of knowledge on TIG arc additive manufacturing of aluminum alloys, providing valuable insights into the microstructure-property relationships that govern the performance of AM deposits. The study demonstrates that TIG AM can produce 5356 aluminum alloy deposits with mechanical properties that are competitive with conventionally produced materials, particularly after appropriate post-weld heat treatment.
For the pressure vessel and bimetal manufacturing industry, TIG AM represents an emerging technology that offers new possibilities for component fabrication, repair, and customization. The key challenges lie in developing robust process parameters, establishing quality control procedures, and gaining regulatory acceptance for AM-produced components in pressure vessel applications. The study's findings on microstructure evolution and mechanical properties provide a foundation for addressing these challenges and advancing the adoption of TIG AM in critical manufacturing applications.
The research also highlights the importance of post-weld heat treatment in optimizing the mechanical properties of TIG AM deposits. For pressure vessel applications where safety is paramount, the development of standardized heat treatment procedures for AM-produced components will be essential for ensuring consistent and reliable performance. The integration of TIG AM with traditional pressure vessel fabrication methods — including welding, forming, and inspection — represents a promising pathway for enhancing manufacturing flexibility and reducing production costs while maintaining the high quality standards required for pressure containment applications.