CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Mechanical Properties of 5356 Aluminum Alloy TIG Arc Additive Manufacturing
Literature Overview
The 2021 study by Sun Jiaxiao, Yang Ke, Wang Qiuyu, Ji Shanlin, Bao Yefeng, and Pan Jie, conducted jointly by Hohai University and the Shenyang Institute of Metal Research under the State Key R&D Program, investigates the microstructure evolution and mechanical properties of 5356 aluminum alloy deposits produced by TIG arc additive manufacturing. This work represents a significant advancement in understanding how wire-fed arc additive manufacturing (WAAM) can produce functional aluminum alloy components with controlled microstructures and properties, funded under project No. 2017YFE0100100 and supported by Changzhou municipal research program No. CE20205046.
Core Technical Content
5356 aluminum alloy (AlMg4.5) is a high-strength, corrosion-resistant aluminum alloy known for its excellent weldability due to the absence of copper, which minimizes hot cracking susceptibility. The TIG arc additive manufacturing process deposits material layer by layer using a continuously fed 5356 wire electrode, with each layer solidifying rapidly under the influence of the preceding layer acting as a heat sink. The thermal cycling in WAAM is fundamentally different from conventional welding: each subsequent layer reheats the previously deposited material, creating a complex thermal history that results in a unique microstructure.
Microstructural Evolution
The deposited microstructure of 5356 WAAM typically consists of fine equiaxed alpha-aluminum grains with dispersed beta-phase Al3Mg2 precipitates. The rapid solidification rates, often exceeding 10 to 50 K/s near the fusion boundary of each layer, promote fine grain formation. However, the interpass reheating causes grain growth and precipitate coarsening in the lower layers. The authors identified three distinct microstructural zones: the fusion zone with fine columnar grains, the HAZ with mixed columnar and equiaxed grains, and the base metal or previously deposited layers with coarser equiaxed grains.
The mechanical properties show a gradient through the build height. The top layers, which experience less interpass reheating, exhibit higher strength and hardness, with tensile strength reaching 280 to 320 MPa and hardness of 80 to 95 HV. The bottom layers, subjected to multiple thermal cycles, show reduced strength of 220 to 260 MPa and hardness of 65 to 80 HV due to grain coarsening and precipitate over-aging.
Process Parameters and Their Influence
| Parameter | Range | Effect on Microstructure |
|---|---|---|
| Wire feed speed | 4 to 8 m/min | Higher speed increases deposition rate but may reduce penetration |
| Travel speed | 200 to 500 mm/min | Slower speed increases heat input and grain size |
| Arc current | 150 to 250 A | Higher current increases melt pool depth and dilution |
| Interpass temperature | 150 to 300 degrees C | Higher temperature promotes grain growth and precipitate coarsening |
| Layer thickness | 1.5 to 3.0 mm | Thinner layers provide better heat dissipation and finer grains |
The interpass temperature is particularly critical in WAAM of 5356 aluminum alloy. Maintaining interpass temperatures below 200 degrees Celsius is recommended to minimize grain coarsening and preserve the fine precipitate distribution. The authors demonstrated that controlling the interpass temperature through active cooling or strategic layer sequencing can improve the mechanical uniformity through the build height by up to 25 percent.
Engineering Implications and Reflections
This study has profound implications for the emerging field of arc additive manufacturing of aluminum alloy components. The key challenge identified is the mechanical property gradient through the build height, which arises from the inherent thermal cycling in the WAAM process. For pressure vessel and structural applications, this gradient must be accounted for in design calculations, as the weakest layer may govern the component's load-bearing capacity.
The work also highlights the advantage of 5356 as a WAAM material compared to other aluminum alloys. The absence of copper eliminates hot cracking concerns, and the Mg content provides adequate strength without the brittleness associated with high-copper alloys. However, the relatively low strength of as-deposited 5356 WAAM builds compared to wrought 5356 plate (which can reach 350 to 400 MPa in the O temper) suggests that post-build heat treatment may be necessary for demanding applications.
Study Insights
The fundamental insight from this research is that WAAM microstructure is governed by the interplay between solidification rate and interpass thermal cycling, and that controlling the latter through process design is essential for achieving uniform properties. For engineering practice, this means that WAAM process development for aluminum alloys must incorporate thermal modeling and interpass temperature control strategies from the outset, rather than treating them as secondary concerns. The work also demonstrates that even with relatively simple equipment such as a standard TIG welding power source, significant microstructural control is achievable through careful parameter optimization.