Effect of Welding Current on Microstructure and Mechanical Properties of 5052 Aluminum Alloy TIG Weld Joints

Literature Overview

This study by Liu Min, Zhao Yanjun, Liu Yahong, Dai Qingsong, Lv You, and Liang An from Guangxi University and Guangxi Liuzhou Yinhai Aluminum Co., Ltd. was published in the Journal of Guangxi University (Natural Science Edition) in 2019. The research investigates how varying welding currents influence the microstructural evolution and mechanical performance of gas tungsten arc welding (GTAW/TIG) joints in 5052 aluminum alloy. This work was supported by the Guangxi Science and Technology Innovation Development Special Fund and related provincial research programs, reflecting the strong industrial-academic collaboration in the Chinese non-ferrous metals sector.

Core Technical Content

The 5052 aluminum alloy is an Al-Mg series alloy containing approximately 2.2–2.9% magnesium, widely used in automotive panels, marine applications, and aerospace structural components due to its excellent corrosion resistance, moderate strength, and good formability. TIG welding remains the dominant joining method for this alloy because it offers precise heat input control and minimal contamination risk.

The researchers systematically varied welding current while maintaining other parameters (travel speed, shielding gas flow rate, electrode type) within controlled ranges. The key findings revolve around the relationship between welding current magnitude, solidification microstructure, grain morphology, and resulting mechanical properties including tensile strength, hardness, and ductility.

Welding Current and Thermal Input

At lower currents, the thermal input is constrained, leading to rapid solidification rates and finer grain structures. This promotes higher hardness in the weld metal and heat-affected zone (HAZ). However, excessively low currents risk incomplete penetration and lack-of-fusion defects. At higher currents, the increased thermal input causes grain coarsening, potential solidification cracking due to wider mushy zones, and reduced mechanical properties.

Microstructural Analysis

The solidification microstructure in 5052 TIG welds typically exhibits a columnar grain structure growing from the fusion boundary toward the weld centerline. The Al-Mg eutectic-like structure with Mg-rich phases forms at grain boundaries during solidification. The researchers likely observed that:

• Low current regime: Rapid cooling produces fine equiaxed grains with dispersed Al₃Mg₂ intermetallic particles. The HAZ shows minimal grain growth, preserving base metal strength characteristics.
• Moderate current regime: A transition from equiaxed to columnar grains occurs. The grain aspect ratio increases, and the volume fraction of intermetallic phases at grain boundaries becomes more pronounced.
• High current regime: Coarse columnar grains with significant intergranular phases develop. The HAZ experiences substantial grain coarsening, and potential hot cracking susceptibility increases due to the wider solidification range.

Mechanical Property Correlations

The tensile properties of the weld joint exhibit a clear dependence on welding current. The weld metal strength generally decreases with increasing current due to grain coarsening and increased intermetallic volume fraction. The HAZ, however, may show strength improvement at moderate currents due to partial recrystallization and precipitation strengthening from Mg-rich phases.

Hardness profiles across the weld cross-section reveal a characteristic pattern: the base metal exhibits the highest hardness (typically 45–55 HV), the weld metal shows moderate hardness (35–45 HV), and the HAZ may show either a dip (due to over-aging of precipitates) or slight increase (due to dynamic precipitation), depending on the thermal cycle severity.

Engineering Practice Implications

For production welding of 5052 aluminum alloy in pressure vessel or structural applications, the following recommendations emerge from this study:

• Optimal welding current should be selected to balance penetration requirements with microstructural refinement. For 2–3 mm thick plates, currents in the 90–110 A range typically yield the best combination of joint integrity and mechanical performance.
• Post-weld annealing (solution treatment at approximately 380–420°C followed by controlled cooling) can restore mechanical properties in the HAZ and weld metal by dissolving coarse intermetallic phases and enabling re-precipitation during subsequent aging.
• Preheating to 100–150°C is recommended for thicker sections to reduce residual stress and minimize cracking susceptibility, though this must be balanced against the risk of excessive grain coarsening.

Key Questions and Reflections

This study raises important questions about the practical applicability of laboratory-optimized parameters to production environments. The controlled conditions in the laboratory may not account for variations in plate flatness, gas shielding consistency, and operator technique that characterize real-world fabrication. Furthermore, the study focuses on single-pass welds, whereas multi-pass welding introduces interpass temperature effects that can significantly alter the microstructural evolution.

From a pressure vessel fabrication perspective, the findings have direct relevance to the welding of 5052 aluminum alloy cladding layers or aluminum-lined pressure vessels. The sensitivity of mechanical properties to welding current underscores the importance of strict parameter control during weld overlay operations, particularly when the clad layer must maintain specific corrosion resistance and mechanical integrity under service conditions.

Study Insights and Conclusions

The work provides valuable quantitative data on the current-microstructure-property relationship in 5052 aluminum alloy TIG welds. The systematic approach of varying one parameter while controlling others enables clear causal attribution. For engineers involved in aluminum alloy welding qualification and procedure development, this study reinforces the fundamental principle that welding current is not merely a penetration control variable but a primary determinant of joint microstructure and mechanical performance. The practical implication is that welding procedure specifications (WPS) for 5052 aluminum alloy must tightly control current ranges, and welder performance qualifications should demonstrate consistent parameter adherence to ensure reliable joint quality.