Electrochemical Performance of Laser Welded and TIG Welded 08Al Steel Joints

Literature Overview

The research conducted by Zhang Zhimin, Zhang Hong, and Liu Jia from the School of Mechanical and Electrical Engineering at Changchun University of Science and Technology, published in 2017 in Applied Laser, investigates the electrochemical properties of 08Al steel joints produced by laser welding and TIG (GTAW) welding with filler wire. 08Al steel is a low-carbon aluminum-killed steel widely used in pressure vessels, pipelines, and structural applications due to its good formability, weldability, and adequate strength. The study addresses an important aspect of weld quality that is often overlooked in conventional mechanical property evaluation: the electrochemical behavior of welds, which directly influences corrosion resistance and long-term service performance in aggressive environments.

Material Background and Electrochemical Significance

08Al steel (Chinese standard, equivalent to approximately ASTM A516 Gr.70 or similar low-carbon steels with aluminum deoxidation) contains 0.08% carbon and 0.02–0.05% aluminum. The aluminum addition serves as a deoxidizer during steelmaking, producing a clean, fine-grained structure with good weldability. However, the welding process introduces microstructural heterogeneity that creates electrochemical potential differences between the weld metal, heat affected zone (HAZ), and base metal, establishing a galvanic coupling that can accelerate localized corrosion.

Material Zone	Typical Composition	Microstructure	Electrochemical Potential (vs. SCE)
Base metal	0.08C, 0.02-0.05Al	Fine ferrite-pearlite	-0.55 to -0.60 V
Weld metal (laser)	Similar to base + filler	Fine ferrite + acicular ferrite	-0.58 to -0.65 V
Weld metal (TIG)	Higher dilution, possible C enrichment	Coarse ferrite-pearlite	-0.55 to -0.62 V
HAZ (laser)	Slight grain coarsening	Fine-to-medium ferrite-pearlite	-0.57 to -0.63 V
HAZ (TIG)	Significant grain coarsening	Coarse ferrite-pearlite	-0.53 to -0.58 V

The electrochemical potential differences between these zones, while seemingly small (tens to hundreds of millivolts), are sufficient to drive galvanic corrosion in the presence of a conductive electrolyte. The zone with the more negative potential (anodic) will preferentially corrode, while the zone with the more positive potential (cathodic) will be protected.

Electrochemical Testing Methodology and Results

The electrochemical characterization typically involves potentiodynamic polarization testing, electrochemical impedance spectroscopy (EIS), and open circuit potential (OCP) measurements in simulated service environments such as 3.5% NaCl solution or acidic solutions.

Potentiodynamic Polarization Results:

Parameter	Base Metal	Laser Weld	TIG Weld	Laser HAZ	TIG HAZ
Corrosion potential Ecorr (V