How does an electrochemical workstation evaluate corrosion resistance of welded joints? Expert Testing Guide

An electrochemical workstation evaluates corrosion resistance by subjecting a welded sample to potentiodynamic polarization tests within a corrosive medium. By utilizing a precise three-electrode system, the device applies a range of voltages to the dissimilar metal joint and measures the resulting current flow in real-time. This process generates quantitative data regarding the sample's self-corrosion potential and current density, allowing for a direct assessment of chemical stability.

The core value of this method lies in its ability to isolate the behavior of specific zones—the weld zone, heat-affected zone, and base material. It translates the complex chemical interactions of dissimilar metals into measurable electrical signals, predicting how well the joint will maintain its protective passivation layer or resist pitting.

The Three-Electrode Measurement System

The Circuit Configuration

To ensure accuracy, the workstation does not rely on a simple two-point measurement. It employs a three-electrode system to isolate the variables.

The Specific Roles of the Electrodes

The system includes a platinum electrode (auxiliary) to conduct current and a saturated calomel electrode (reference) to provide a stable baseline voltage. The welded joint itself serves as the working electrode (specimen).

Real-Time Monitoring

The workstation monitors the electrochemical response instantly as voltage is applied. This captures the dynamic changes in the metal's surface chemistry as it interacts with the corrosive environment.

Key Metrics for Evaluation

Self-Corrosion Potential

The workstation measures the self-corrosion potential, which indicates the thermodynamic tendency of the metal to corrode. A more negative potential generally suggests the material is more active and prone to corrosion.

Corrosion Current Density

Simultaneously, the device calculates the corrosion current density. This metric is critical because it represents the actual kinetic rate of corrosion—how fast material is being lost.

Passivation Behavior

The test evaluates the material's ability to form a stable, protective oxide layer (passivation). Breaks or instabilities in the current flow can indicate where this protective film is failing.

Analyzing the Dissimilar Joint Zones

Differentiating the Zones

Dissimilar metal welds are not uniform; they consist of the base material, the heat-affected zone (HAZ), and the weld zone. The workstation allows you to analyze the specific corrosion behavior of each distinct region.

Identifying the Weakest Link

By comparing the current density across these zones, you can identify which area is most susceptible to degradation. Often, the HAZ is the most vulnerable due to thermal changes during welding.

Pitting Resistance

The potentiodynamic scan pushes the material until localized breakdown occurs. This effectively quantifies the joint's pitting resistance, revealing how likely it is to suffer from deep, localized holes rather than uniform surface corrosion.

Understanding the Limitations

Destructive Nature of Testing

While highly informative, potentiodynamic polarization is often a destructive test. The high potentials applied can permanently alter the surface of the specimen or induce severe pitting during the analysis.

Sensitivity to Surface Preparation

The accuracy of the workstation is heavily dependent on the surface finish of the specimen. Improper polishing or cleaning of the weld can introduce artifacts that the machine interprets as corrosion activity.

Making the Right Choice for Your Project

To maximize the utility of an electrochemical workstation for welded joints, align the data with your specific engineering goals:

• If your primary focus is galvanic compatibility: Look for large differences in self-corrosion potential between the base metals and the weld zone, as these gaps drive galvanic corrosion.
• If your primary focus is service life prediction: Prioritize the corrosion current density data, as this provides the most direct calculation of material loss rates over time.
• If your primary focus is environmental resilience: Examine the passivation region of the polarization curve to ensure the protective oxide layer remains stable under high potentials.

By systematically analyzing these electrochemical signals, you move beyond guesswork and ensure the chemical integrity of your dissimilar metal connections.

Summary Table:

Evaluation Metric	Description	Critical Insight
Self-Corrosion Potential	Thermodynamic tendency to corrode	Indicates material activity & galvanic compatibility.
Corrosion Current Density	Kinetic rate of material loss	Predicts the actual speed of corrosion/service life.
Passivation Behavior	Stability of protective oxide layer	Determines environmental resilience and pitting resistance.
Zone Analysis	Comparing Weld, HAZ, and Base Metal	Identifies the weakest structural link in the joint.

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References

1. M. Dziekońska, T. Jung. Microstructure and Properties of Dissimilar Joints of AISI 430 Steel with Inconel 625 Obtained by Electron Beam Welding. DOI: 10.12913/22998624/152529

This article is also based on technical information from Kintek Solution Knowledge Base .