Yellowing of Weld Spots in Nut Projection Welding and Remedial Measures？

In nut projection welding, it is not uncommon for the weld spots to exhibit a yellowish discoloration after the welding process. This article addresses the causes behind the yellowing phenomenon and provides solutions to mitigate this issue, ensuring the production of high-quality welds.

Causes of Yellowing:

1. Oxidation: The yellowish coloration can occur due to the oxidation of the weld spot during the welding process. Factors such as inadequate shielding gas coverage or improper cleaning of the workpiece surface can lead to increased exposure to oxygen, resulting in oxidation.
2. Contamination: Presence of contaminants, such as oil, grease, or surface coatings on the workpiece or nut, can contribute to the yellowing of the weld spots. These contaminants can undergo thermal degradation during the welding process, leading to discoloration.
3. Excessive Heat: Excessive heat input or prolonged welding time can also cause discoloration of the weld spots. Overheating can result in the formation of intermetallic compounds or changes in the microstructure, leading to a yellowish appearance.

Solutions to Address Yellowing:

1. Proper Cleaning: Thoroughly clean the workpiece and nut surfaces before welding to remove any contaminants. Utilize appropriate cleaning methods, such as degreasing or solvent cleaning, to ensure a clean and contamination-free surface.
2. Adequate Shielding Gas: Ensure sufficient shielding gas coverage during the welding process to minimize exposure to atmospheric oxygen. This can be achieved by adjusting the gas flow rate, optimizing the nozzle position, or utilizing gas cups or shrouds to enhance gas shielding.
3. Optimize Welding Parameters: Adjust the welding parameters, such as current, voltage, and welding time, to achieve an optimal balance between heat input and weld quality. Avoid excessive heat that can lead to discoloration by optimizing the parameters based on the material type and thickness.
4. Evaluate Material Compatibility: Verify the compatibility between the workpiece material, nut material, and any surface coatings. Incompatible materials or coatings can undergo undesirable reactions during welding, leading to discoloration. Select compatible materials or consider removing incompatible coatings before welding.
5. Post-Weld Cleaning: After completing the welding process, perform post-weld cleaning to remove any flux residues or spatter that could contribute to discoloration. Utilize appropriate cleaning methods based on the specific requirements of the application.

The yellowing of weld spots in nut projection welding can be attributed to oxidation, contamination, or excessive heat. By implementing proper cleaning practices, ensuring adequate shielding gas coverage, optimizing welding parameters, evaluating material compatibility, and performing post-weld cleaning, manufacturers can effectively mitigate the issue of yellowing and achieve high-quality welds. Regular monitoring of the welding process and adherence to best practices will help ensure consistent weld appearance and overall product quality.