Why Is Phosphate Removal Necessary for Weld Screws?

For weld screws—particularly those without surface coatings—phosphate removal is often an essential step to ensure

stable and reliable weld quality. This process is a critical part of both metal surface preparation and resistance welding best practices.

Although phosphating is widely used to enhance corrosion resistance and improve paint adhesion, the resulting phosphate layer is

electrically insulating. This insulating property disrupts current flow during resistance welding, reducing weld penetration and strength,

and may result in weak or incomplete welds. By removing the phosphate layer, electrical current can pass more effectively through the

contact surfaces, improving weld consistency and joint integrity.

In applications—especially in the automotive and industrial sectors—strict requirements govern the surface condition of weld zones. Any

surface treatment that hinders electrical conductivity is typically prohibited. Standards such as ISO 14373 (resistance spot welding),

SAE J429 (mechanical fasteners), and internal specifications from manufacturers like TOYOTA and FORD explicitly require phosphate-free,

conductive surfaces in weld areas to ensure proper weld quality and mechanical strength.

Thus, phosphate removal is not just a preparatory step—it is a vital part of the welding process that directly influences product performance,

reliability, and compliance with industry standards.