Why does the zipper corrode after repeated laundering?

Q: Why does the zipper corrode after repeated laundering? Repeated laundering exposes metal parts to detergent, water and heat, and corrosion often appears first at scratches and cut edges. Comparing a washed sample with an unwashed control from the same lot shows whether the wash route or the finish is responsible. Identify the corroded parts and whether corrosion follows wear marks. Review detergent type, dosage and whether bleach was used. Check drying method and temperature against the maker's guidance. Compare a washed sample with an unwashed control from the same lot. Inspect plating or coating on the corroded parts for breaks. Corrosion at wear points after many washes is a finish durability question and should be discussed with the maker using the wash count and detergent details. Corrosion on unused parts out of the pack is a supply issue. A care trial at the intended wash condition is the practical way to set expectations before bulk production.