Answer
Zinc Phosphate coating (often called 'Parkerizing') is a common surface treatment for carbon steel wave springs in automotive transmissions. It provides a moderate level of corrosion resistance and acts as an excellent base for supplemental lubricants or oils. The process involves immersion in a phosphoric acid solution containing zinc ions, which reacts with the steel to form a crystalline layer of zinc phosphate. Unlike electroplating, zinc phosphate is not associated with significant hydrogen embrittlement risks. Moreover, the crystalline structure is porous, allowing it to 'hold' oil, which provides critical 'boundary lubrication' during the initial break-in period of the transmission, reducing wear on the wave crests as they seat against the mating gears.
