Phosphating (also known under the trade name as Parkerizing™) is the chemical deposition of zinc or manganese onto a part. The difference between the two types is primarily in the grain size of the crystals created during the process. The zinc phosphate tends to be a finer crystalline pattern, while manganese phosphate produces one that is more course. These patterns create more surface area on the part and an improved anchor profile for better adhesion for a subsequent coating. They also provide increased corrosion protection when applied with another coating. Below are some common specifications that are often called out:

MIL-P-16232
Type Z: Zinc phosphate coating

Class 1: Supplementary preservative treatment or coating as specified
Class 2: Supplementary treatment with preservative conforming to MIL-C-
16173 Grade 3 or MIL-L-3150 as alternative for very small parts
Class 3: No supplementary treatment

Type M: Manganese phosphate coating

Class 1: Supplementary preservative treatment or coating, as specified
Class 2:Supplementary treatment with lubricating oil conforming to MIL-L-3150
Class 3: No supplementary treatment

Benefits
• Prolong the life of organic coating
• Provide good paint bonding
• Improve corrosion resistance by providing a good base for absorbing and retaining rust preventative materials
• Provide an excellent base for holding lubricants and drawing compounds