Powder-coated steel guardrails with wave pattern are produced using a zinc-plated powder coating process (including rust removal, phosphatization, and passivation). After the workpiece is pre-treated, this phosphatized film not only prevents rust but also enhances the adhesion of the powder coating. The surface of hot-dipped galvanized steel is quite smooth, and without the necessary surface treatment before powder coating, the coating can easily peel off or come loose. Therefore, proper surface treatment is still a must.