Microstructure of phosphate conversion film formed on the surface of A36 steel prepared by micro-arc discharge plasma

Abstract

Phosphate conversion film is an important surface protection film for steel. It mainly has the functions of corrosion resistance, wear resistance, plastic processing lubricity, etc., or as the basis of subsequent coating or painting. Phosphate treatment is traditionally used to form a Phosphate conversion film on the surface of steel. In this treatment method, a dilute solution of phosphoric acid and phosphate can be applied to the surface to be treated by spraying or soaking, so that it can react with the surface to form an insoluble phosphate film. This method is more difficult to control the thickness and microstructure of the formed film, and there are many pretreatment procedures. In response to future environmental policies, carbon neutrality and 2050 net zero carbon emissions must be met. In this study, the micro-arc discharge method was used from the surface pretreatment of A36 steel to the formation of the phosphoric acid film. The consistent method shortened the process steps and reduced the carbon emission of the process to comply with the environmental policy. The discharge voltage is 50 ∼ 200 V, the current is about 1.6 A, and the different process time and current are controlled, which to observe the microstructure of the phosphoric acid film and surface hardness. Possible reaction mechanisms for phosphate film formation will be discussed in this paper.