To improve the corrosion resistance of phosphating fasteners, PF-MIAM and PF-MIAR phosphating solutions were used after comparing with various phosphating solutions. The composition and ratio of the solution have a great influence on the quality of phosphating. When the self-adjusting calcium salt phosphating solution is used for production, the phosphating film formed on the surface of the workpiece has coarse crystals, a lot of ash, and the appearance quality of the product is poor. The prepared black phosphating liquid produces relatively more sediments, and it is necessary to beat the waterlogged sediment basically every day.

Too high total acidity will make the film too thin, and too low total acidity will make the film loose and rough. Acid ratio refers to the relationship between free acidity (Tb) and total acidity (Ta). If the free acidity is too high, the interaction with steel parts is fast, and a large amount of hydrogen will be evolved, which will make the interface layer phosphate not easily saturated, resulting in difficulty in the formation of crystal nuclei, coarse crystals, loose and porous films, reduced corrosion performance, and phosphating time. Prolonged; the free acidity is too low, the phosphating film is thin, or even no phosphating film is formed.

The main component of the solution is low: add the main solution. The acid ratio is incorrect: the free acidity is too high, it can be adjusted by adding manganese carbonate; the total acid is too low, it can be adjusted by adding the main agent, and the total acid can be controlled above 85 points. Poor solution composition ratio: Improve the formula of phosphating solution and use PL-VM phosphating solution.

Using PL-VM phosphating solution, the adjustment of solution parameters is simple, the sediment is less, the workpiece is hung with ash, the film layer is finely crystallized, the neutral salt spray resistance time can be improved, and the corrosion degree of the workpiece after the neutral salt spray test is small.

The composition of the self-prepared phosphating solution is not well controlled, the solution adjustment is difficult, there is a lot of precipitation, and the workpiece hangs in the ash, and the workpiece is easily corroded during the phosphating process.