Commonly used etchants for electroplating pretreatment

One, sulfuric acid

At room temperature, the ability of sulfuric acid solution to dissolve metal oxides is weak. Increasing the concentration of the solution can not significantly improve the etching ability of sulfuric acid. When the concentration reaches 40% or more, the dissolving power of iron oxide is significantly reduced, and when it reaches 60% or more, the oxide scale can hardly be dissolved. Hot sulfuric acid has a strong ability to corrode the steel matrix and has a greater peeling effect on the oxide scale. However, when the temperature is too high, it is easy to cause over-corrosion and hydrogen embrittlement of the steel matrix. Therefore, it is generally only heated to 50~60C, not more than 75C, and appropriate corrosion inhibitors should be added. Steel parts are generally etched in a 10% 20% (volume ratio) sulfuric acid solution at a temperature of 40°C. When the iron content in the solution exceeds 80g/L and the ferrous sulfate exceeds 215g/L, the etching solution should be replaced.

Sulfuric acid solution is widely used for etching steel, copper and brass parts. It is used together with chromic acid and dichromate as a deoxidizer and deashing agent for aluminum. It is mixed with hydrofluoric acid, nitric acid or both to remove oxide scale on stainless steel. Sulfuric acid anodic etching is an effective method for removing oxide scale and ash from steel.

Second, hydrochloric acid

At room temperature, hydrochloric acid has a strong chemical dissolution effect on metal oxides, but it dissolves the steel matrix relatively slowly. The use of hydrochloric acid is not easy to cause corrosion and hydrogen embrittlement. Hydrochloric acid can effectively etch a variety of metals at room temperature. When the concentration and temperature are the same, the etching speed of hydrochloric acid is 1.5~2 times faster than that of sulfuric acid. The concentration of the hydrochloric acid etching solution is usually 20% to 80% (volume ratio) hydrochloric acid solution, which is carried out at room temperature. Some departments] also use concentrated hydrochloric acid and warm it appropriately.

Three, nitric acid

Nitric acid is an important component of many bright etching solutions. The mixture of nitric acid and hydrofluoric acid is widely used to remove heat-treated oxide scale on lead, stainless steel, nickel-based and iron-based alloys, titanium, zirconium and some cobalt-based alloys. The mixed acid of nitric acid and sulfuric acid can be used for gloss etching of copper and copper alloy parts.

Four. Hydrofluoric acid

Hydrofluoric acid can dissolve silicon-containing compounds. It also has good solubility for chromium and aluminum oxides. Therefore, hydrofluoric acid can be used for the etching of special materials such as castings and stainless steel parts. However, hydrofluoric acid is highly toxic and has strong volatility. Care should be taken when using it to prevent contact with human skin.

Five. Phosphoric acid

Phosphoric acid is widely used for rust removal of steel parts, mainly to remove rust before the coating of steel weldment assemblies. For example, 2% phosphoric acid, when the temperature is 80°C, is used for rust removal of steel parts. Phosphoric acid is mixed with nitric acid, sulfuric acid, acetic acid or chromic anhydride, and can be used for bright etching of metals such as aluminum, copper and steel.

VI. Sodium Bisulfate

Sodium bisulfate is an acid salt used in most dry etching solutions. It can replace sulfuric acid and make handling more convenient. In addition, alkaline etching can be used for aluminum-based and zinc-based parts.