What are the functions and practices of surface treatment methods in the corrosion resistance of Carbon Steel Screws?

Carbon steel screws have poor corrosion resistance because carbon steel is inherently prone to oxidation and will rust quickly when exposed to air, moisture or corrosive environments. To improve the corrosion resistance of carbon steel screws, a protective layer is often added to the surface of the screws through various surface treatment techniques. These treatments not only slow down the corrosion process of the screws, but also enhance their mechanical properties and aesthetics.

Galvanizing is the most common anti-corrosion treatment for carbon steel screws. It prevents rust by covering the surface of the screw with a layer of zinc to prevent the iron element from reacting with oxygen and moisture in the air. Zinc acts as a sacrificial anode, and even if part of the coating on the surface of the screw is damaged, the zinc will still be preferentially oxidized to protect the underlying steel.

Place the carbon steel screw in a solution containing zinc salts, and deposit a zinc layer on the surface of the screw through an electrolytic reaction. This method is simple to operate and low in cost, but the coating is thin and suitable for indoor use. Immerse the screw in molten zinc liquid to form a thicker zinc layer. Hot-dip galvanizing has better corrosion resistance than electroplating and is suitable for outdoor or harsh environments.

Nickel and chromium have excellent corrosion resistance and decorative properties. Nickel plating and chromium plating can form a dense metal protective layer on the surface of the screw to prevent the underlying steel from contacting corrosive substances. At the same time, the high hardness of the nickel and chromium plating layers can enhance the wear resistance and durability of the screws.

The screws are placed in an electrolyte containing nickel salts, and the nickel layer is deposited on the surface of the screws using an electric current. The nickel plating layer is smooth and bright, and has good anti-corrosion and anti-oxidation effects. Similar to the nickel plating process, chromium plating is mostly used for industrial and decorative needs. The chromium layer is not only corrosion-resistant, but also maintains good performance in high temperatures and harsh environments.

Phosphating is a chemical conversion treatment that provides basic corrosion protection by forming a solid phosphate film on the surface of the screw. The phosphate film can absorb lubricating oil or paint, further enhancing the anti-corrosion ability and lubrication effect of the screw.

The screws are immersed in an acidic solution containing phosphates, a chemical reaction occurs, and a phosphate film with a microporous structure is formed on the surface. The phosphate layer itself does not have a strong corrosion resistance, but the overall anti-corrosion effect can be improved through subsequent paint, coating or lubricating oil treatment.

Dacromet is an inorganic coating based on zinc and aluminum. It has strong corrosion resistance and can withstand corrosion erosion in harsh environments. Compared with traditional zinc plating, Dacromet coating is thinner, but the anti-corrosion effect is better than ordinary electroplating.

The screw is immersed in a solution containing zinc and aluminum particles, and then cured at high temperature to form a dense coating. This coating not only has good corrosion resistance, but also has high temperature resistance, chemical resistance, and good adhesion and toughness.

Carbon steel screws must be improved through a variety of surface treatment technologies due to their inherent lack of corrosion resistance. Common surface treatment methods include galvanizing, nickel or chrome plating, phosphating, Dacromet coating, black oxide treatment, and spray coating. Each method has its own unique advantages, and the choice of which treatment method depends on the specific application environment of the screw and the requirements for corrosion resistance.