In order to improve the corrosion resistance and performance, the fastener bolt need to process with surface treatment. Different quality requirements, different surface treatment.
1.Zinc plating
Galvanic zinc plating is the most commonly plating for commercial fastener bolt. It is relatively cheap and has a good appearance. However, the corrosion resistance of galvanic zinc plating is the lowest among zinc plating.
The neutral salt spray test for galvanic zinc plating is usually within 72 hours, but special sealers are also used to make the neutral salt spray test more than 200 hours. Galvanized zinc process is prone to hydrogen embitterment, so more than 10.9 grade bolts are not advised to undergo galvanic zinc plating
2.Phosphating
The corrosion resistance of phosphating is worse than galvanizing zinc plating. After phosphating, the fastener bolt will be coated with oil which will influence the the corrosion resistance of bolt. In neutral salt spray test, high-grade anti-rust oil can be more effective than general anti-rust oil. Besides, high-strength bolts with phosphating can avoid hydrogen embitterment, so bolt over 10.9 grade always choose phosphating surface treatment.
3.Oxidation
Oxidation with oiling is a very popular coating for industrial fasteners because it is the cheapest and looks good until the oil runs out. As oxidation without rust protection, it will rust quickly. The neutral salt spray test is only 3 to 5 hours in the oiled condition.
4.Cadmium plating
The corrosion resistance of cadmium plating is better than other surface treatment, especially in the condition of marine atmosphere. However, its price is about 15-20 times more than zinc plating. Therefore, it is only used in certain environments such as oil drilling platforms and seafaring aircraft.
5.Chrome plating
Chrome plating is very stable with high hardness and good wear resistance. For fastener bolt, chrome plating usually plays the role of decoration. The price of well-performed chrome plating fasteners is as expensive as stainless steel. Only when the strength of stainless steel is not enough, chrome plating fastener will be adopted.
