Which specifications of the external hexagon bolts? How to deal with the surface of grade 10.9 GB5783 external hexagon bolts?In fact, it is a bit similar to the gasket, it must be blackened by oxidation. The principle is to produce an oxide film on the metal surface to isolate the air and achieve the purpose of rust prevention.Blackening treatment can be used when the appearance requirements are not high. The surface blackening treatment of steel parts is also called blue.The bluing treatment is a chemical surface treatment. Its main function is to form a dense oxide film on the surface of the workpiece, prevent the workpiece from corrosion and rust, and improve the wear resistance of the workpiece. It is only a surface treatment and will not affect the internal organization. Produce any influence, it is not heat treatment, and it is fundamentally different from quenching.There are two commonly used methods for blackening treatment: the traditional alkaline heating blackening and the late normal temperature blackening.However, the blackening process at room temperature is not very effective for low carbon steel.The main components of blackening liquor are sodium hydroxide and sodium nitrite.The temperature required for blackening has a large tolerance, and a good surface can be obtained between 135 and 155 ℃, but the time required is somewhat lengthy.
 The second is electroplating-gold, silver, copper, tin, nickel, chromium and other metals are plated on the workpiece as needed. The appearance is the metal color of the plated. The salt spray test is more than 24 hours.Electro-galvanizing technology is a traditional metal coating treatment technology, which provides basic corrosion resistance for metal surfaces.Cadmium plating: Cadmium plating is a positive plating layer, mainly used for technical anti-corrosion.The main advantages are good solderability and suitable contact resistance.Due to its good lubrication properties, cadmium plating is often used in aviation, aerospace, navigation, and radio and electronic products.The coating plays a dual role of mechanical and chemical protection on the steel substrate, so its anti-corrosion performance is much better than that of the zinc coating.The cost of cadmium plating is high (about 5 times that of galvanizing), which causes serious environmental pollution, so it is not recommended to use it. Zinc plating is normally used instead.
 镀锌：镀锌是商业紧固件常用的镀层。它比较便宜,外观也较好看,可以有黑色、军绿色。然而,它的防腐性能一般,其防腐性能是锌镀(涂)层中低的。一般电镀锌中性盐雾试验在72小时之内,也有采用特殊封闭剂,使得中性盐雾试验达200小时以上,但价格贵,是一般镀锌的5~8倍。镀锌加工过程易产生氢脆,所以10.9级以上的螺栓一般不采用镀锌的处理.虽然镀后可以用烘箱去氢,但因钝化膜在60℃以上时将遭破坏,因此去氢须在电镀后钝化前进行。如此可操作性差,加工成本高。在现实中,一般生产厂不会主动去氢,除非特定客户的强制要求。镀锌的紧固件扭矩—预紧力一致性较差,且不稳定,一般不用于于重要部位的连接。为了改善扭矩—预紧力一致性,也可采用镀后涂覆润滑物质的方法改善和提高扭矩—预紧力一致性。