Flux: in the welding process can help and promote the welding process, also has protective effect, prevent the oxidation reaction of chemical substances. The flux can be divided into solid, liquid and gas. The main "auxiliary heat conduction", "to remove the oxide", "reduce welding material surface tension", "be removed welding material surface oil, increasing the welding area", "prevent reoxidation" and so on several aspects, in the key role of two is: "to remove the oxide" and "reduce welding material surface tension.