MIG Welding for Marine Aluminum Alloys
MIG welding is mainly used for welding aluminum alloys, stainless steel and some low-alloy steels. In order to obtain good welding quality and high productivity, the following three aspects should be considered: pre-welding preparation and good gas protection effect, a reasonable droplet transition form and process parameters, and reasonable welding equipment and welding process procedures.
Aluminum can oxidize at any temperature, forming an oxide film Al2O3 on its surface. The oxide film has a high melting point and is insoluble in liquid metal, which hinders the normal fusion of the weld, deteriorates the weld formation and the quality of the joint. Since hydrogen can be dissolved in a large amount in molten aluminum, it is easy to cause pores, especially marine aluminum alloys, which are more likely to generate pores during welding.
When the thickness of aluminum and its alloy workpiece exceeds 4mm, metal argon arc welding (MIG) is a more economical and efficient welding method. The rigidity of pure aluminum and aluminum alloy welding wire is worse than that of steel welding wire. Therefore, the diameter of the aluminum mig welding wire used for aluminum alloy MIG welding should not be less than 1.5mm, and the welding current should be greater than 130-140A to ensure the current density required for jet transition.
When welding aluminum and its alloys with metal argon arc welding (MIG), gas protection must be reliable. The purity of argon gas is required to be high (>99.8%), and the welding wire and groove must be carefully cleaned. After cleaning, in order to prevent the oxide film from re-forming on the surface of the welding wire and hydrogen adsorption, the cleaned welding wire must be used within 8 to 12 hours.
The cleaned aluminum mig wire can also be placed in a sealed package filled with argon for storage. The welded base material is generally cleaned mechanically, and generally used no more than 3 to 4 days and nights after cleaning.
Welding aluminum and its alloys usually uses AC or DC reverse polarity. When welding medium and thin plates, pure argon is used for protection; when welding thick and large pieces, Ar+(50-60)%He mixed gas is used for protection.
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