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Characteristics and methods of welding aluminum and aluminum alloy pipes

Aluminum alloy is widely used in various welded structural products due to its light weight, high strength, good corrosion resistance, non-magnetic, good formability and good low temperature performance. Aluminum alloy is used instead of steel plate material to weld, and the structure weight can be Reduce by more than 50%. Therefore, in addition to being widely used in aviation, aerospace, and electrical engineering, aluminum and aluminum alloys are also increasingly used in the petrochemical industry.

Since aluminum and aluminum alloy pipes conduct heat quickly and the molten pool crystallizes quickly, there should be no gaps or blunt edges during assembly, and forced processing should be avoided to reduce the large residual stress after welding. The length of the positioning weld is 10-15mm.

Before welding, remove the black powder and oxide film on the surface of the tack welding, and repair the two ends to a gentle slope. The weldment does not need to be preheated. Test welding on the test board before welding. When it is confirmed that there is no porosity, perform the formal welding. Use high-frequency arc ignition, the arc starting point should cross the center line about 20mm, and stay there for about 2-3 seconds, and then, under the condition of ensuring the penetration, use high current, fast welding, the welding wire does not swing, and the end of the welding wire is not Should leave the argon protected area. If leaving the argon gas protection zone, the end of the welding wire should be cut off. The angle between the welding wire and the surface of the weld should be about 15°, and the angle between the welding gun and the surface of the weld should be kept between 80° and 90°.

In order to increase the argon protection zone and enhance the protection effect, a large-diameter welding gun porcelain nozzle can be used to increase the argon flow of the welding gun. When spatters that obstruct the flow of argon gas are attached to the nozzle, the spatters must be removed or the nozzle must be replaced. When the tungsten tip is contaminated, the shape is irregular, etc., it must be repaired or replaced. The tungsten electrode should not stick out of the nozzle. The control of welding temperature is mainly the control of welding speed and welding current.

The test results show that high-current, fast welding can effectively prevent the generation of pores. This is mainly due to the faster penetration of the weld during the welding process, the short heating time of the molten metal, and the less chance of gas absorption. When closing the arc, pay attention to filling the arc crater, reducing the molten pool, and avoiding shrinkage holes. The junction of the end point should be welded by 20~30mm. After stopping the arc, delay the gas stop for 6 seconds. When the rotating aluminum and aluminum alloy pipes are butt welded, the welding torch should be in a slightly upward slope welding position, which is conducive to penetration. When welding the bottom layer of thick-walled pipe, welding wire is not required, but welding wire is required for the subsequent welding layer.