Effective protection measures for aluminum alloy pipeline welding

Aluminum alloy pipe refers to a hollow metal pipe material made of pure aluminum or aluminum alloy after extrusion along its longitudinal length. Can have one or more closed through holes, wall thickness, uniform cross section, straight or roll delivery. Widely used in automobile, ship, aerospace, aviation, electrical appliances, agriculture, mechanical and electrical, household and other industries. With ordinary carbon steel tube as the foundation, lined with excellent chemical thermoplastic, through cold drawing composite or rolling plastic molding, it has both the mechanical properties of steel tube, plastic pipe corrosion resistance, slow scaling, not easy to grow microorganisms, is the transport of acid, alkali, salt, corrosive gas and other media ideal pipeline.

Aluminum alloy is widely used in all kinds of welded structural products because of its light weight, high strength, good corrosion resistance, non-magnetic, good formability and low temperature performance. In particular, the path of thin - walled pipe welding more difficult to master. Therefore, it is necessary to solve the welding defects of aluminum and aluminum alloy in the construction process.

Aluminum alloy pipeline although this layer of aluminum oxide film is dense, can prevent the continued oxidation of the metal, beneficial to natural corrosion, but it brought difficulties to welding, because the melting point of aluminum oxide (2050℃) far beyond the melting point of aluminum (600℃ or so), the specific gravity is about 1.4 times that of aluminum. In the welding process, will hinder the fusion between the metal, easy to form slag inclusion, and alumina film also adsorbed more moisture, welding will promote the formation of weld pores. The thermal conductivity of aluminum is very large. Under the same welding process, the cooling speed of aluminum is 4 ~ 7 times that of steel, which accelerates the crystallization of metal. During the rapid cooling process of welding pool, the solubility of hydrogen drops sharply, and a large amount of susaturated gas is precipitated at this time, and hydrogen is too late to precipitate and form pores in weld metal.

Therefore, when welding aluminum, the tendency of porosity is very big. When aluminum and aluminum alloys change from solid to liquid state. Because there is no obvious color change, it is not easy to judge the temperature of the molten pool. When welding, the temperature is often too high to be detected and cause burning through or serious collapse.

The groove and welding wire cleaned by aluminum alloy pipeline shall not be stained again before welding. If there is no effective protective measures, welding shall be performed within 8 hours. Otherwise, clean up again. When the pipeline group is aligned, the inner wall should be even without burr or particles, and the amount of wrong side should be in line with b≤0.5mm. It has the external characteristic of steep drop and sufficient capacitance. In addition, it has stable parameters, flexible regulation and safe and reliable performance. It should also have devices for arc starting, arc stabilizing and eliminating dc components. The current and voltmeter on the welding machine should be qualified by the measurement department.