Featuring low weight, relatively high strength, good machinability, aluminum alloys have a greater applicability in all sectors of the economy. High corrosion resistance, thermal conductivity, conductivity, in many cases make them trudnozamenimymi structural materials. In welded structures have proliferated wrought aluminum alloys. Not hardenable by heat treatment (BP, bp 1, AMts, AMgb, etc.), and alloys, hardening by heat treatment (AD31, , 1201, 1420, etc.). Aluminum has the ability to interact with oxygen. The resulting aluminum oxide covers the surface of the metal strong and dense film. Oxidation of aluminum at normal temperature after reaching a maximum thickness of the film virtually stops.
Therefore, the film has a protective effect. The most important characteristic of the film of aluminum oxide is its ability to adsorb gases, especially water vapor. Coefficient of thermal expansion of the film is almost 3 times less than aluminum, so the heating in her cracks. In the presence of the alloy doping Additive composition of the film may change and acquire more complex composition, including oxides of these additives. Such complex films can be more loose, gidroskopichnymi not possess protective properties. Frequently The Florey Institute has said that publicly. The presence of oxide film on the surface of aluminum and its alloys makes the process of welding. With its high melting point (2050 C), the oxide film is not melted during the welding process and metal coating solid shell, makes it difficult formation of a common weld pool.
When welding must be taken to destroy the film and the metal protection against re-oxidation. To remove the oxide film during welding, using the application of flux, and the process of the cathode sputtering. The role of flux in the removal of the film lies in its flushing action. Cathode sputtering due to bombardment of the cathode surface, positively charged ions of the arc. Further, aluminum and alloys are prone to Education in the joints of gas pores and oxide inclusions. Therefore, before welding requires careful surface preparation to remove the old oxide film. Presence on the surface of a solid metal oxide film affect the nature of drop transfer of electrode metal during welding. In the presence of an oxidizing medium size droplets from the electrode reaches a large size and arcing occurs unstable. Starting with a certain current density krupnokapelny transfer metal electrode is replaced melkokapelnym jet. Arc acquires high stability and ability to self-regulation. This is because from a certain value welding current strength coming off a drop from the electrode, prevail over the forces that hold it down. In this regard, the drop breaks away from the electrode before the time to grow to their final dimensions. To eliminate oxide inclusions in the weld metal are recommended various technological methods for mixing the molten pool of metal and fragmentation of oxide films. Aluminum reacts actively with all gases, however, in the presence of atmospheric Oxygen is primarily formed oxide film that prevents further exchange with the environment.