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Aluminum has a low melting point (657°C) with a high coefficient of thermal expansion and significant thermal conductivity - three times higher than that of mild steel. Hot aluminum is very brittle, but the main difficulty in welding it remains its mild oxidation. Aluminum oxide (_Al203) is strong and refractory. It melts at 2050 °C (which is above the boiling point of aluminum) and is poorly resistant to the action of fluxes, because of its chemical neutrality.

Welding.

Aluminum is welded by gas and arc welding, as well as by pressure welding on electric contact welding machines. The most popular gas welding of aluminum with an acetylene-oxygen mixture. Preliminary metal edges are thoroughly cleaned: with sandblasters, steel brushes, scraping or washing in gasoline or in an aqueous solution of caustic soda. After caustic soda, the parts are thoroughly washed under running water to prevent corrosion. When repairing aluminium castings, it is recommended that they are preheated to 300 °C.

Flux

When welding thick-walled aluminum castings, flux is sometimes unnecessary. But then the aluminum oxide must be constantly removed from the surface of the weld pool with a steel wire scraper, and the end of the filler rod is immersed in the weld pool to prevent oxidation. In the usual situation, special fluxes vigorously dissolve aluminum oxide even at low temperatures and greatly facilitate welding. Before the invention of good fluxes welding aluminum because of the complexity almost never practiced. Especially vigorously dissolve aluminum oxide lithium halide compounds. In fluxes for welding aluminum most often introduced lithium chloride or fluoride.

To this day, new, improved fluxes are still being sought. To test the quality of a new flux with a gas torch to melt a small tray on a plate of aluminum covered with a film of oxide with a grayish-matte dull surface. After a pinch of good flux into the bath, its surface is cleaned almost instantly and becomes shiny and silvery, mercury-like. A good flux also cleans the unmelted hot metal around the bath.

Compositions of some of the fluxes used

Flux fabrication and storage

Fluxes and coatings are prepared from chemically pure substances. Fluxes are either thoroughly mixed with simultaneous grinding of the components, e.g. in a mill with a porcelain case and balls, or the components are pre-melted and then thoroughly milled. Flux fusion usually gives better results and less hygroscopicity. Note that aluminum fluxes change their properties when exposed to atmospheric moisture. Therefore, they are stored in tightly corked jars, from which portions are taken only for one shift.

Butt welding

It is usually produced by continuous fusion welding of aluminum on electrically powered machines. At a current value of 15,000 A per 1 ^cm2 of the welded cross-section the melting amount is 5-12 mm and the draft is 1.5-5 mm, depending on the cross-section of the weld. Continuous melting time is 30 to 70 AC periods and settlement time is 2 to 5 current periods. Current is switched off at the beginning of upsetting.

Spot welding

It is significantly hampered by high electrical conductivity of aluminum and its rapid melting during welding (for 0.002-0.005 sec.), so to maintain the value of pressure and contact with the metal you must quickly move the electrode of the machine. Spot welding with accumulated energy is also possible. Condenser spot welding of aluminum is usually used. Electrodes for such welding are taken from copper alloys with high hardness and electrical conductivity. Satisfactory results are given by the alloy E. V. Hinders welding sticking of the copper electrode to aluminum - then you need immediate stripping of the electrode with removal of a thin layer of metal, in order to avoid damaging the surface of the points. It is also necessary to cool the electrodes with running water. Seam welding of aluminum is also possible, and powerful machines with ion breakers are used for this.

Aluminum alloys

In technology, aluminum alloys are widely used with a strength higher than that of pure aluminum, maintaining its low specific gravity (2.7-2.8). Aluminum alloys can be divided into two groups: thermally unhardenable and thermally hardenable alloys. An example of the first group is the alloy AMz, alloyed with 1.3% manganese, with a tensile strength of 13 to 20 ^kg/mm2 depending on the hardening. Such alloys are insensitive to heat treatment, relatively easy to weld, and the weld strength approaches that of the base metal in an annealed state.

Duralumin

Refers to thermally hardenable alloys. It has a number of grades with a tensile strength of 38 to 46 kg! mm2. Welding duralumin is still a challenge. Duralumin is an alloy of aluminum with copper and magnesium forming intermetallic compounds. Their solubility in aluminum depends on temperature. When aluminum is heated above the critical temperature, the compounds fully dissolve in the metal and remain in this form during rapid cooling, i.e. the alloy hardens. During the subsequent aging of the metal, the intermetallic solution disintegrates, giving off particles of compounds in a finely dispersed form, which gives duralumin its mechanical properties of high strength and hardness. During welding, due to local overheating of the metal, the opposite process occurs, causing a loss of mechanical strength. Decrease in strength is not eliminated by further heat treatment.

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The range of aluminum alloy products in the warehouse of Evek GmbH meets the requirements of GOST and international quality standards. The wide range of products of any parameters, exhaustive consulting of our managers, reasonable prices and on-time delivery determine the face of our company. We accept wholesale and retail orders. With wholesale purchases there is a system of discounts.