Welding of aluminium and its alloys
AndLumina has a low melting point (657°C) with a high thermal expansion coefficient and substantial thermal conductivity, three times higher than that of mild steel. Hot aluminium is very fragile, but the main difficulty when welding remains light oxidation. Aluminium oxide (Al203) durable and refractory. It melts at a temperature of 2050 °C (this is above the boiling point of aluminium) and difficult to action of fluxes, because of its chemical neutrality.
Aluminium weld gas and arc welding, and pressure on the electric-welding machines. The most popular gas welding of aluminium acetylenedicarbonic mixture. Pre-edges of the metal are thoroughly cleaned: sandblasting devices, steel brushes, scraping or washing in gasoline or in an aqueous solution of caustic soda. After the caustic soda, the parts washed thoroughly with running water to prevent corrosion. When repairing aluminum castings must be preheated to 300 °C.
When welding thick aluminum castings, it is sometimes possible to do without special flux. But then the alumina should constantly be removed from the surface of the weld pool with a scraper of steel wire, and the end of the welding rod is immersed in the weld puddle to prevent oxidation. In a normal situation, special fluxes vigorously to dissolve the aluminium oxide even at low temperature and significantly facilitate the welding. Before the invention of good flux aluminum welding because of the difficulty almost non-existent. Especially vigorously to dissolve the aluminium oxide halide compounds of lithium. In fluxes for aluminum welding often introduces a chloride or fluoride of lithium.
Still a search for new and better fluxes. To check the quality of the new flux gas burner melt small tray for plate of aluminium coated with a film oxide with grayish-dull matte surface. After a good bit of flux in the bath, its surface is almost instantly cleared and becomes shiny and silvery, like mercury. A good flux also cleans and unmelted hot metal around the bath.
The structures of some of the applied flux
|Filling flux||The number of flux|
|lithium Li CL||15||10||14||9||15||15||-|
The manufacture and storage fluxes
Fluxes and coating are prepared from chemically pure substances. Fluxes or thoroughly mixed with the simultaneous grinding of the components, for example, in the mill with a porcelain body and balls, or in pre-melted components and then thoroughly ground. Fusion fluxes usually gives the best results and lower hygroscopicity. Note that the aluminum flux under the action of atmospheric moisture to change their properties. Therefore, they are stored in tightly sealed jars, from which portions are taken for only one shift.
It is usually produced by continuous melting of aluminum on electrically driven machines. When the value of the current 15000 A 1 cm2 of a welded section the amount of reflow is 5−12 mm, and the sediment of 1.5−5 mm depending on the cross section of the weld. Continuous melting from 30 to 70 periods of the alternating current, and the precipitation time from 2 to 5 periods of the current. The current is switched off at the beginning of the precipitation.
It is substantially difficult due to high conductivity of aluminum and its rapid melting during welding (0,002−0,005 sec.) therefore, to maintain pressure and contact with metal you need a rapid displacement of the electrode of the machine. It is also possible spot welding of stored energy. Usually used condenser spot welding of aluminium. Electrodes for such welding take copper alloy with high hardness and electrical conductivity. Satisfactory results are obtained by the alloy E. V. Complicates the welding adhesion of the copper electrode to the aluminum — then require immediate cleaning of the electrode with the removal of a thin layer of metal, to prevent damage to the surface points. Also requires cooling of the electrodes under running water. Possible and seam welding of aluminium, this is done using powerful machines with ion breakers.
Alloys of aluminium
In the technique widely used aluminum alloy with strength higher than the strength of pure aluminum that retains its low specific weight (2.7−2.8 m). Aluminum alloys can be divided into two groups: non-treatable and heat-treatable alloys. An example from the first group can serve as the AMC alloy, alloyed 1.3% manganese, a tensile strength of from 13 to 20 kg/mm2 depending on strain-hardening. Such alloys are not sensitive to heat treatment, it is relatively easy to weld, and the weld strength approaches the base metal in the annealed condition.
Made of anodized aluminum
Applies to heat-treatable alloys. It has a number of grades with a tensile strength of from 38 to 46 kg! mm2. Welding of aluminum is still the problem. Duralumin is an alloy of aluminium with copper and magnesium forming an intermetallic compound. Their solubility in aluminum depends on temperature. When heating the aluminum above the critical temperature, the compounds are completely dissolved in the metal and will stay in this form when they are rapidly cooled, i.e., is hardening of the alloy. During subsequent aging (aging metal) intermetallic solution decomposes, releasing particles of the compounds in finely divided form, which gives the aluminum its mechanical advantages — high strength and hardness. During welding due to local overheating of the metal, the process is reversed, causing the loss of mechanical strength. The strength reduction is not eliminated by a subsequent heat treatment.
To buy, price
The range of products from aluminum alloys in the warehouse of the company «Electrocentury-steel» corresponds to GOST requirements and international quality standards. A wide selection of products of any parameters, comprehensive advice from our managers, reasonable prices and timely delivery define the face of our company. We accept wholesale and retail orders. When wholesale purchases of discount system.
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