The surface of aluminium and its alloys because of the easy oxidizability covered durable oxide film that impedes soldering. An additional complication is that the soldering points are prone to corrosion. Soldering can be facilitated if a galvanic way in advance precipitate on aluminum copper or Nickel, soldering etched with sulfuric acid, sodium hydroxide solution, followed by rinsing in water, and then subjected to Nickel plating or copper plating in the plating bath. Surface covered by a film of Nickel or copper, soldered conventional soft solders. But the method of electroplating a complex, time-consuming and quite expensive. Usually just smooth out the edges before soldering and use special solders for soldering aluminium — often technically pure zinc. When soldering, by grinding it gives a seam strength of about 9 kg/mm2, however, these compounds are rapidly korrodiruet. The solders of the first and second give a tensile strength of not lower than 10 kg/mm2. The third solder has a special strength and a considerable elongation; the limit of strength of about 8 kg/mm2. The fourth solder is prone to fragility, but provides the seam strength up to 20 kg/mm2. Note that the strength of the solder joint increases with increasing the melting temperature of the solder.
|Percentage composition of solder for aluminium and its alloys|
|-||-||-||Basis||5,2−6,5||25−29||The brazing alloy, TM =525°; the proposed S. N. Limanowa|
The composition of flux and solder
For the flux use rosin, stearine, icing sugar. Pre-solder rubbed on the surface with a brush or scraper. For overlapping joints is sometimes used as a solder, powdered zinc chloride. Stripped for soldering surface is poured a powder of dry zinc chloride and heated. Zinc chloride melts with the release of acrid smoke. As a result of exchange reactions of the aluminum unites with the chlorine to evaporate, and the molten zinc alloyed with aluminum, penetrating into the surface layer. Thus, the surface of aluminum oblizyvaetsya zinc, and the parts connected by the alloy of zinc and aluminum.
Heat bonded overlap tinned parts gives them a strong connection, corrosion resistant. More durable soldering requires more high-melting solders and special fluxes. For example, a special solder for aluminum is 25−30% copper, 4.7% of silicon and the rest aluminum. Solder melts at 525 °C and is used in conjunction with a flux of lithium chloride 25−30%; potassium fluoride 8−12%; zinc chloride 8−15% and potassium chloride — the rest. The flux melts at 450 °C. Such solders and flux provide a solid soldering of aluminium.
To buy, price
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