Multi-layer flux-free material with stepped silicon content and its preparation method and application

Abstract

The invention discloses a multilayer fluxless material with stepped silicon content and a preparation method and an application thereof. The multilayer fluxless material comprises a core layer, a soldering layer and a cover layer which are composited in order, and the silicon mass content of the soldering layer and cover layer are different. The cover layer and the soldering layer contains a silicon material, by using the different differential concentrations of the silicon content of the soldering layer and the cover layer, the soldering liquid flows from high density to low concentration direction, and an oxide-film is effectively broken through. at the same time, Mg with high concentration flows with the silicon material, then is diffused next to the oxide-film, under condition that oxygen content is low, the diffused magnesium and the aluminium alloy oxide-film are subjected to spinel, the generated spinel is easily coiled into the liquid by the soldering liquid (the silicon material), the soldering liquid is fully contacted, capillary and infiltration effects are employed, so that the welding quality of a soldered joint is saturated. a Bi element is added in the cover layer or the soldering layer, and the oxide-film can be firstly broken through.

Description

technical field [0001] The invention relates to a multi-layer aluminum alloy flux-free material for heat transmission and a manufacturing process thereof. Background technique [0002] At present, the development of the heat transfer industry requires the manufacture of high-quality materials and components with the lowest possible final cost. The most commonly used brazing production of heat exchangers is in an atmosphere of nitrogen with as few oxygen impurities as possible. This process, known as Controlled Atmosphere Brazing (“CAB”), also includes Al-K-F based fluxes, such as the Nocolok flux applied, which is achieved by adding brazing flux to decompose, dissolve and remove the oxide film to form wetting and melting. Purpose. [0003] However, post-brazing flux residues are generally considered detrimental to heat exchangers, as they may spread on the brazed aluminum surfaces or clog internal channels, preventing efficient heat transfer with the heat exchanger. The re...

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Problems solved by technology

[0008] However, after the low-melting-point element phases such as Bi, Pb, Sb, and Sn in the solder are melted first, the oxide film is broken and precipitated on the outer surface of the solder, and at the same time, a channel is provided for the diffusion of Mg; when the solder is completely melted, the first melted Bi, Pb, Sb, Sn and other low-melting element phases are pushed to the outermost layer, that is, the first melted Bi, Pb, Sb, Sn and other low-melting element phases form a "cofferdam" around the solder. The formation of the "cofferdam" hinders the spreading of the solder and increases the resistance to the flow of the solder, thus reducing the spreading performance of the solder

Experiments have shown that the greater the amount added, the greater the reduction in spreading performance. None of the above patents can avoid the occurrence of the "cofferdam" phenomenon, and at the same time cannot effectively control the harmful effects of magnesium diffusion.

[0009] In addition, in patents EP 1306207B1 and US2014 / 0315024A1, the covering layers are pure aluminum or aluminum-manganese based. Since the solid-liquidus temperature of the aluminum-silicon layer of the brazing layer is 570-590°C, the pure aluminum of the covering layer is at 650°C, and the solid-liquidus temperature The difference is large. Although there is a difference in the concentration of the silicon material, the silicon material can only erode the pure aluminum little by little. The layer of pure aluminum blocks the insufficient flow of silicon material in the brazing layer. It takes a certain time for the pure aluminum layer to completely dissolve. During this process, the partially diffused magnesium element reacts with the oxide film. When the silicon material completely dissolves the pure aluminum, there is not enough time and power. Roll the oxide film into the brazing solution. If the brazing time is prolonged, the silicon material will corrode the core layer as well as the covering layer. The longer the time, the more the outermost layer will be oxidized, that is, the thicker the oxide film, Welding is very bad

[0010] At present, the most problem encountered by the industry is that the internal welding quality of flux-free brazing is intact, and the external welding is not full. The main reason is: at 600 ° C, the saturated vapor pressure of magnesium alloy volatilization in vacuum is 0.43g / m 3 , can consume 89.58ppm oxygen, take oil cooler brazing as an example, the internal welding quality of oil cooler brazing is intact, but the external welding is not full

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