The thesis is devoted to creation of fluoride reactive fluxes, development of technology of brazing of aluminum thin - walled (from 0,1 mm and more) multielement designs with difficult closed profiles in the high purity argon atmosphere.
The processes of high-temperature reactive-flux brazing of aluminum alloys with low magnesium content using reactive fluxes of the salt system K, Al, Si/F, which contribute to the full passage of aluminothermic reduction of silicon from the flux KF-AlF3-(K2SiF6+AlF3) and, accordingly, increases the mass fraction of newly formed aluminum-silicon alloy in the narrow gap, which provides the formation of of integral joints with high strength at the level of the base material and a significant filling of brazing seam.
On the contact surface of aluminum at a temperature above the formation of a double eutectic Al-Si, two processes occur: the reduction of silicon from the composition of potassium silicon fluoride and contact-reactive melting of silicon with aluminum. As a result of this interaction, a metal layer of the Al-Si system is formed, the composition of which is close to the eutectic, which is confirmed by the results of micro-X-ray spectral analysis.
The microstructure of the crystallized metal layer Al-Si contains grains of solid solution based on aluminum, supereutectic component with a concentration of silicon (wt.%): 15,48–17.18, as well as separate discrete inclusions of the plate phase Fe11Si25Al64.
The structural features of the formation of brazing joints with filler metal and without the addition of filler metal are determined. When brazing without the addition of filler metal (only with flux), a structure is formed, which is characteristic of the penetration of
the liquid phase of the low-melting alloy Al-Si along the grain boundaries of the parent metal.
It is determined that the potential difference between the aluminum substrate and the KF-AlF3-(K2SiF6+AlF3) flux in the Al–filler metal(Al-12Si)–flux system does not exceed 0.05 V, which is characterized by the lowest electrochemical heterogeneity.
The results of complex mechanical tests under heavy loads (in particular, vibration in the frequency range from 20 to 2000 Hz, shocks with acceleration up to 35 g) showed high strength and integrity of the brazed thin-walled structure.
Based on the research results, non-hygroscopic fluoride fluxes were created, a technological process of furnace brazing of thin-walled aluminum waveguide structures in a controlled gaseous medium was developed.
