All-Russian Institute of Aviation Materials at the National Research Centre Kurchatov Institute, Moscow, Russia:

N. D. Shchetinina, Engineer
I. Benarieb, Engineer, e-mail: benar1294@gmail.com
N. V. Dynin, Head of Department
S. V. Sbitneva, Senior Researcher, Candidate of Technical Sciences

The problem of enhancing the quality of brazed joints in plate-fin heat exchangers made of aluminium alloys is of relevance for designing new aircraft components. This paper presents a brief literature review that looks at the diffusion interaction of liquid solder with the base alloy when brazing aluminium alloys. The said phenomenon presents an important problem as it affects the brazability leading to erosion and compromised properties of the brazed joint. With the help of scanning and transmission electron microscopy, the authors examined the structural and phase state of cold-rolled sheets (H₂ state) made of a new wrought Al – Mn – Mg (of AlMn type) alloy clad with an Al – Si – Mg (silumin type) alloy after high-temperature vacuum brazing. It was found that during brazing the subgrain base alloy structure becomes recrystallized while the manganese dispersoids of the α-phase Al₁₅(Mn,Cr,Fe)₅Si₂ retain their size, quantity and distribution pattern in the aluminium matrix. The authors examined the effect of the temperature/time parameters of a simulation brazing operation on the size of the erosion layer and mechanical properties of the sheets. The high-temperature heating that simulates the brazing process leads to a noticeable decrease in the ultimate and yield strengths and affects elongation as a result of lower strain hardening and the embrittling effect of the erosion layer. The paper demonstrates that the application of certain brazing regimes and preannealing of sheets in their initial state can help inhibit degradation of the material properties after brazing and thus make the erosion layer smaller. The paper outlines factors to be taken into account in order to achieve an enhanced brazing quality: the chemical composition of the base alloy and the concentration of iron and silicon; the temperature/time parameters of the brazing process, especially the soaking time; the initial structural state of the sheet that determines the way silicon gets diffused into the core material.
This research was carried out using the facilities of the Climatic Tests Shared Knowledge Centre at the All-Russian Institute of Aviation Materials as part of the following research area: Light, high-strength, corrosion resistant weldable alloys and steels, including alloys and steels with high fracture toughness (Strategic Areas in the Development of Materials and Processing Techniques for the Period till 2030). 

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