Flux-Cored Silver Brazing Material for Moisture-Stable Self-Brazing
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Solution Overview
Problem
Current flux-cored silver brazing materials face issues with moisture absorption leading to corrosion of the brazing material outer coat, affecting storage stability and brazing reliability, especially when used with stainless steel and manganese brass, which requires additional costly plating processes to improve brazability.
Innovation Solution
An in-situ synthetic metal-coated flux-cored silver brazing material with a brazing material outer coat composition of silver, copper, zinc, tin, phosphorus, nickel, germanium, and lithium, along with a waterproof protection layer, is developed to enhance storage stability and brazing reliability, eliminating the need for additional plating processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a flux containing boric anhydride, potassium fluoride, potassium bifluoride and other inorganic matter is used in flux-cored brazing material, then the flux can remove oxidation film and protect welded metal against oxidation, but the flux easily absorbs moisture and becomes corrosive, seriously corroding the brazing material outer coat and affecting storage stability
Solution Approach 1:
The patent uses a composite outer coat structure consisting of multiple layers: an inner anti-corrosion layer (containing Al, Si, B, Ti, V, Nb, Ta) that protects against flux corrosion, and an outer brazing layer (containing Ag, Cu, Zn, Sn, Pb, In, Ga) that provides brazing functionality. This composite structure isolates the reactive flux from the outer coat, preventing moisture absorption and corrosion while maintaining brazing reliability.
Solution Approach 2:
The anti-corrosion layer acts as an intermediary barrier between the flux core and the outer environment. It contains harmful substances from the flux through chemical reactions (e.g., Al reacts with moisture to form protective Al2O3) and prevents direct contact between the corrosive flux and the brazing material outer coat, thus protecting the structure while allowing the flux to perform its cleaning function.
2Stability of the object's composition
If a flux having low activity is used to prevent corrosion of the brazing material outer coat, then storage stability is improved, but Cr2O3, TiO2, and MnO2 on surfaces are difficult to remove, seriously affecting brazing reliability
Solution Approach 1:
The outer coat is segmented into functionally distinct layers: the inner anti-corrosion layer (Al, Si, B, Ti, V, Nb, Ta) that provides corrosion resistance and stability, and the outer brazing layer (Ag, Cu, Zn, Sn, Pb, In, Ga) that provides high brazing activity. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
The patent changes the chemical composition parameters of the outer coat by introducing reactive metals (Al, Si, B, Ti, V, Nb, Ta) in the anti-corrosion layer that can chemically interact with flux components. These parameter changes enable the outer coat to resist corrosion from high-activity flux while maintaining storage stability.
3Reliability
If a layer of copper or nickel is plated on the surface of metals that are hard to braze to improve brazability, then brazing reliability is improved, but one procedure is added, operation becomes complex, cost increases, and serious pollution to environment is caused
Solution Approach 1:
The patent merges the anti-corrosion function and the brazing enhancement function into a single integrated outer coat structure. The multi-layer composition (anti-corrosion layer + brazing layer) combines protective and functional properties, eliminating the need for separate plating processes while improving both corrosion resistance and brazing reliability.
Solution Approach 2:
The outer coat serves multiple functions simultaneously: it protects against flux corrosion, prevents moisture absorption, enhances brazing activity, and provides oxidation resistance. This multi-functional design replaces the need for separate copper or nickel plating processes, simplifying the overall manufacturing process while achieving the same brazing improvement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides improved storage stability, high brazing efficiency, and reduced operational costs by preventing corrosion and enhancing the self-brazing capability of the flux-cored silver brazing material, particularly suitable for stainless steel and manganese brass components.
Implementation Method 1
Li can react with Cr2O3 to form a low melting point lithium chromate, so Cr2O3 on a surface of stainless steel can be removed by the Li
Implementation Method 2
a flux of a core of a flux-cored silver brazing material usually contains boric anhydride, potassium fluoride, potassium bifluoride and other inorganic matter, and thus easily absorbs moisture
Implementation Method 3
a flux layer which has absorbed moisture is corrosive, and seriously corrodes a brazing material outer coat wrapping the flux of the core
Data Source
AI summary
A brazing material outer coat and a method for preparing the same, an in-situ synthetic metal-coated flux-cored silver brazing material and a method for preparing the same, a welding method and a joint body, wherein the in-situ synthetic metal-coated flux-cored silver brazing material comprises a flux core and a brazing material outer coat wrapping the flux core, the brazing material outer coat comprises, in percentage by weight: silver Ag 20.0˜36.0%, copper Cu 35.0˜45.0%, zinc Zn 27.0˜37.0%, tin Sn 1.0˜3.0%, phosphorus P 0.1%˜0.5%, nickel Ni 0.5˜2.0%, germanium Ge 0.1˜0.3%, and lithium Li 0.1˜0.3%, the flux core comprises, in percentage by weight: elemental boron micropowder 5.0˜10.0%, sodium borohydride 5.0˜10.0%, potassium fluoroborate 15.0˜30.0%, boric anhydride 25.0˜40.0%, sodium fluoride 10.0˜30.0%, sodium bifluoride 2.0˜4.0%, and copper sulfate 1.0˜5.0%. The in-situ synthetic metal-coated flux-cored silver brazing material in the present disclosure realizes self-reaction in a brazing process to coat a layer of copper film on a surface of a brazed metal, the core of the brazing material has good wettability, good flowability, self-brazing function, and zinc being hard to volatilize, the flux coat has high activity, low hygroscopicity, few carbon residues, good plasticity and toughness, etc. The present disclosure is particularly suitable for brazing pipeline components of stainless steel, manganese brass and so on.