Three-Layer Cu-P-Sn Brazing Wire for Thin High-Sn Joining
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Solution Overview
Problem
Current copper-phosphorus-silver brazing filler metals used in the air-conditioning and refrigeration industries are costly due to silver content, and existing copper-phosphorus-tin brazing wires face challenges in achieving small diameters and high Sn content without forming defects like pores and inclusions, which degrade mechanical properties.
Innovation Solution
A copper-phosphorus-tin brazing wire with a three-layer structure, comprising a Cu inner layer, a Cu-14P alloy middle layer, and a Sn outer layer, with a mass ratio of Cu:P:Sn=86:7:7, and a preparation method involving heating and smelting these components to achieve a wire diameter of 0.1-0.5 mm, ensuring better flow performance and reduced melting temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If Sn content is increased to reduce melting temperature and save silver, then cost is reduced and melting temperature decreases, but CuSn brittle phase forms and processing performance deteriorates
Solution Approach 1:
The brazing wire is divided into three distinct layers: inner Cu layer, middle Cu-14P alloy layer, and outer Sn layer. This segmentation allows each layer to perform its specific function - the Cu core provides structural integrity, the Cu-14P layer controls melting temperature and prevents brittle phase formation, and the outer Sn layer provides low melting point and good flow performance, thereby resolving the contradiction between high Sn content and processing performance.
Solution Approach 2:
Different regions of the brazing wire have different compositions and properties tailored to specific functions. The inner Cu layer has high strength, the middle Cu-14P layer has controlled eutectic composition for optimal melting behavior, and the outer Sn layer has low melting point and excellent wetting properties. This local quality differentiation allows the wire to achieve both low melting temperature and good processing performance simultaneously.
2Manufacturing precision
If conventional preparation methods are used for high Sn content brazing wire, then manufacturing simplicity is maintained, but wire diameter below 0.5 mm cannot be obtained
Solution Approach 1:
The preparation process is segmented into distinct stages: drawing the Cu core wire to precise diameter, plating the Cu-14P alloy layer uniformly on the core, and finally coating the outer Sn layer. This segmentation of the manufacturing process enables precise control of wire diameter and layer thickness, achieving wire diameters below 0.5 mm while maintaining manufacturing feasibility.
Solution Approach 2:
The Cu core wire is prepared first with precise diameter control through drawing processes, then the Cu-14P alloy layer is plated onto the pre-prepared core, and finally the Sn layer is applied. This preliminary preparation of the core structure before adding functional layers enables precise dimensional control and simplifies the overall manufacturing process for thin-diameter wires.
3Reliability
If copper-phosphorus-silver brazing filler metal is used, then brazing capability is maintained, but defects such as pores and inclusions form and mechanical properties decrease
Solution Approach 1:
The harmful Ag element is extracted from the brazing filler metal composition and replaced with a three-layer Cu-Cu-14P-Sn structure. This extraction eliminates the tendency to form pores and inclusions associated with Ag-based filler metals, while the new composition maintains excellent brazing capability through the low melting point eutectic reaction of Cu-14P-Sn system, thereby improving reliability and reducing defects simultaneously.
Solution Approach 2:
The brazing wire is designed as a composite material with three distinct layers having different properties. The Cu-Cu-14P-Sn composite structure leverages the advantages of each component: Cu provides strength and ductility, Cu-14P provides controlled melting behavior and prevents brittle phase formation, and Sn provides low melting point and excellent wetting. This composite approach eliminates defects while maintaining superior brazing quality.
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 results in a brazing wire with improved mechanical properties, reduced defects, and stable brazing quality, overcoming the limitations of traditional methods by achieving a lower melting temperature and better flow performance while maintaining high Sn content and small wire diameter.
Implementation Method 1
the middle layer is Cu-14P alloy... the melting temperature of the brazing filler metal is lower (which can reach 645-660℃), and the flow performance thereof is better
Implementation Method 2
heating and smelting these components to achieve a wire diameter of 0.1-0.5 mm
Data Source
AI summary
The present disclosure provides a copper-phosphorus-tin brazing wire and a preparation method thereof, relates to the technical field of brazing materials. The copper-phosphorus-tin brazing wire is of a three-layer structure, the inner layer is Cu, the middle layer is Cu-14P alloy, and the outer layer is Sn, wherein the mass percentage of Sn is over 7%. The present disclosure solves the technical problems in the prior art that the copper-phosphorus-silver brazing filler metal is prone to produce defects such as pores and inclusions when brazing copper alloys, which leads to the decline of the mechanical properties of the joint, and simultaneously provides the preparation method of the copper-phosphorus-tin brazing wire, such that the technical problem that it is difficult to obtain copper-phosphorus-tin brazing wire with a wire diameter below 0.5 mm under the condition of high Sn content is solved.