How to Understand the Selection of Brazing Materials: A Comprehensive Guide
Release date: 2017-10-26 Source: Foreign station Sharing: 
Choosing the right brazing filler metal is crucial for achieving high-quality brazed joints. The selection process should consider the compatibility between the filler and base metals, the operating conditions of the parts, available equipment, and cost-effectiveness.
**Classification of Solder**
1. Based on melting temperature:
(a) Low-melting-point solder (below 450°C): such as tin-based, lead-based, or zinc-based alloys.
(b) High-melting-point solder (above 450°C): also known as refractory brazing filler metals, including aluminum-based, copper-based, silver-based, nickel-based, and gold-based alloys.
2. Based on main alloying elements:
Solders can be categorized as silver-based, copper-based, tin-based, lead-based, or aluminum-based depending on their primary alloy components.
3. Based on shape:
Solders come in various forms such as wire, rod, sheet, foil, powder, or special shapes like rings and pastes.
4. Based on flux requirements:
Some solders are self-fluxing, meaning they don’t require additional flux. These typically contain elements like phosphorus or lithium. Others require added flux to ensure proper wetting and bonding.
**Brazing Characteristics**
Before choosing a solder, it's essential to understand its physical properties, melting behavior, and formability. The composition of the solder determines how well it wets the base material and fills the joint without forming harmful compounds.
The melting behavior of a solder is influenced by its metallurgical composition. For example, eutectic alloys have a single melting point, while non-eutectic alloys melt over a range. Understanding this helps in selecting the appropriate solder for specific applications.
**Common Solder Forms**
Solders are available in various forms—wire, sheet, ring, powder, paste, foil, preform, etc.—depending on the application, joint design, and production efficiency needs.
**Brazing Material Selection Method**
When selecting a solder, factors such as base metal compatibility, joint performance, melting point, wetting ability, diffusion effect, and economic considerations should all be taken into account.
Key considerations include:
- Matching the solder’s melting point with the base metal to avoid damage during brazing.
- Ensuring good wetting and filling of the joint gap.
- Ensuring strong bonding through diffusion between the filler and base materials.
- Minimizing alloy element loss during the brazing process.
- Meeting mechanical, thermal, and chemical performance requirements.
- Considering cost and availability of the material.
- Ensuring the solder can be shaped easily for different applications.
**Working Conditions and Application Requirements**
The choice of solder depends on the operating environment, such as temperature, load, and corrosion resistance. For example, high-temperature applications may require nickel-based or cobalt-based solders, while corrosion-resistant joints often use gold or palladium-based alloys.
**Conclusion**
Selecting the right brazing material is a critical step in ensuring the quality and durability of brazed joints. It requires careful consideration of multiple factors, including material compatibility, application requirements, and cost-effectiveness. By following best practices and understanding the characteristics of different solder types, engineers and technicians can make informed decisions that lead to successful brazing outcomes.
This article was written by Guangzhou Xianyi Electronic Technology Co., Ltd.
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