Understanding Melting Points When Choosing the Right Silver Brazing Alloy for Your Application

When it comes to choosing the right silver brazing alloy for your application, understanding melting points is crucial. The melting point of the alloy plays a significant role in determining how suitable it will be for your specific needs. In this blog post, we delve into the world of melting points and hopefully provide you with valuable insights to make an informed decision.

The Solidus and Liquidus Temperatures

Most silver alloys used for brazing have more than one melting point. Let's take the example of alloy 455, which melts at a range of 630-660 degrees Celsius. Within this range, there are two essential temperatures to consider:

Solidus Temperature

The lower temperature (630 in the case of 455) is known as the ‘Solidus’ and it represents the highest temperature where the alloy remains partially solid.

Liquidus Temperature

The higher temperature (660 in 455) is known as the ‘Liquidus’ and it represents the lowest temperature at which the alloy becomes fully molten.

The difference between these two temperatures is known as the "melting range."

Working Temperature

Generally, brazed joints are produced at a temperature below the Liquidus as the alloy becomes fluid enough to flow into the joint before it is fully molten. This is referred to as the "working temperature".

Eutectic Alloys

Some brazing and soldering alloys have only a single melting point. These are known as "eutectic" alloys, for example 2207, which melts at 221 degrees Celsius. Eutectic alloys are exceptionally fluid and should only be used in situations with very tight joint gaps.

Considerations When Choosing Melting Temperature

Choosing the right melting temperature is critical for the success of your brazing or soldering project. Here are some key considerations:

1. Impact on Parent Metals

It's essential to select an alloy with a melting point significantly below that of the parts being joined. Working at too high a temperature can affect the parent metals such as annealing or discolouration, or in extreme circumstances, melting the parent metals.

2. Heating Equipment Capability

Your heating equipment must be capable of heating the parent metals above the melting range of the alloy you're using, preferably quickly. If you're looking for suitable heating equipment, check out our Sievert Heating Range available at CuP Alloys.

3. Joint Gap Control

Alloys with a narrow melting range, such as alloy 455 with a range of 30 degrees, should only be used in situations with close and well-controlled joint gaps. Using these alloys in wider gaps might require excessive amounts of alloy, resulting in a costly joint. If the joint gap is wide and/or cannot be controlled, consider a wider melting range alloy such as 438 (650-720C)

4. Large Components and Heating Speed

For large components or situations where your heating equipment may not heat the components quickly enough, use an alloy with as low a melting point. During the heating cycle certain elements of the brazing alloy, eg silver, tin and zinc, will begin to melt first flowing into the gap. This can lead to the higher melting elements eg copper remaining in a solid state reducing further capillary flow and potentially producing a weak joint. This is a phenomenon called ‘Liquation’ To avoid this, opt for alloys with melting ranges of less than 70 degrees Celsius.

FAQs

What is the significance of the melting range in silver brazing alloys?

The melting range, which includes the solidus and liquidus temperatures, determines at what temperature the alloy becomes molten and can flow into joints. It helps you choose the right alloy for your specific application.

Can I use an alloy with a melting point close to the parent metals?

It's not advisable. Using an alloy with a melting point too close to that of the parent metals can risk melting the parent metals themselves, which is usually undesirable.

What are eutectic alloys, and when should I use them?

Eutectic alloys have a single melting point and are very fluid. They are suitable for situations with very tight joint gaps, where quick and complete melting is essential.

How do I know if my heating equipment is suitable for my brazing project?

Ensure that your heating equipment is capable of heating the parent metals above the melting range of the chosen alloy. If in doubt, contact CuP Alloys.

What should I consider when dealing with joint gaps?

For narrow and well-controlled joint gaps, you can use alloys with narrow melting ranges. In wider gaps, consider alloys with longer melting ranges to avoid excessive alloy usage.

How does melting temperature affect capillary flow in brazing?

Inadequate heating can leave higher melting components in a solid state, increasing the liquidus temperature and affecting capillary flow. To prevent this, choose alloys with melting ranges of less than 70 degrees Celsius.

Are there other factors besides melting points to consider when selecting a brazing alloy?

Yes, factors like material compatibility, corrosion resistance, and the intended application temperature should also influence your choice of brazing alloy.

How can CuP Alloys assist with my brazing and soldering needs?

CuP Alloys provides a comprehensive range of high-quality brazing products, technical support, and efficient delivery services. Feel free to contact us for further information and expert guidance on your brazing and soldering projects.

Contact us for Further Information

Choosing the right silver brazing alloy can be a complex decision, but understanding melting points is a fundamental step in the process. If you have more questions about melting points or any other aspect of brazing and soldering, please don't hesitate to contact us. We're here to provide you with the information and expertise you need for successful brazing projects.