Brazing and soldering materials temperatures
Soldering and brazing are metal joining processes that use a filler material with a melting point lower than that of the base metals. Soldering typically operates below 450 °C / 842 °F, while brazing operates above that threshold, reaching temperatures above 900 °C / 1652 °F in certain alloys. Correct selection of the filler material, flux, and working temperature determines the mechanical strength, corrosion resistance, and suitability of the joint for each industrial application.
Operational parameters
Section titled “Operational parameters”Working temperature is the critical parameter that differentiates the two processes. In soldering, low-melting-point alloys are used, such as tin‑lead or tin‑silver‑copper, with working ranges between 180 °C / 356 °F and 450 °C / 842 °F. In brazing, alloys of copper, silver, nickel, or aluminum are used, melting from approximately 450 °C / 842 °F up to over 1100 °C / 2012 °F. Recommended joint clearance varies between 0.03 mm / 0.0012 in and 0.08 mm / 0.0031 in to ensure good capillary action, although in certain brazing operations clearances up to 0.6 mm / 0.024 in are acceptable.
| Filler material | Typical composition | Melting range | Type | Typical base metals |
|---|---|---|---|---|
| 50‑50 solder | 50% Sn, 50% Pb | 183 – 215 °C / 361 – 419 °F | Soldering | Copper, brass, mild steel |
| 60‑40 solder | 60% Sn, 40% Pb | 183 – 190 °C / 361 – 374 °F | Soldering | Electronics, copper, brass |
| Tin‑silver (Sn96Ag4) | 96% Sn, 4% Ag | 221 – 230 °C / 430 – 446 °F | Soldering | Copper, stainless steel (with active flux) |
| Yellow brass | Cu‑Zn (~70% Cu, 30% Zn) | 905 – 932 °C / 1661 – 1710 °F | Brazing | Steel, copper, brass |
| Admiralty brass | Cu‑Zn‑Sn | 900 – 940 °C / 1652 – 1724 °F | Brazing | Steel, copper, bronze |
| Aluminum bronze | Cu‑Al ( ~5‑11% Al) | 1027 – 1038 °C / 1881 – 1900 °F | Brazing | Stainless steel, carbon steel |
| Copper | Pure Cu | ~1084 °C / 1983 °F | Brazing | Steel, tungsten carbide |
| Pure silver | Pure Ag | ~961 °C / 1762 °F | Brazing | Copper, brass, stainless steel |
| Silver alloy (BAg‑1) | Ag‑Cu‑Zn‑Cd | 607 – 618 °C / 1125 – 1144 °F | Brazing | Copper, brass, steels |
| Aluminum‑silicon (4047) | Al‑12% Si | 577 – 582 °C / 1071 – 1080 °F | Brazing | Aluminum and its alloys |
Applicable materials
Section titled “Applicable materials”The base metals most commonly joined by soldering and brazing include:
- Copper and its alloys: are easily soldered with tin‑lead and silver alloys, and can be brazed with brass, copper‑phosphorus, or silver alloys.
- Carbon and low‑alloy steel: accept both soldering and brazing; the latter is usually performed with brass, aluminum bronze, or silver alloys.
- Stainless steel: requires active fluxes and, in brazing, silver or nickel alloys to avoid embrittlement.
- Aluminum and its alloys: are only brazed with aluminum‑silicon alloys, since conventional solders do not wet properly.
- Cast iron and nickel alloys: are brazed with nickel or copper fillers, typically with controlled preheating.
Advantages and limitations
Section titled “Advantages and limitations”Advantages
- The base metal is not melted, allowing tighter dimensional tolerances and less thermal distortion than in fusion welding.
- Ease of joining dissimilar metals (copper‑steel, steel‑carbide, aluminum‑copper, etc.).
- Clean joints that do not require secondary grinding operations.
- Adaptable to mass production and automation.
- In brazing, high mechanical strengths are obtained, often exceeding those of the filler material.
Limitations
- The strength of a soldered joint is limited; it does not exceed that of the filler material and is lower than that of a welded joint.
- Brazed joints lose strength at high service temperatures close to the melting point of the filler.
- Thorough cleaning of the surfaces is essential to achieve proper wetting and capillary action.
- Some filler alloys require aggressive fluxes that must be completely removed to prevent subsequent corrosion.
- The color difference between the filler and the base metal can be an aesthetic drawback.
Selection guide
Section titled “Selection guide”Selection of the filler material is based on:
- Service temperature of the joint: select a filler whose melting point is at least 50 °C / 90 °F above the maximum working temperature.
- Metallurgical compatibility: avoid the formation of brittle phases; for example, do not use fillers with cadmium on stainless steels at high temperatures.
- Type of heating: the method (torch, furnace, induction) determines the required melting range and fluidity.
- Mechanical and corrosion requirements: joints for marine environments benefit from fillers with silver or tin‑silver.
- Joint clearance: alloys with a wide melting range (pasty) tolerate larger clearances.
- Applicable regulations: for plumbing, food, or gas applications, lead‑free fillers must be used.
| Criterion | Recommendation for soldering | Recommendation for brazing |
|---|---|---|
| Service temperature < 100 °C / 212 °F | Sn‑Pb, Sn‑Ag‑Cu | Not applicable |
| Service temperature 100‑200 °C / 212‑392 °F | Sn‑Ag (up to 180 °C / 356 °F) | Zn‑Al alloys |
| Service temperature > 200 °C / 392 °F | Not recommended | Cu‑P, Ag, brass alloys |
| Copper‑copper joint | Sn‑Pb or Sn‑Ag | Cu‑P (self‑fluxing on copper) |
| Aluminum joint | Not feasible | Al‑Si (4047) |
| High mechanical strength | Limited | Silver alloys (BAg) or aluminum bronze |
| Corrosive environments | Sn‑Ag | Ag‑Cu‑Zn, aluminum bronze |
Soldering and brazing processes
Section titled “Soldering and brazing processes”Soldering: the filler material is melted with a soldering iron, gas torch, or by immersion at temperatures below 450 °C / 842 °F. The most common fluxes are based on rosin (electronics) or zinc chloride (plumbing). Wetting occurs by capillary action if the clearance is appropriate and the surfaces are clean.
Brazing: the filler is heated above 450 °C / 842 °F using an oxyacetylene torch, induction, furnace with controlled atmosphere, or electrical resistance. Fluxes based on borax and fluorides are used to remove oxides. Protective atmosphere (nitrogen, hydrogen, vacuum) can replace the flux and avoid subsequent cleaning. Thermal cycles must be controlled to minimize interaction between the filler and the base metal.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the typical working temperature of soldering?
Section titled “What is the typical working temperature of soldering?”Soldering is generally performed between 180 °C / 356 °F and 450 °C / 842 °F, depending on the filler alloy.
At what temperature does 50‑50 tin‑lead solder melt?
Section titled “At what temperature does 50‑50 tin‑lead solder melt?”The 50‑50 Sn‑Pb alloy melts in a range of 183 °C / 361 °F to 215 °C / 419 °F, being fully liquid at 215 °C / 419 °F.
What is the melting temperature of yellow brass used in brazing?
Section titled “What is the melting temperature of yellow brass used in brazing?”Yellow brass melts between 905 °C / 1661 °F and 932 °C / 1710 °F, making it suitable for joining steels and copper.
What minimum temperature must a process have to be considered brazing?
Section titled “What minimum temperature must a process have to be considered brazing?”It is considered brazing when the temperature of the filler material exceeds 450 °C / 842 °F.
At what temperature does the aluminum‑silicon 4047 alloy melt?
Section titled “At what temperature does the aluminum‑silicon 4047 alloy melt?”The Al‑Si 4047 alloy has a very narrow melting range, from 577 °C / 1071 °F to 582 °C / 1080 °F.
What is the melting point of pure copper used as filler in brazing?
Section titled “What is the melting point of pure copper used as filler in brazing?”Pure copper melts at approximately 1084 °C / 1983 °F, and is used for joints operating at high temperature.
References
Section titled “References”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html
- manufacturingguide.com: https://www.manufacturingguide.com/en/vertikal-cnc-svarvning