Frequently Asked Questions


Q. What is Brazing? Welding? Metallizing?

A: Brazing is a process for joining similar or dissimilar metals using a filler metal that typically includes a base of copper combined with silver, nickel, zinc or phosphorus. Brazing covers a temperature range of 900°F - 2200°F (470°C - 1190°C). Brazing differs from welding in that brazing does not melt the base metals, therefore brazing temperatures are lower than the melting points of the base metals. For the same reason, brazing is a superior choice in joining dissimilar metals. Brazed joints are strong. A properly-made joint (like a welded joint) will in many cases be as strong or stronger than the based metals being joined.

Typically brazing is employed in manufacturing compressors, diesel engine circulation tubes, mining tools, plumbing fixtures, jewelry, musical instruments, refrigerators, condensers, and automotive applications.

Welding is a process for joining similar metals. Welding joins metals by melting and fusing: 1) the base metals being joined and 2) the filler metal applied. Welding employs pinpointed, localized heat input. Most welding involves ferrous-based metals such as steel and stainless steel. Welding covers a temperature range of 1500°F - 3000°F (800°C - 1635°C). Weld joints are usually stronger or as strong as the base metals being joined.

Metallizing (a.k.a. Thermal Spraying) is a process to apply wear and corrosion resistant coatings for component protection and reclamation. Key industrial sectors include aerospace, automotive, power generation, petrochemical, biomedical, dielectric and offshore drilling.



Q. How do I TIG weld alloy C91000?

A: Alloy C91000 is a high tin bronze. For TIG welding, you can use our Phos Bronze A or our Silicon Bronze rod. Phos Bronze A gives better color match. Silicon Bronze gives stronger welds. The TIG welding temperature for both of these filler metals is a little higher than the melting point of the C91000 (1505°F solidus, 1760°F liquidus). Because of this temperature concern, and depending on the thickness of the welded part, you may want to consider brazing. To braze C91000, you may use our PhosCopper 0 alloy.



Q. How many rods per lb. ?

A: The number of rods per pound varies with the alloy and with the diameter.
Here are a few commonly used alloys and diameters.

Diameter (inches) ALUM 4043 BARE #681 FC #681
1/16 96 32 23
3/32 44 14 13
1/8 27 8 7


Q. Brazing Concepts: Solidus, Liquidus and Brazing Range

A: When brazing, the terms melting point and freezing point are not properly used, unless you are dealing with an unalloyed metal. Almost all brazing filler metals are alloys (combinations of elements). You cannot simply guess the melting point of an alloy by figuring the weighted average of the melting points of its elements. Usually, alloys are mixtures that melt little by little through a range of temperatures. A metallurgist makes a distinction between a pure metal's melting point and a brazing filler metal's melting range.

Solidus - The temperature at which an alloy begins to melt.

Liquidus - The temperature above which an alloy is completely molten.

Eutectic Point - An alloy is an “Eutectic composition” if it has a specific melting point like that of a pure metal. The eutectic alloy's melting range is small; solidus and liquidus are almost equal. The melting point in this case is called the “eutectic point.”

Brazing Range - To ensure a free flowing action, brazing usually requires temperatures above the liquidus. But, for example when brazing joints with a wide gap, you may need a more pasty, sluggish brazing filler metal that will not flow all over the joint. Sometimes, then, the low end of the brazing range for certain brazing filler metals is below the liquidus.



Q: Why are my TIG welds cracking? Why are some and not all of my welds cracking?

A: The aluminum / magnesium / silicon base alloys (6xxx series aluminum) are highly crack sensitive because they contain approximately 1% Magnesium Silicide (Mg2Si), which falls close to the peak of the solidification crack sensitivity curve.

The Mg2Si content of these materials is the primary reason that there are no 6xxx series filler alloys made. The cracking tendency of these alloys is lowered to acceptable levels during arc welding by the dilution of the weld pool with excess magnesium (by use of the 5xxx series Al-Mg filler alloys) or excess silicon (by use of the 4xxx series Al-Si filler alloys).

When we TIG (GTAW) weld on thin material, it is often possible to produce a weld, particularly on corner joints, by melting both edges of the base material together without adding filler material. In the majority of arc welding applications with this base material, we must add filler material if we want to have consistently crack free welds. A possible exception would be counteracting the cracking mechanism by maintaining a compressive force on the parts during the welding operation, which requires specialized fabrication techniques and considerations. This method is seldom used.

It is possible that the welds that are not cracking are those that have had filler material added during welding. We recommend adding filler alloy to all welds during welding in order to reduce crack sensitivity. Consideration should also be given when evaluating the cause of cracking to any differences in welds associated with weld size, and variations in tensile stresses introduced by shrinkage, joint expansion, or externally applied loads.



Q: What is the tensile strength of brazed joints?

A: It all depends. No manufacturer lists the tensile strength of their brazing alloys. This is not to make life difficult for the ultimate consumer. It is because people tend to place too much emphasis on any number that might be published. Design engineers sometimes base designs on a number that is not appropriate for the ultimate use.

In fact, the strength of a brazed joint depends more on the design and the brazing technique rather than on the filler metal used.

Furthermore, tensile strength numbers that Aufhauser has measured apply to material in the wrought state. When the filler metal is used in brazing, it is effectively recast. Recast metal has different properties from the wrought metal.

Empirical testing of various brazed joints has shown that the PSI of the alloy does not correlate directly to the strength of the tested joint. We know some of the factors that influence this process. For example, if the alloy is overheated, the lower melting elements are burned off to a higher degree. This effectively changes the composition of the deposited metal. Thus our advice is to encourage customers to do their own testing of the brazed joint.

But there are some rules of thumb. If customers insist on a certain PSI number, we suggest a number ranging from 60,000-70,000 PSI when tested in the wrought state. Another guideline is that joints properly brazed with Aufhauser Silver Alloys have a shear strength that exceeds three times the shear strength of the thinner, joined metal.



Q: How to join aluminum to copper?

A: It is difficult to braze or weld aluminum to copper, because of the low melting temperature (1018°F) of the aluminum-copper eutectic and its extreme brittleness. By heating and cooling rapidly, however, reasonably ductile joints are made for applications such as copper inserts in aluminum castings. The usual filler metals and fluxes for brazing aluminum to aluminum can be used, or the Silver Alloy filler metals BAg-1 and BAg-1a can be used if heating and cooling are rapid (to minimize diffusion). Pre-tinning the copper surfaces with solder or silver alloy filler metal improves wetting and permits shorter time at brazing temperature. A more practical way to braze aluminum to copper is to braze one end of a short length of aluminum-coated steel tube to the aluminum, and then silver braze the other.



Q: What are differences between brass and bronze?

A: The differences between these two copper-based alloys are summarized in the table below:

  Brass Bronze
Composition Copper and Zinc alloy Copper and Tin alloy, sometimes with Phosphorus, Manganese, Aluminum, or Silicon
Properties Higher Malleability than Zinc or Copper Hard and brittle
Melt Point Lower (~900°C); flows when melted Higher (~950°C) depending on Tin quantity
Corrosion Corrosion resistant (in combination with Aluminum, Silicon, Manganese) Corrosion resistant (especially against seawater)
Fatigue Susceptible to stress cracking when exposed to ammonia. Not as hard as steel. Resists metal fatigue more than steel. Better heat and electrical conductor than most steel.
Color Red to dull yellow, resemblance to gold Reddish brown to dirty yellow
Applications Decorative fixtures
Locks, gears, doorknobs, ammunition
Plumbing valves
Musical instruments
Zippers and fasteners
Spark-resistant fittings and tools
Marine fittings, propellers, submerged bearings
Salt-water corrosion resistant applications
Plumbing fittings
Cast bronze sculpture
Electrical connectors and springs
Bells and cymbals



Q: How to make repairs to cracked steel drum and to prevent re-crack over time due to vibrations from tuning and playing the instrument?

A: Brazing repairs may be made to a crack that is several inches in length, a few tenths of a millimeter in separation. The key point to the repair is to heat the crack as quickly as possible, and to work within the limited time when flux is heated to its ideal working temperature. First preheat the area surrounding the crack to relax and to remove thermal stresses. Clean the affected surface joining area. Braze the crack as quickly as possible: apply flux, heat and braze the filler alloy before the flux stops working (usually within 2 minutes). Choose a low-melting alloy such as BAg-1. Clean the joint making sure to remove any flux residue.



Contact Aufhauser with any other questions