aluminum brazing 

Brazing of aluminum alloys

 

Aluminum and aluminum alloys can connect a large variety of soldering processes. share brazing or brazing and soldering or soldering. In English, for these types of solder used a variety of terms - brazing and soldering, respectively.

Solid include solders with melting points liquidus, ie the melting end, higher 450 ° C, and also below the temperature solidus, that is, the onset of melting, base metal. Soldering differs from brazing solder melting point - solders melt below the temperature 450 ° C.

Differences between brazing and welding

  • Hard soldering differs from welding in that, that when there is no significant base metal submelting.
  • Brazing temperature is between welding and soft soldering temperatures.
  • Moreover, brazed aluminum structures typically are between welded and brazed soft solders also strength, and corrosion resistance.

Fluxes, the liquidus temperature and the solidus

Soldering of aluminum alloys with hard solders became possible thanks to the development of:

  • fluxes, which destroy the oxide film, without damaging the underlying metal and
  • soldered, which are also aluminum alloys.

(Cm. also Fluxes for aluminum melting)

Solders based on aluminum, used for brazing aluminum alloys, have liquidus temperatures much closer to the temperature solidus base metal, than when soldering most other metals [1].

  • For this reason, soldering brazing, strict temperature control.
  • soldering temperature should be about 40 ° C below the temperature solidus base metal.
  • In some cases, the precise temperature control and the short brazing cycle, This difference may be even 5 ° C.
  • Most aluminum alloy brazing solder at temperatures from 560 to 615 ° C.

Aluminum alloys for brazing

Thermally hardenable wrought alloys, are soldered best, are:

  • 1xxx and 3xxx series alloys, and
  • low magnesium 5xxx series alloys, alloys with a higher magnesium content are more difficult to solder.

Usually well-soldered heat of hardening alloys 6xxx series, for example, 6063 and 6061. Aluminum alloys 2xxx and 7xxx series have low melting temperature and therefore it is difficult to solder, except such as a relatively low-alloy 7004 and 7005 (tables 1 and 2).

Because casting of aluminum alloys is well soldered alloys 356.0, 357.0, 359.0, 443.0, 710.0, 711.0 and 712.0.

Brazing of aluminum brazing product is typically limited thickness not exceeding 0,4 mm. However, in dip brazing and vacuum brazing without flux, the thickness of the workpiece can be as small as 0,13 mm.

Table 1 – Melting ranges and brazeability of common base metal aluminium alloys [1]

Table 2 – Brazeability of aluminium alloys [2]

Industrial solid solders

Industrial solid solders for soldering aluminum and aluminum alloys contain from 7 to 12 % silicon. Lowering the melting point obtained - at some loss in corrosion resistance - by the addition of copper and zinc. Solid solders are aluminum wrought alloy series 4xxx. The most famous of them are welding alloys 4343, 4047 and 4145.

Selection brazing

When brazing with the use of burner commonly used solder liquidus temperature as low as possible from the base metal solidus temperature. Since in this case the temperature control is difficult, melting the large temperature difference will reduce the likelihood of accidental parent metal submelting.

(Cm. The melting point of aluminum alloys)

When it is desired to obtain a tight brazed seam selected solder short melting interval - the minimum difference in temperature between liquidus and solidus. for instance, alloy 4047 It is the interval between the temperatures of the solid and liquid states of all 5,5 ° C. This solder is almost eutectic and quickly turns from a liquid to a solid and strongly reduces soldering time, it is often very beneficial effect on the quality of the soldered seam. This solder is particularly suitable for thin solder joints.

Source:

  1. Aluminum and Aluminum Alloys, ASM International, 1996
  2. Brazing of Aluminum Alloys / Y. Sugiyama // Encyclopedia of Aluminum and Its Alloys – Eds. G.E. Totten, M. Tiryakioğlu, and O. Kessler – 2019 – 171-182