Controlled-atmosphere (CAB)
The best fit. 4047 contains almost no magnesium, so it works well with non-corrosive potassium fluoroaluminate flux in a nitrogen furnace.
Brazing filler preform
4047 Aluminium Brazing Disc and Preforms
A 4047 brazing disc is a pre-cut piece of aluminium-12 % silicon filler metal that is placed in or beside a joint and melted in the furnace or by torch to braze aluminium parts together. Because 4047 is close to the aluminium-silicon eutectic, it melts over a very narrow range of about 577 – 582 °C and flows freely into tight joints. Metline supplies 4047 discs, washers, rings and shaped preforms, bare or clad, to drawing, worldwide.
- Alloy
- 4047 (Al-12Si)
- Melting range
- ≈ 577 – 582 °C
- Brazing range
- ≈ 582 – 604 °C
- Forms
- Discs, washers, rings, shapes
What is a 4047 brazing disc?
Brazing joins two parts by melting a filler metal whose melting point is below that of the parts. For aluminium, the fillers are aluminium-silicon alloys, and 4047 is the one with the most silicon: 11 – 13 %. At that level the alloy is nearly eutectic, so it changes from solid to liquid almost at a single temperature rather than over a wide mushy range.
That behaviour makes 4047 the most fluid of the common aluminium fillers. It wets well, fills long capillary gaps and forms smooth fillets, and it leaves a useful margin below the solidus of base alloys such as 1100, 3003, 3103, 6063 and 6951. Discs and other preforms put exactly the right amount of filler where it is needed, which gives more consistent joints than hand-fed rod and suits batch furnace and automated brazing.
Typical preform shapes include flat discs for face-to-face joints (for example a fitting brazed to a plate), washers and rings around tube or stud joints, and custom stamped shapes that match a part outline. Discs can be plain 4047 or clad, where a 3003 core carries 4047 on one or both faces.
4047 chemical composition (wt %)
| Element | Minimum | Maximum | Note |
|---|---|---|---|
| Silicon (Si) | 11.0 | 13.0 | Near-eutectic; lowers melting point |
| Iron (Fe) | — | 0.80 | Impurity |
| Copper (Cu) | — | 0.30 | |
| Manganese (Mn) | — | 0.15 | |
| Magnesium (Mg) | — | 0.10 | Kept low for flux brazing |
| Zinc (Zn) | — | 0.20 | |
| Others, each / total | — | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder |
Aluminum Association limits for 4047. The same alloy is classified as BAlSi-4 in AWS A5.8 and Al 112 in ISO 17672.
Melting and brazing data
4047 filler data
- Solidus
- About 577 °C (1070 °F)
- Liquidus
- About 582 °C (1080 °F)
- Brazing temperature range
- About 582 – 604 °C (1080 – 1120 °F)
- Density
- About 2.66 g/cm³
- Typical joint clearance
- About 0.05 – 0.25 mm for capillary joints
Melting values are approximate and vary slightly within the composition range.
| Filler | Si % | Approx. melting range | Approx. brazing range | When to choose |
|---|---|---|---|---|
| 4047 (BAlSi-4) | 11 – 13 | 577 – 582 °C | 582 – 604 °C | Best fluidity; tight gaps; lowest brazing temperature |
| 4045 (BAlSi-5) | 9 – 11 | 577 – 591 °C | 588 – 604 °C | Most common clad layer for CAB brazing sheet |
| 4343 (BAlSi-2) | 6.8 – 8.2 | 577 – 613 °C | 599 – 621 °C | Less erosion of thin cores; wider melting range |
| 4004 / 4104 | 9 – 10.5 + Mg | ≈ 559 – 591 °C | Vacuum brazing | Magnesium-bearing filler for fluxless vacuum brazing |
Which brazing processes suit 4047 discs?
Torch and induction
Used for repair and small batches. Apply flux to the joint, heat the parts evenly and let the disc melt from the heat of the parts, not the flame.
Vacuum brazing
Plain 4047 lacks the magnesium that disrupts the oxide film in vacuum. Use Mg-bearing 4004 / 4104 preforms, or add a magnesium getter, for fluxless vacuum work.
Dip brazing
Possible in molten salt baths, now less common because of flux handling and cleaning.
Good practice for any route: degrease parts, remove heavy oxide, keep clearances even, fixture parts so the disc stays in contact as it melts, and do not overshoot the brazing range, because excess temperature or time causes the filler to erode thin base metal.
Disc and preform sizes
Supply range (to drawing)
- Thickness
- From thin foil (about 0.05 mm) up to a few millimetres, depending on filler volume needed
- Discs
- Diameters to drawing, from small solder-like discs to large face discs
- Washers and rings
- Inner and outer diameter to drawing, matched to tube or stud size
- Custom shapes
- Stamped, laser-cut or wire-formed preforms
- Construction
- Bare 4047, or clad (for example 3003 core with 4047 one or both sides)
- Packing
- Counted or weighed packs, interleaved to prevent damage, in sealed cartons
To size a disc, estimate the joint volume (fillet plus gap) and add 10 – 30 % for flow losses. A 30 mm diameter, 0.2 mm thick 4047 disc contains about 0.14 cm³ of filler, roughly 0.38 g.
Where 4047 discs are used
- Heat exchangers: fittings, bosses and connectors brazed to tanks, plates and headers
- Cold plates and heat sinks: face-to-face brazing of cover plates and fin packs
- Honeycomb and sandwich structures: bonding aluminium face sheets to brazeable cores
- HVAC and refrigeration: brazed aluminium components and repair parts
- Electrical: busbar and terminal joints where a metallic bond is required
Common mistakes when brazing with 4047
- Brazing 6061, 2xxx or 7xxx alloys: their solidus is too close to (or below) the filler melting range, so the base metal melts or loses strength
- Using plain 4047 in a vacuum furnace without a magnesium source, giving poor wetting
- Overheating or long soak times, which let silicon diffuse into thin parts and erode them
- Leaving flux residues from corrosive (chloride) fluxes, which attack the joint later
- Gaps that are too large; 4047 is fluid, but it still needs capillary action
How to order 4047 discs
- SpecifyShape and dimensions (drawing preferred), thickness, bare or clad construction, quantity and brazing process.
- ConfirmWe confirm alloy certification, tolerances, packing count and delivery terms (EXW, FOB, CIF or DAP).
- ProduceDiscs are stamped or cut from certified 4047 strip or clad sheet and deburred.
- DocumentEach lot ships with a certificate of analysis or EN 10204 3.1 certificate.
- ShipPacked in sealed, moisture-protected cartons for sea or air freight.
References and standards
- AWS A5.8/A5.8M – Specification for Filler Metals for Brazing and Braze Welding
- ISO 17672 – Brazing: Filler metals
- AWS C3.7 – Specification for Aluminum Brazing
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
4047 aluminium (aluminum) brazing disc: frequently asked questions
What temperature does a 4047 disc melt at?
About 577 °C solidus and 582 °C liquidus. Brazing is usually done between about 582 and 604 °C.
Which base alloys can be brazed with 4047?
Alloys with a solidus well above 600 °C, such as 1xxx, 3003, 3103, 6063 and 6951. Alloys such as 6061, 2024 and 7075 are not suitable for furnace brazing with Al-Si filler.
Do I need flux with 4047?
Yes for torch, induction and CAB brazing. For vacuum brazing, use a magnesium-bearing filler such as 4004 or 4104 instead.
What is the difference between 4047 and 4045?
4047 has 11 – 13 % silicon and a very narrow melting range; 4045 has 9 – 11 % silicon and a slightly wider range. 4047 is more fluid; 4045 is the usual cladding on CAB brazing sheet.
Can you make custom preform shapes?
Yes. Discs, washers, rings and stamped shapes can be produced to your drawing in bare or clad material.
Do you ship brazing discs worldwide?
Yes. Metline ships 4047 preforms worldwide with certificates and protective packing.
Need 4047 brazing discs?
Send the drawing, quantity and brazing process. We will confirm construction, certification and a delivered price.
