Help Me Choose

Choosing the Right Alloy and Flux

Making informed decisions about the brazing process involves considering material compatibility, colour match, cost, and the unique challenges of different metals. The following guidelines can help you select the most suitable alloy and flux combination for your brazing applications.

Joining Stainless Steel

For a good colour match, use 455 alloy with HT5 flux. To minimise crevice corrosion, choose a silver solder containing nickel (such as 449 alloy) or use stainless steel grades that already include nickel — for example, 300-series steels like 316.

Making Joints in Close Proximity at Different Times

Where multiple joints are made near each other, use the same silver solder with care and control. Alternatively, start with an alloy of lower silver content and a higher melting range (e.g., 438, 424, or 418) to avoid remelting earlier joints.

Choosing a Cheaper Alloy

If cost is a factor, select an alloy with lower silver content — though this will require more heat and possibly more alloy for good penetration. 455 alloy is often a reliable, cost-effective choice when working with small joint gaps.

Achieving a Good Colour Match on Brass

To improve colour match, try reducing the silver content of the alloy (for example, 430 alloy). Design the joint to minimise visible solder by using a ring or slug of solder and applying heat from the outside, which helps conceal joint lines and enhance the finish.

Joining Cast Iron

Before brazing, remove graphite from the surface by heating the cast iron to a red heat (without flux), then brushing it clean with a stiff wire brush. Apply HT5 flux and proceed with normal brazing.

Joining Aluminium Bronze

To increase flux activity and remove aluminium oxide, add 25% by weight of kitchen salt to EF flux. Use 455 alloy for the brazing process.

Joining Aluminium

Aluminium requires special care due to its oxide layer. Use Stay-Clean Aluminium Flux to achieve proper wetting and bonding. Suitable filler materials include 2207, Alusol, Al12Si, or Technoweld, depending on the alloy and joint type.

Joining Brass

For brazing brass, alloys such as 424, 430, or 445 offer effective solutions, depending on colour match requirements. Keep joints compact and feed the alloy internally to reduce visible solder lines and maintain a clean appearance.

Flux-Coated Rods

Flux-coated rods are available in various alloys and diameters (typically 1.5 mm and above) for general maintenance and for applications where using a paste flux isn’t practical. Heat the joint to a dull red before applying the rod, and carefully control metal flow for best results.