HELP ME CHOOSE
The easiest and most versatile combination is 455 alloy with EF flux.
The decision to deviate from this combination will be based on other considerations, mainly technical, sometimes financial but will certainly not be based on strength. All silver solders used on properly designed fluxed and heated joints will produce joints stronger than the parent materials. Strength is never an issue.
Aluminium is notoriously difficult to join because of its tenacious and very stable surface oxide. Fluxes to remove that oxide are very aggressive and can have a short life. Using the correct flux overcomes the problems allowing the use of most soft solders. Use Stayclean Aluminium Flux.
is a lead free, low melting point soft solder with excellent flow characteristics and when used with Stayclean Aluminium flux will produce strong leak tight joints in a range of aluminium alloys. It also offers the benefit of a reasonable colour match. The combination will also join aluminium alloys to copper, brass, stainless & mild steel.
is a low temperature flux cored, lead bearing soft solder wire. It is available in 1 metre lengths at 0.9 and 1.5mm dia.
It will readily solder commercially pure aluminium and copper aluminium alloys. It is best heated with a soft propane flame.
is a 12% silicon aluminium rod suitable for general purposes. Use the same principles of brazing to get the best from this alloy although better results are often achieved if the joint is slightly "belled". Because its melting temperature (575 - 585 deg C) is close to that of pure aluminium (620 deg C) care should be taken when heating to avoid melting the surface of the aluminium. The use of propane is recommended. Bring the joint to temperature in 2 - 3 stages, allowing a short period of "soak time" to allow the joint to "soak up the heat". This will help to prevent the components collapsing during brazing. Use it with AlSi Flux.
is more akin to a welding rod and tends to produce fillet joints rather than capillary ones. In simple terms, use a wire brush to clean the joint area, warm it with a propane torch to about 350 deg C, melt the alloy onto the surface, abrade the aluminium through molten Technoweld to effect the joint. It can also be used to repair cracks etc on aluminium castings or build up studs. A pack consists of 5 rods 2.5mm dia x 200. Further details of this alloy and a video link to use it can be found on the Technoweld page under 'Other Silver Solders'.
The joining of brass is quite straightforward (use any silver solder/flux combination) - until the question of colour match enters the equation.
Now the situation becomes more complex.
All silver solders are basically brass with silver and/or cadmium added. This addition is made to lower the melting point of the silver solder to enable you to make joints without melting the parent material.
The downside is that both of these metals are white and change the colour of the alloy. They become lighter in colour.
For a better colour match consider an alloy with less white metal eg 424 containing 24% silver. This has a melting range of 740 - 780°C, but which may be too high.
Perhaps consider 430 containing 30% silver - melting range 665 - 755°C
If the brass is to be polished probably the best one to use is 445 containing 45% silver with a melting range 640 - 680°C.
Keep the joints small, feed the alloy internally (say with a ring or simple preform), heat externally and draw the silver solder through. This will produce the smallest fillets. The extra silver content offers greater reflectivity making the joint line less visible.
Flux Coated Rods
All alloys and of a size of 1.5mm dia and above are available as flux coated rods.
These rods are ideal for general maintenance work and for working in areas where water, to make up the conventional flux paste, may not be available.
The coating is flexible but should still be treated with care to prevent it being damaged.
Best results are obtained with the lower melting point alloys. The joint should be heated generally to a dull red heat before moving the torch to heat the joint to where you want the alloy to flow This creates a heat pattern controlling the metal flow. Apply the rod to the joint.
The flux residues can be removed easily with water and a stiff brush or with citric acid.