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How to solder aluminium
Aluminium is a trickier metal to solder than say copper or steel, and without the right technique it can become an incredibly frustrating exercise. But, with aluminium soldering fast becoming commonplace in vehicles and electronics manufacturing (not to mention its lower price) now is the time to learn the little nuances associated with bonding this lighter, conductive metal.
Based on our knowledge, along with this article on aluminium soldering techniques we have provided this guide on soldering aluminium to give you some tips to help with your next metalwork project.
What is soldering aluminium?
Soldering is the process whereby a low melting point metal alloy (solder) is melted and applied to the joining metals to bond once the solder solidifies.
Soldering is normally used for joining softer metals (like aluminium) to hold them together. The solder is heated to its melting point, turning the solder into a type of liquid for gluing or bonding the metals together.
Which metals are used for soldering aluminium?
Soldering metals can be classified into three different groups based on their melting points:
Low temperature solders
Tin, lead, zinc and cadmium are low temperature solders that produce joints with the least corrosion resistance. The melting point of these solders range from 149°C to 260°C.
Intermediate temperature solders
These solders melt at temperatures of between 260°C and 371°C. Intermediate temperature solders include tin or cadmium combined with zinc, along with small amounts of aluminium, copper, nickel, silver or lead.
High temperature solders
These are typically zinc-based solders with melting points of between 371°C and 427°C. They contain 3 to 10 percent aluminium combined with small amounts of other metals such as copper, nickel, silver and iron. These high zinc solders have the highest strength and provide the most corrosion resistance.
Tips with the aluminium soldering process
Soldering aluminium is somewhat more difficult than soldering other metals (especially if you’re soldering aluminium-to-aluminium), due to the heat required and the potential problems caused by aluminium oxide.
Moreover, some aluminium series are easier to solder than others, and some are currently not possible to solder altogether.
Read on to learn our top tips to help you with the aluminium soldering process.
Preparatory work – cleaning, flux and pre-tinning
Before any soldering commences, we strongly advise cleaning your aluminium to get rid of any unwanted grease and oil.
As aluminium oxide (which all aluminium is coated in) cannot be soldered, it must be scraped off before soldering. We recommend using the right soldering flux to remove the oxide.
What’s more, large joins or aluminium-to-steel metal soldering will benefit from pre-tinning – covering the material with a molten puddle of solder and then rubbing off the surface with a glass fibre brush or wooden stick.
When soldering your aluminium, you will need a large capacity heat source (like a soldering iron, hot air gun or propane torch) to ensure the joint area is warmed to the correct soldering temperature. This can take up to ten minutes because of the high melting point of the solders that are typically used to join aluminium.
When the aluminium has been thoroughly prepared, use your heat source to warm up the joint area. Warm up the solder, and then use the heat source to apply the solder to the applicable areas for bonding.
You should be aware that soldering must be done very quickly before additional aluminium oxide forms as a result of the heat. If the metals do not bond, it’s likely that aluminium oxide has reformed. You will then need to brush and clean the aluminium before trying again.
Summary – general guidelines for soldering aluminium
If you are planning on a project which involves soldering aluminium, then we recommend you follow these guidelines:
- Firstly, all metals should be cleaned to get rid of any grease and oil
- You should then use an appropriate soldering flux to remove any oxide films that forms on the surface of the metals. Pre-tinning is also advised
- Your proposed joint fit should be snug with a gap big enough for the solder
- To achieve the best result when soldering, keep all metal stationary
- Make sure you know the right amount of heat to apply – check the manufacturer’s instructions or check online
Clickmetal is specialist aluminium suppliers
Clickmetal is a leading UK supplier of aluminium and other nonferrous metals. We cut down all metal to size and supply nationwide to both the trade and to domestic customers.