Pure aluminum is a relatively soft metal. But when combined with alloying elements, it can produce a wide range of mechanical properties. These alloys are divided into four categories based on the main alloying elements and a four-digit identification system. Here is an overview of the common aluminum alloy series and their weldability characteristics, as well as common filler metals:
1000 alloys:
Almost pure aluminum, 99% with the remainder made up of trace elements. This series is used to transmit electrical current or resist corrosion in specific environments. 1000 series aluminum alloys can be easily welded with 1100 filler metals.
2000 alloys:
This is a group of high-strength aerospace alloys. They are extremely sensitive to hot cracking and are the worst weldable aluminum alloys. Specifically, 2024 is the most difficult to weld. But there are a few exceptions, 2219 and 2519, which can be easily welded with 2319 or 4043 filler metals.
3000 alloys:
A group of medium-strength aluminum alloys. They are very easy to form and are often used in heat exchangers and air conditioners. 3000 series aluminum alloys weld easily with 4043 or 5356 filler metals.
4000 alloys:
These are usually used as welding or brazing filler alloys, rather than as a substrate. However, when used as a substrate, 4000 series aluminum alloys weld easily with 4043 filler metals.
5000 alloys:
A high-strength sheet and plate alloy family. 5000 series aluminum alloys weld easily with 5356 filler metals. However, for higher strength alloys such as 5083, 5183, or 5556, filler metals should be used.
6000 alloys:
6000 series aluminum alloys are trickier to weld because they tend to crack. However, with proper technique, they can be welded easily with 4043 or 5356 filler metals.
7000 alloys:
Another group of high-strength aerospace alloys. Most of these alloys are not weldable because they are susceptible to hot cracking and stress corrosion. 7075 is particularly susceptible to this effect. The exceptions are 7003, 7005, and 7039, which are easily welded with 5356 filler. These alloys can be further classified as non-heat treatable or heat treatable alloys.