Pure aluminium is a relatively soft metal. But when combined with alloying elements it can produce a wide range of mechanical properties. These alloys are categorized into families according to the principal alloying elements with a four-digit identification system. Here is an overview of the of common families of aluminum alloys and their weldability characteristics along with common filler metals:
Almost pure aluminum, at 99% with trace elements making up the rest. This family is used to carry electrical current or for corrosion resistance in particular environments. 1000 series Aluminum alloys are readily weldable with 1100 filler metal.
This is a family of high-strength aerospace alloys. They are extremely sensitive to hot cracking and are the least weldable aluminum alloys. Specifically, 2024 is the least weldable. But there are a couple exceptions, 2219 and 2519, which can be readily welded with 2319 or 4043 filler metal.
A collection of medium-strength aluminum alloys. They are very formable and are often are used for heat exchangers and air conditioners. 3000 series aluminum alloys are readily weldable with either 4043 or 5356 filler metal.
These are typically used as welding or brazing filler alloys rather than base materials. However, when they are used as base materials, 4000 series aluminum alloys are readily welded with 4043 filler metal.
A family of high-strength sheet and plate alloys. 5000 series aluminum alloys are readily welded with 5356 filler metal. However, with stronger alloys such as 5083, 5183, or 5556, filler metals should be used.
6000 series aluminum alloys are tricky to weld because they are prone to cracking. However, with the proper techniques, they can be readily welded using 4043 or 5356 filler metals.
Another group of high-strength aerospace alloys. These alloys are mostly unweldable due to their susceptibility to hot-cracking and stress-corrosion. 7075 is particularly vulnerable. The exceptions are 7003, 7005, and 7039, which are readily weldable with 5356 filler. The alloys can be further classified according to being non-heat-treatable or heat-treatable alloys.