On occasion, many engineers come across unweldable aluminium alloys. While the majority of aluminum base alloys can be successfully arc welded using the correct welding procedures, there are some alloys which are not. These are  referred to as unweldable.

These groups of alloys, are typically  known as being unsuitable for arc welding. For this reason they are joined mechanically by riveting or bolting.

When we use the term unweldable we mean to describe aluminum alloys that can be difficult to arc weld, without encountering problems during and/or after welding. These problems are usually associated with cracking, most often hot cracking, and on occasion, stress corrosion cracking (SCC).

To get around the unweldable nature of these alloys, a number of high-performance, heat treatable aluminum alloys have been developed by combining various alloying elements in order to improve the materials’ mechanical properties. In some cases, the combination of the required alloying elements has produced materials with high hot cracking sensitivity.