Yes, some aluminum alloy extrusions can be challenging to weld. Indeed, the level of welding difficulty varies from one material to the other. High-strength alloys such as 2024 alloy aluminum extrusion welding and 7075 alloy aluminum extrusion welding are good examples. They present welding issues related to solidification cracking and liquation. But some other alloys are simple to weld. Good examples are alloys in the 5xxx series and 6xxx series.