It is well known that metastable nanoscale precipitates contribute to strengthening in age-hardenable aluminium alloys. The precipitates are created when alloying elements cluster during thermo-mechanical processing, and the precipitate crystal structures depend on the composition and temperature history. Needle-like β’’ precipitates grow along the <001> directions in Al and give the main strengthening contribution to the 6xxx series. However, by adding Cu and finetuning the Mg:Si ratio, the phases L and Q’ take form too, contributing to strength and resistance against mechanical degradation during thermal exposure. Understanding how these precipitates respond to external factors like heat input and deformation which happen during welding, can give valuable insight concerning material manufacturing and processing.

In this study, the microstructure of a hybrid metal extrusion & bonding (HYB)-welded Al-Mg-Si-Cu alloy has been investigated on a multiscale, utilizing electron backscattered diffraction and transmission electron microscopy with focus on the heat affected zone. HYB is a novel solid-state welding technique, developed to reduce the strength loss in final products by lowering the heat input during welding.  Using an Al 6082 filler wire to join the Al-Mg-Si-Cu alloy in the T6 condition, microstructure dissolution of strengthening precipitates in and near the welding zone (heat affected zone) have been studied in detail. The microstructure results are correlated with measured mechanical properties and compared with the typically used Al 6082 alloy.