Aluminum Solid Solution Hardening
Increase in aluminum strength through the incorporation of solute atoms into the crystal lattice, where elastic strains impede dislocation glide.
Solid solution strengthening means the alloying elements sit in the aluminum lattice and block dislocations. That gives strength without heat treatment. It's just there once the metal solidifies. In welding, that's the advantage: such alloys lose little in the heat-affected zone. But be careful with cold-worked or age-hardenable material – strength drops near the weld because deformation or precipitates don't survive the welding heat. The weld stays softer than the surrounding sheet. Use the right filler metal, or the weld will crack. Aluminum conducts heat away well, so work quickly and keep the heat low. Remove the oxide layer right before welding with a brush used only for aluminum. If welding age-hardenable material, check beforehand if you can reheat treat it afterwards – if not, the designer must know that the weld is permanently the weak point.