Strengthening in the new aluminum alloy AA 6069

AA 6069, a new aluminum alloy, has been developed for application in hot and cold extrusion and forging. The nominal composition is 0.85% Si, 0.25% Fe, 0.70% Cu, 1.35% Mg, 0.20% Cr, and 0.15% V. Average T6 properties of the ingot without hot or cold deformation are 410 MPa ultimate tensile strength, 375 MPa yield strength, and 12% elongation. Average properties after hot and/or cold extrusion in the T6 condition range from 394–476 MPa ultimate tensile strength, 353 to 448 MPa yield strength, and 14–20% elongation. This alloy also has favorable fatigue, corrosion–fatigue, stress–corrosion, and sustained load cracking properties due to a combination of composition, high solidification rate, thermal and mechanical processing, and T6 practice. Careful TEM, SEM, optical metallography, and EDS were used to characterize the precipitation features and the basis for improved mechanical properties over alloys such as 6061-T6.