The difference between 6061 T6511 vs T651 difference is mainly related to product form and the processing used after heat treatment and stress relief. Both designations refer to stress-relieved tempers of 6061 aluminum, but they should not automatically be treated as interchangeable in every application. The T651 temper indicates that the aluminum has been solution heat treated, artif... https://premiumalu.com/the-ultimate-guide-to-6061-t6511-aluminum/