I had a very thin [0.020 thick, clad] sheet of 2024-T3 migrate to -T62 by natural aging in a desert environment for ~20 Years. Very annoying but an important 'learning' moment.
Weldable 6xxx series alloys should NOT naturally age at all... since their aging temperatures are way above 300F. On the other-hand 6013 has a uniquely short time to Age HT from -T4 to -T6 [@375F, 4-to-5-hrs, AMS2770].
IF You are sure it it 6013... accomplish Hardness and electrical conductivity per AMS2658. Caution conductivity may vary out-of-range... but is acceptable if hardness and tensile [per MMPDS] are in-range.
Regards, Wil Taylor
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