I have Friction stir welded blanks from AA 6061 T6. The blank thicknesses are 0.5, 1 and 1.6 mm. After welding, it has been observed that the joints are very brittle. I want to improve the ductility of the joints by performing Annealing.
Can anyone suggest the heating rate, holding time and cooling rate for AA 6061 T6 for the mentioned thickness?
Is there any thumb rule to decide the heating and cooling rate for annealing?
Kindly guide.
Thank You.
If your goal is to improve the ductility of the alloy, and as the 6xxx series hardness' comes from hardening precipitation, you may lower the artificial ageing time after annealing or switch to a T4. I suggest you to anneal your alloy for about 6h-12h at 530-550°C. Quench in water. After what, in less than 8h after annealing, you could perform an ageing time of about 4h-6h at 175°C. If the ductility is still not sufficient try a T4 with pre-aging : after annealing, perform a short treatment of 30 minutes at 175°C, then let naturally age you material for about a week.
Another solution is to voluntarily age your T6 to perform a T7 : perform a treatment on your existing alloy of about 4h-6h at 175°C.
You may try to work with the material in T4 condition (as soon as possible to prevent natural ageing) and then age at 190-200°C for 1 hr to end up with a T8 instead
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