Re:
I would have thought sub-T6 temper would need a treatment to get the strength up post weld. 7020-T4 is down about 30% on proof stress and 15% tensile strength compared to 7020 at T6. So the whole frame would be closer matched to the weld material (at T0), but weaker and softer temper than if it was all aged up to T6.
Any pro metallurgists in the house, this is a bit above my pay grade :shock:
The advice seems to vary quite a lot and since 7005 is only widely available as bike tube, I usually go by the tube manufacturers' guidelines.
Columbus say that their tubing is 7005 supplied in T6 condition, but:
"The heat treatment is strictly recommended, (within?) 4/5 days after welding: artificial ageing 6h at 90° C, then 4h at 150° C."
Dedacciai only say 7XXX for their alloy, but you need to use their own supplied filler rod (5183 I think, as there's no green flare like 5356) and:
"Post welding treatment:120 c° +/- 5 c° 12 / 14 hrs"
Their top V-107 tubing is very different (7003-T6) requires some serious handling, with strict weld sequences and a full quench and age:
Guide here.
The story goes that 7005-T6 was adopted by the Taiwanese bike industry as it could naturally age at room temperature during 6 week surface transit time to the US shipping ports. So maybe, if you can wait a few months before using, no heat treatment is OK. I should run some test pieces...
All the best,