I'm not sure if precipitates coalesce with aging (like Ostwald ripening?) so can't directly answer your question.
What I do know is that in Al alloys there are several meta-stable precipitate types that can be present. So it's not just a question of precipitate size and spacing.
e.g. with...
going off the main question but I would say precipitation hardening is usually preferred in Al alloys because it leads to much greater hardness than that from dispersion/decoherent hardening.
But yes decoherent particles are also pretty thermodynamically unstable and there is often a room...
Calculations for n look fine.. I'd say the question is the problem ;)
In fact I'm surprised the answers are even close to reasonable, I'd be worried any time you'd have to do a straight line fit between just two points.
Most the time I have to calculate a slope from data I use 3 to 5 points to...