AA6061 Percipitation Chart: Hardness Over Time

[snowJT]

I'm not sure if Percipitation graph is the correct terminology for this. But I know there are charts which can show a materials hardness after percipitating over time, then once it percipitates longer than a certain amount of time, it will lose its hardness. I'm specifically looking for AA6061...

Thanks. Kevin.

 

[Astronuc]

I think you are referring to an aging diagram, and the softening, which is related to the coarsening of precipitates, is due to 'over-aging'.

These might be of interest -

Impact of pre-aging on the tensile and bending properties of AA 6061

http://doc.tms.org/ezMerchant/prodt...10-3119/$FILE/MMTA-0610-3119F.pdf?OpenElement Check in the University library for METALLURGICAL AND MATERIALS TRANSACTIONS A.

See also - Accelerated Methods for Characterization of Aging Response



http://mme.iitm.ac.in/kpr/h206061.htm

 

[snowJT]

I'm curious how over aging a material though softens it... you would think instead it would just reach its max hardness, and stay at it no matter how long it was aged for...

(you don't need to have all those links to answer this question, I know that takes a lot of time to do)

 

[snowJT]

for example, here is graph of percipiting.. I'm wondering why you lose hardness after the max is reached, and why it doesn't just stay at its peak.

http://www.hmi.de/bereiche/SF/SF3/materials/light_weight_materials/age_hardenable_aluminium_alloys/fig4.jpg

 

[Astronuc]

I'm curious how over aging a material though softens it... you would think instead it would just reach its max hardness, and stay at it no matter how long it was aged for...

See below.

(you don't need to have all those links to answer this question, I know that takes a lot of time to do)

Not a problem. I find it useful for myself to collect relevant links and put them in one place - PF. Besides, I hope PFers find them useful.


refering to the page - http://www.hmi.de/bereiche/SF/SF3/materials/light_weight_materials/age_hardenable_aluminium_alloys/index_en.html

5. Results

the precipitation sequence of Al-Mg-Si alloys (so called 6000 system)

Age-hardening first produces clusters of a few nm size which are an enrichment of the base material with its alloying elements Mg and Si essentially. Controversy about this stage still persists and research is to be done. Furtheron so called Guinier-Preston zones (G. P.) appear. They are longitudinally shaped and a few lattice constants wide. Growing they transform to needles (ß") and rods of up to hundreds nanometers length (ß’). Equilibrium stage at the end of precipitate growth (not always reached) is the platelet shaped Mg₂Si (ß) phase. All over the precipitation sequence the Mg content of the clusters, zones and particles is increasing monotonically. Maximum hardness is reached when the transition from needles to rods happens (ß" -> ß’), afterwards hardness decreases due to over-aging.

It is unfortunate that this paragraph simply ends with such a simple statement "afterwards hardness decreases due to over-aging" without elaborating why that is.

Think about the aging process - "Age-hardening first produces clusters of a few nm size which are an enrichment of the base material with its alloying elements Mg and Si" - in relationship to the composition in (Al-Mg-Si). For maximum and uniform hardness, one would want the Mg-Si clusters (intermetallic compound) small and evenly/uniformly dispersed. As the aging process continues, the clusters can grow - BUT that means that the base material becomes depleted in the Mg and Si, so what is left is an area/volume with more of the softer Al.

 

[snowJT]

I guess you can think of it as being compared to us. We start off young.. we grow... our strength naturally will increase as we get older... once we reach a certain age range, we are at our peaks... then we keep getting older, and we get weaker.. lol

 

[Astronuc]

I guess you can think of it as being compared to us. We start off young.. we grow... our strength naturally will increase as we get older... once we reach a certain age range, we are at our peaks... then we keep getting older, and we get weaker.. lol

Yeah, and I think I've already passed my half-life. Fortunately, it's all down hill from now on.

 

[snowJT]

you just have to find your re crystalization temperature