Hi all,

Right to the point: We have a supplier that stamps parts out of T Zero for us then he ships them to a heat treat to bring it up to T6. We call out a spec. of 60 +/- 10 RB. We do not deal with the the heat treater.

We received some parts in that are reading 46/47 RB, the heat treater is claiming that he cannot guaratee a 50 minimum? Can someone clear this up for me?

Why couldn't a 50 minumum be attainable? :confused:

Thanks!

Cordon,

I checked our Aerospace specs, and they show 47/72 RB as acceptable for 6061 T6.

Cordon,

I checked our Aerospace specs, and they show 47/72 RB as acceptable for 6061 T6.

The only thing I could find on it was MIL-H-6088G and it calls out a typical minumum of R/B 42. Back in "2001" I was quoted that 47/80 R/B was the industry standard.

I still can't understand "Why couldn't a 50 minumum be attainable"?

The only thing I could find on it was MIL-H-6088G and it calls out a typical minumum of R/B 42. Back in "2001" I was quoted that 47/80 R/B was the industry standard.

I still can't understand "Why couldn't a 50 minumum be attainable"?

I'm no metallurgist, but I think the fact that you're "aging" the AL after working it might be the issue. The few sources I've had a chance to look at report T6 nominal hardness at 60-65 RB (although most sources report the hardness using the Brinell scale, and report Rockwell hardness as a conversion from it). Here's an example (http://www.matweb.com/SpecificMaterial.asp?bassnum=MA6016&group=General). Note that no range is specified.

The only thing I could find on it was MIL-H-6088G and it calls out a typical minumum of R/B 42. Back in "2001" I was quoted that 47/80 R/B was the industry standard.

I still can't understand "Why couldn't a 50 minumum be attainable"?

The material can only reach a certain Hardness without changing the composition of the Aluminum.

According to MIL-H-6088, (which is now superseded by SAE-AMS-H-6088) calls for E=84 15T=74 in Rockwell readings. You may have to convert it to Brinell Hardness to determine the hardness range.

You may want to purchase the SAE-AMS-H-6088 specification and review those requirements.

These comments are in my opinion, and I could be misreading or determining the composition incorrectly.

Read the standard. :read: is your best source.

With T0 Aluminum, you first heat treat it to AQ (As Quenched) Condition, which is annealed, If not kept in temp below -10F, it will turn to T4 condition.
Then you heat treat it to T6.

The 47/72 RB is from specs of a prime contractor. Actually two of the big ones have the same requirements.

Speaking as a metallurgist, aluminum hardens differently than most steels (precipitation hardening stainless steels such as 17-4 are hardened in the same manner) - it's heated to place the alloying element(s) in solution and then cooled rapidly. Once cooled, it's reheated and held at temperature to precipitate fine 2nd phase particles that cause the hardening phnomenon to occur. Hardness and other related properties typically follow a parabolic curve increasing slowly as the particles initially precipitate and then grow in size and then decreasing once optimum particle size is exceeded.

Parameters that could affect final properites such as hardness include material chemistry - is the alloy near the bottom of the specification range? Rate of cooling and uniformity/control of temperature during aging both have the potential to affect the final results. Another potential avenue to check would be material thickness versus hardness test - is Rockwell B appropriate, or should the hardness be measured as either a superficial scale or another scale such as Rockwell F and then converted to a "B" reading?

Just some thoughts - good luck with your problem.

I'm no metallurgist, but I think the fact that you're "aging" the AL after working it might be the issue.

Jim, could you expand on this a little for me? :)

Jim, could you expand on this a little for me? :)

Well, I just know that sometimes cold-working of metals can alter their mechanical properties, and I was just speculating that perhaps the after-the-fact aging that you're doing might have some bearing on the issue. It's possible that the heat treater is afraid that the exposure necessary to get to the hardness level you need could somehow mess up the parts. I really don't know that much about it, but it does seem to me that the heat treater should have a metallurgist on staff who could answer the question.

Sorry I couldn't be of more help.:(

Well, I just know that sometimes cold-working of metals can alter their mechanical properties, and I was just speculating that perhaps the after-the-fact aging that you're doing might have some bearing on the issue. It's possible that the heat treater is afraid that the exposure necessary to get to the hardness level you need could somehow mess up the parts. I really don't know that much about it, but it does seem to me that the heat treater should have a metallurgist on staff who could answer the question.

Sorry I couldn't be of more help.:(

Jim,

You are absolutely correct, cold working of steel will have hardening effects on it. In the case of Aluminum, you can only clod work up a certain point, and it gets so hard, that no other work can be done without cracking.

This is why we quench them to AQ condition, hold them in low temp until further cold working done, them harden them to T6 or T62 condition.

Jim,
You are absolutely correct
Further proof that sometimes blind squirrels find nuts. :D

As pointed out elsewhere in this thread the "right" path to T-6 is to solution treat then age harden (or precipitation harden ... same thing) shortly thereafter.

It may be there are a couple of things interacting that could reduce the probability that you will achieve the higher end of the hardness range.

The material may have been "sitting" in the O-temper for an extended period ... if so, it may have started its natural aging process (ie moving to a T-4 condition). If that's happened, then the artificial aging treatment to T-6will be compromised ... this because the resulting precipitates will not be of the necessary form.
Further, the cold work (depending upon how much and its proximity to the hardness measurement location) may alter the response to artificial aging.

You may want to experiment by resolution-treating some parts prior to age hardening and see if the response changes.

That being said, let's remember the above discussion on what the industry generally accepts as hardness for T-6.

We ended up talking with the heat treater about this situation and they said that is all that they could guarantee is a 42 R/B as the material spec. is 42 minimum; anything above is a “bonus” so to say. They are running their process for max hardness but still cannot guarantee a 50 minimum. We use another company to stamp some of the same parts and also for different parts that are similar (same material). The other company is using a different heat treat facility and is constantly in the 58/65 R/B range.

I think my next move will be to get a batch of parts to the other heat treat company and see what they can do with them. I have a gut feeling that it’s a material issue as Kevin alluded to; not heat treat.

Thanks for all the help! :)