T6 heat treatment, penetration depth?

T6 heat treatment, penetration depth?
I have a centrifugal fan. The blades on the fan are made of 6061 aluminum. The aluminum blades were heat treated to be 6061-T6 Al.
How do I determine the penetration depth of the T6 layer? If the thickness of the blades is too great I can imagine the center of the blade would not have T6 properties.
Is this information available in any text or is this a mass / heat transfer problem?
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Self Balancing wrote:

Yes, this information is available in a text. In most any basic text of metallurgy.
Physical Metallurgy Principles 3RD Edition Robert Reed Hill Practical Metallurgy & Materials 5TH Edition John Neely Serveral more you can find at www.amazon.com......
Here is a hint. There pretty much is no "T6 layer" because .... well T6 isn't associated with surface alloying stuff and for the Aluminum metal series, it typically isn't associated with superficial heating.
Typically, T6 is a specification of a heat-treatment that induces tiny precipitates from constituents that were initially in the 6061 or other aluminum alloy the day the substance was ""born" in the aluminum mill.
There is a lot of good informatin on Aluminum and many other things at this wonderful site:
http://octopus.freeyellow.com/metlinks.html
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I would expect that the blades would be in the T 6 condition throughout their cross section, if they have been heat treated correctly. Typically, the fan blades in question, made from 6061 aluminum alloy, would first be solution treated to place in solid solution the "precipitates" ( alloy constituents) noted. This is accomplished by heating the blades to between 960 and 1075 degrees F. The blades are then held at temperature for a prescribed period of time dependent upon their thickness. After soaking at temperature, the blades would typically be water quenched to room temperature. Removing the blades from the furnace and immersing them into the water quench must occur rapidly, in order to insure that the alloying constituents in the aluminum remain in solid solution as the parts are cooled to room temperature. The transfer time required can be determined by the thickness of the blades.
Immediately after quenching, the blades are in a state known as the W condition. This is an unstable condition, in that, even at room temperature, the strengthening constituents alluded to earlier will precipitate out of solid solution. After 96 hours at room temperature, the blades will reach a strength condition known as T 4.
After solution treating and water quenching to room temperature, if the blades are heated to 340 / 360 F and held at temperature for ~ 8 hours, then cooled to room temperature, they will reach the T 6 condition.
Greg

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Cool post, thanks. I think you just about doubled my knowledge of aluminum metallurgy right here. :) -Alvin in AZ

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I think our motto, as newsgroup posters, is " We live to serve" ! :-)

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