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gioasginc (Aerospace) (OP)
22 Aug 09 22:04
Hi, maybe someone can help me in the  next issue:
I tried to achieved  7075-T6 from 7075-T0 ,it is my first time.
The pieces are 0.071" thick.(about 30).Based on technical data I did the following process with the pieces.
1.- (Solution treatment) with the parts (7075-T0) inside the kiln, at maximum rate took 25 minutes to reach the target temperature of 925F, and then I kept that temperature for 1 hour, then stopped the kiln and cool the parts at room temperature.
2.- (Aging) One  hour later when the pieces still inside the kiln and with less than 160F , I reached the target temperature  250F and left them for 24 hours,then cooling at room temperature.
After finishing the process and verifing the results by measuring the hardness of the parts it was less than HRB=60,  when it should be more than 84 to 99 aprox.
two question:
1.-Is there any wrong in my procedure?
2.-As I need to achieve the 7075-T6, and I have to do the correct process again , do I have to do an extra heat treatment because of the previous failed treatment?
gioasginc (Aerospace) (OP)
23 Aug 09 11:09
Helpful Member!  swall (Materials)
23 Aug 09 14:18
You are supposed to water quench from 925F. That is where you went wrong. Just go ahead and repeat the exercise, like you did, except quench in hot water out of the kiln.
gioasginc (Aerospace) (OP)
27 Aug 09 13:09
HI Swall
I followed your instructions and it worked
thanks for all
gioasginc (Aerospace) (OP)
27 Aug 09 16:34
Hi swall
one last question
quenching in hot water, means to keep a temperature of the water  no more than the room temperature, or there is some value of temperature to keep during quenching?
Thanks
swall (Materials)
27 Aug 09 17:01
With hot water, you will get less distortion due to a more uniform residual stress distribution. For a section size/shape that is prone to warping, you would use boiling water. Keep in mind the limitationjs of the quench tank. If it is not temperature controlled, it will heat up anyway as you quench sucessive pieces.
gioasginc (Aerospace) (OP)
27 Aug 09 23:17
it make sense because the pieces experienced some distortion
thanks again Swall
gioasginc (Aerospace) (OP)
1 Sep 09 22:15
I also need a good hardness tester equipment to read HRB,
I am going to work with sheet metal Aluminum alloys from .030" to .125" thickness (7075T6,2024T3,6061T6)
What is the more accurate hardness meter ?  
a portable one or a big one traditional
what brand in recomemdable?
gariartola (Industrial)
2 Sep 09 2:35
One note on distortion during quenching: you can also use up to 34% glicol (Ucon A quenchant, Jo-Quench P-52, Aquatensid BW/RB or similar) in water and have the quenchant media at room temperature. This reduces the cooling speed and as consequently reduces distortion and cracking of the parts due to thermal contractions. It is not as clean as using boiling water but helps in case you can not heat the quench bath.
CoryPad (Materials)
2 Sep 09 8:17
gioasginc,

HRB is an abbreviation for Rockwell B hardness.  This test is unsuitable for testing aluminium alloy sheet.

Regarding testers, don't use portable ones exclusively.  You need to develop a correlation between them and a standard unit.  I recommend Wilson hardness testers:

http://www.wilsoninstruments.com/

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