For my research work , i am subjecting the duralumin alloy aging process. I am finding quite difficulty in getting repeatable results. Despite best effort, hardness or mechanical strength comes out to be inconsistent.
First i am putting refractory/ceramic brick in both furnace and oven. I keep thermocouple(to nullify temperature gradient mistake) on the floor of the refractory brick and check for the time when temperature reaches the temperature at which the sample needs to be aged. After this, we put the sample inside the furnace at the same point, wait till the temperature again stabilizes to solutioning temperature(ST). It roughly takes about 10-15 mins. As soon as , the temperature reaches to ST, the time is counted. Simultaneously, the oven is also heated to aging temperature, similar to furnace a thermocouple(to nullify temperature gradient mistake) is kept on the floor of the ceramic brick. The oven left to stabilize to the aging temperature. Meanwhile, after the solutioning period is over, the sample is water is quenched in water. After this sample is aging put in oven , which is set at aging temperature, put at same point where thermocouple was put. Similar to furnace, we wait till the temperature stabilizes to aging temperature. Time it takes is around 50 mins to 1 hour. After aging temperature is reached in the thermocouple, time is counted. After the aging time is completed, the specimens are removed, for air cooling. Then the sample is polished for metallographic characterization.
The temper results often fluctuations in terms of hardness and strength, at times too frequenctly. It becomes difficult to find repeatable results.
If some has good hands-on aging process , kindly point my mistake.
Dear Prashant Verma
The repeatability issue you looking for can be totally solve up to the laboratory error percent level with the route: Solution treatment at 500°C (sample temperature) for 1h, water quenched and thermally aged at 180°C (sample temperature) for 8h.
Best regards and wish you success...
Mr. Prashant,
pl check 1. How much time is lost between the time of complete solutionizing and immediate quenching in water. The time gap should not be more than 10 secs.
2. Also ensure that the water is getting agitated during quenching in order to ensure that the heat transfer to water from the specimen is uniform.
3. Check the rise in water temperature after quenching.
4. Is there any time delay between quenching and start of ageing? I t should be very very less.
5. Regarding rate of heating, set temperature for solutionizing and ageing cycle follow the set process.
As a foundry consultant, I had also faced the same issue long time back and after following the above steps, we had a repeatability of 99.5% in results.
Pl try this method and give me feedback.
A.V.Sethuraman
Maybe the microstructure and element distribution are not uniform. Homogenization treatment before solution treatment and aging treatment can improve it.
The answer to this is, dont keep ceramic brick as a insulator platform.
1. Switch on the furnace.
2. Wait till the furnace temperature reaches saturation temp and stabilizes , also cross check with thermocouple.
3. Time approx. is 1 hr 30 min.(when temperature at digital reader and thermocouple have same reading or 1or 2 degree difference).
4. Meanwhile polish the samples upto 1000 grit size , since the material is AlClad. Polishing removes the cladding.
5. Put the sample in middle of the furnace , placing it on alumina crucible(kept inside the furnace since the start, which should have thickness as less as possible and small as it suffice the sample ).
6. Wait till the furnace temp stabilizes again.
7. Meanwhile switch on the oven, check if there is some temperature error using taylor oven thermometer (on the alumina crucible since the start).
8. If there is no temperature error at aging temp, take it out.
9. After the sample have been subjected to solutioning state for appropriate time, water quench it.
10. Place the samples now inside the oven, on the alumina crucible(similar to point 5).
11. Wait for the oven to stabilize the temperature.
12. Once the oven stabilizes , count the time.
13. After the suitable time , take the sample outside.
14. Aircool it.
After failing a lot i got this procedure correct. Most problem is created during homogenization part.
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