validating Al 2024-T351 with hardness testing
validating Al 2024-T351 with hardness testing
(OP)
I have a 2024-T351 machined part that, since it's manufacure, was found to be made with questionable processes (not enough thermocouples in the heat treating process). The part is a prototype and has been tested and I need to know if the testing was valid in light of the discrepant material.
To validate that the part was not stronger than spec I have had it hardness tested with a result of Rockwell B: 71. This is lower than the MatWeb value of 75 so I tested a sample of clean material with a result of 77- which is higher than the MatWeb value.
The assebly process of the prototype part required heating at 350F for 4 hours. When the sample of test material was heated similarly and then re-tested the Rockwell B went to 83.
Now it looks like the sample became (much) harder after heating and the prototype part is still pretty low after heating.
Is corrolating hardness to strenth a valid method of testing this material?
Does heating this material as described anneal, age or over age?
Thank you!
To validate that the part was not stronger than spec I have had it hardness tested with a result of Rockwell B: 71. This is lower than the MatWeb value of 75 so I tested a sample of clean material with a result of 77- which is higher than the MatWeb value.
The assebly process of the prototype part required heating at 350F for 4 hours. When the sample of test material was heated similarly and then re-tested the Rockwell B went to 83.
Now it looks like the sample became (much) harder after heating and the prototype part is still pretty low after heating.
Is corrolating hardness to strenth a valid method of testing this material?
Does heating this material as described anneal, age or over age?
Thank you!





RE: validating Al 2024-T351 with hardness testing
RE: validating Al 2024-T351 with hardness testing
Mil Hanbook 5 has a plot that shows the "effect of exposure at elevated temperatures on the room temperature tensile ultimate strength". The plot shows a reduction in strength for any heating 200-700F for times .5-10,000 hours and then allowed to cool to room temp.
It is my understanding that a reduction in strength corresponds to a reduction in hardness (and an increase in strength corresponds to an increase in hardness).
Is this not the case for 2024-T351 aluminum plate? Is there some reference that show the correlation?
Thanks.
RE: validating Al 2024-T351 with hardness testing
RE: validating Al 2024-T351 with hardness testing
The plate is 4.5".
RE: validating Al 2024-T351 with hardness testing
RE: validating Al 2024-T351 with hardness testing
I have found a reference that has answered my question regarding suitability of hardness testing to determine strenghth of aluminum. FAA AC 43.13-1B, 'Acceptable Methods Techniques, and Practices of Aircraft Inspection and Repair' states that hardness testing is suitable, within limits, the tensile strength of steel. Furthermore, it notes that hardness testing of aluminum should be limited to distinguishing between annealed and heat-treated aluminum of the same alloy.
RE: validating Al 2024-T351 with hardness testing
RE: validating Al 2024-T351 with hardness testing
I agree pretty much with swall's comments. Hardness testing won't tell you much unless starting from the same piece of material and treating differently.
Heating 2024-T351 for 4 hours at 350oF produces about 1/4 of the transformation to T851, cf. 12 hours at 375oF in ASTM B597.
But, your material has some ambiguity in the amounts of both initial aging and artificial aging.
Comparing the MatWeb pages for 2024-T351 and 2024-T851, the biggest property difference seems to be
Elongation at Break: 19% for T351 vs. 5% for T851.
Maybe worth testing, as probably an important property.
RE: validating Al 2024-T351 with hardness testing
In aerospace we use both hardness and conductivity [%IACS] as a nondestructive quanitification of proper heat treatment.
Refer to AMS2658B for required testing processes and values.
Note for purposes of this spec, -T3 = -T351 = T3511 [etc]
I suspect that conductivity readings will be in the ballpark above -T3... up-to as high as the values for -T6. Believe it-or-not, hardness values for these heat-treat states are about the same.
Regards, Wil Taylor
RE: validating Al 2024-T351 with hardness testing
Thanks guys for all of your help!