Variation in Mechanical Properties

[Lescombes]

Hello everyone,

My company procures 92" lengths of 6061-T6 extruded aluminium. The extrusion is a hollow section with an average wall thickness of about 0.1", give or take. Recently we had cause to perform some mechanical testing on a sample of the part. We took six samples from the hollow section, two at each end and two in the middle. The results we got for ultimate and yield strengths were (in metric units):

Ult Yield Elongation %
285 250 10
320 295 8.75
260 250 8.75
305 275 8.75
270 245 10
270 245 8.75

My understanding is that 6061-T6 is solution heat treated and then artificially aged. The minimum requirements for the aluminium's strengths are 262 MPa ultimate and 241 MPa yield.

Whilst the samples meet the strength requirements, are these variations in tensile strengths and elongations normal?

Thank you,
Greg

 

[EdStainless]

Are you sure that you have very accurate area measurements for each sample and not just using the same value for all of them?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Lescombes]

I've just been reviewing the report from our testing service in light of your question. As each sample was a slightly different shape, it appears that yes, unique cross sectional areas have been calculated.

 

[rconner]

Just curious is the "hollow section" that you are cutting test samples from some sort of round, square or what?

 

[metengr]

Yes. I have seen variability like this with data submittals.

 

[WKTaylor]

Lescombes...

I am a bit concerned that a single extrusion would have such widely/variable/marginal tensile readings with significant discrepancies [many LOW values]

Ult/Yield/Elongation %
MPa >>>>>>| KSI [for US] >>>| Sample Spec values [-T6 min,0.050--0.259 thick]
285/250/10.0 | 41.3/36.3/10.0% | 42.0/35.0/12% WW-T-700/6
320/295/8.75 | 46.4/42.8/8.75% | 38.0/35.0/10% AMS-QQ-A-200/8
260/250/8.75 | 37.7/36.3/8.75% | 42.0/35.0/10% AMS4083
305/275/8.75 | 44.2/39.9/7.75
270/245/10.0 | 39.2/35.5/10.0%
270/245/8.75 | 39.2/35.5/8.75%


Did Your material certifications show similar inconsistent/widely-variable tensile, hardness and conductivity readings [AMS2658, AMS-H-6088, etc] on the extrusions that drew Your deeper attention to mandate additional lab tensile testing?

Were the hollow sections made 'special order' per an aerospace or an industrial specification?

NOTE.
6061 extrusion is an old/reliable alloy/temper/process that should NOT be rocket science for reputable extruders to 'nail' consistently.

Regards, Wil Taylor

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[metengr]

The variability could be related to segregation in the original billet.