when the drawing calls out for a 7075-T73 temper, Can I use 7075-T73511 temper? acceptable? 2

[NMHG]

when the drawing calls out for a 7075-T73 temper, Can I use 7075-T73511 temper? acceptable?

How can I prove to my customer the substitution can be made?

 

[SWComposites]

Ah, you should start by comparing the static and fatigue properties of the two materials.

 

[SwinnyGG]

If I was your customer, no.

 

[NMHG]

Can some one help me to understand H35.1 specification?, please and thank you!

 

[WKTaylor]

Monzon... Aluminum alloy temper designations are not a simple Q/A for many reasons.

Refer to Metallic Materials Properties Development and Standardization (MMPDS)-[latest version]... Or the Aluminum Association Aluminum Standards and Data Book [2013 or later].

With specific reference to alloy 7075...

-T73 temper relates to sheet material [0.0040--0.249 thick] or drawn/extruded shapes or forged parts with SHT/QT/Aging HT... with no controlled post HT strain processing.

Whereas -T73511 is a temper exclusive to strain-straightened stretch-relieved extruded parts.
This temper designation applies specifically to extruded parts stretched/compressed after SHT/quench and before aging.... which improves physical properties, such as SCC and EXCO resistance... and usually reduces warpage during follow-on machining/processing. In this case, mechanical properties are lumped together. but physical properties are improved.

As far as H35.1... It is complex to understand... if You DON'T have a baseline understanding of heat treatable and non-heat treatable aluminum alloys.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[AidanMc]

Beware of fixed and frozen process agreements: in my experience in the aerospace industry, you cannot substitute a material called out for without customer approval, regardless of whether or not it's a 'superior' or 'similar' material.

We use two AMS grades of 4340 material and substituted the 'better' vacuum melted one for the air melted one called out for. Our customer was unhappy when they found out we'd made the change without authorization, despite it being a superior grade of the same material.

Aidan McAllister
Metallurgical Engineer

 

[WKTaylor]

NMHG, AidanMc...

I have seen aerospace materials of all types [aluminum, magnesium, steel, CRES Ti, etc] with multiple specifications imprinted on the surface(s) of the raw stock and listed within the certification paperwork provided with that stock. In this instance the raw material vendor certifies that exact piece of material to be equal-to, or better-than, the requirements in each specification listed, by validation/certification testing. This valid practice by the material manufacturers is usually called cross-qualification. This allows the material to be used whenever one of the specs is called out in authoritative engineering data [drawings, etc].

Od, but reassuring, to see [for instance] aluminum sheet metal with AMS-QQ-A-250/X, and AMSXXXX and ASTM BXXX specifications listed... but this happens... and that sheet can be used in many-more applications.

Also, many organizations have engineering substitution or process documents which allow material variations and substitutability. For instance, when approved by engineering in this document: 7075-T73510 or -T73511 extrusions 'could' always replace -T73 extrusions'... but 'never the other-way-around'. Etc... There is economy and efficiency in this practice... but it has to be 'smart' and precise.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[AidanMc]

Oh absolutely. I fully understand having dual certified materials and would be fine in that case. Similarly, if there is an approved engineering document that allows the use of other material specifications, there's no issue in that either.

I was just trying to add an anecdote that using a 'better' material is not always allowed, in the end it comes down to a decision from the group with design authority and needs to be documented.

Aidan McAllister
Metallurgical Engineer

 

[tbuelna]

Can't provide a correct answer to the OP's question. As noted above, in the aerospace industry every process is tightly controlled and no deviations from the controlled process are allowed without approval.

If you want the freedom to use different forms/tempers of a raw material, simply change your drawing note to explicitly allow it.

 

[WKTaylor]

NMHG... depends on what you mean by 'better'.

BETTER-replacement material implies better-for-that-explicit-application [fabrication, assembly, service, repair, etc]... and must be equal or better for secondary real-world considerations such as durability, corrosion resistance, compatibility with finishes, etc, etc.

BAD examples.

A Company M&P engineer used a cookbook formula for a material alternate that was totally inappropriate for the actual application. They had specified a 'better structural alloy'... that MUST NEVER be welded... for a part welded-onto a fuel system pipe. They simply didn't look at the next higher Assy drawings to understand all-aspects of the part. Duhhhh.

I have also seen a range of alternate materials specified that were perfectly adequate for an application on a case-by-case-basis... but these individual alloy/temper variations were allowed on the production drawing or planning documents, which made for an airworthiness/certification tracking-nightmare. In similar instances, an old generation alloy that would have been an acceptable substitute 30-years-ago [with poor SCC properties]... was inadvertently 'allowed' to remain in the 'mix' with newer generation improved materials [toughness/durability, damage tolerance, corrosion resistance, etc]. Guess which more-available material was chosen by the buyers and caused problems very quickly?

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]