2024-T3 Spec for Iridite / Alocrom test panels

I have been using 2024-T3 panels for the salt spray testing of chromate conversions in accordance with AMSC5541 for a couple of years. Thus far I have had no problems (with the panels that is, not the coatings). The panels have been certified as 2024-T3 and the panels themselves have been marked as 2024-T3. However the latest batch to arrive are certified as 2024-T3 but marked as L109. I am informed that the L109 is to the BS or DTD spec and is identical to 2024-T3. I have found on doing my own research that the L109 is in fact clad with 1050A. (The supplier confirms this). As such I would assume that it is un acceptable for the salt spray tests! On further discussions suppliers have told me that all 2024-T3 is clad? Yet on looking in to the problem I have found web sites, predominantly American, offering 2024-T3 bare or clad. I have seen documents stating that 2024-T3A is the clad version. Similarly I have seen documentation stating that L109 is the same as 2024-T3 in its bare state and L110 is 2024-T3 clad. Has anyone else had similar problems? Am I correct in assuming that the AMSC5541 spec is calling for 2024-T3 Bare? Is there a genuine problem with the cross referencing of differing aluminium specs or am I being led up the garden path by a supplier who does not wish to replace 100 panels?

Any help would be appreciated. Rich

The spec specifies AMS2024 T-3 aluminum, not alclad or any substitute. If you ordered that, you should get exactly that and not a questionable substitute. However, It is what your customer will accept. If your vendor could not provide it, exactly as ordered, he should have asked before filling the order.

I feel your suppliers are leading you down the garden path as I regularly run salt spray pieces with 2024 T3 .063 Unclad. I run according to MIL-A-8725F. Check a book on types of aluminum or do a search for QQA250/4 or /5.I believe the /4 is unclad.

Mil-C-5541E, (issue E is the latest) is the military spec for chemical conversion coatings on aluminum & aluminum alloys. 2024-T3 alclad sheet is produced to specifications, AMS4041 & AMSQQA250/5, 2024-T3 bare sheet (i.e., not clad) is produced to specifications, AMS4037 & QQ-A-250/4.

MIL-C-5541E, para 4.3.3 option 2 states "The specimen panels shall be 2024-T3 aluminum alloy panels per QQ-A-250/4 for class 1A coatings & 6061-T6 per QQ-A-250/11 for class 3 coatings".

Therefore, you should be using 2024-T3 BARE sheet. When ordering the metal always quote the full specification to the supplier, in this case 2024-T3 Bare sheet to AMS4037 & QQ-A-250/4.