JGEELS
Mechanical
- Jul 10, 2008
- 1
Since the original (Aluminum) 2025-O vs 2024-T3 thread is 'closed', I just wanted to give some clarification, references, and context in response to what I was able to understand from the thread.
My background is as an engineer working in the aerospace manufacturing industry (primarily), having worked in aerospace over fifteen years, primarily and a mechanical manufacturing/process and tool engineer who's worked closely with customers (Design, Manufacturing, M&P, MRB, Quality) over the years regarding the forming/heat treatment, processing, bonding, and assembly of aerospace details (skins, extrusions, 'hogouts', etc.) and subassemblies for regional/business, commercial, and military aircraft and spacecraft. Currently I am working as a senior mechanical (design) engineer at an (aerospace) engineering/manufacturing company in the Wichita, KS area.
In the referenced thread, Reldys Romero asks about specifying 2024-T3 in lieu of 2024-O (to be solution heat treated to -T42). From the thread location, my assumption is that this is a engineering design question, not a repair or production question, although most of the responses were related to production heat treatment tempers, although I may have missed it, I did not see a consistent answer as to the material forms (extrusion, sheet (0-0.250 in), plate (0.250 in - 4.000 (or 8.000) in), billet, or forging), and the only references I saw were an ALCOA forming book and two obsolete links, one to Kaiser products and another to an FAA AMT handbook.
Regarding tempers, assuming a U.S. engineering design, I'd refer to ANSI H35.1 (American National Standard Alloy and Temper Designation Systems for Aluminum). O, T3, and T42 tempers (and other industry standard tempers) are discussed, although some caution should be used as some temper designations are only applicable to limited material forms. For aluminum alloy specific information refer to the AMS-QQ-A-250 specifications, then AMS-QQ-A-250/4 for (general/bare) 2024 alloy, or AMS-QQ-A-250/5 for alclad/clad 2024 alloy. AMS has started creating alloy and temper-specific 4-digit (44xx) specifications, although these are based on/supersede the AMS-QQ-A-250 specifications.
[ul]
[li]O is an annealed condition, which means that most of the residual stresses of the wrought forming processes (F-temper/condition) have been removed by annealing. O (annealed) temper is a common mill temper (for rolling mill materials (e.g. sheet and plate) and extrusion profiles/shapes).[/li]
[li]T3 temper is a solution heat treated material that is cold-worked (usually a level (straight) stretch (hardened by imparting of residual stresses)) then naturally aged. T3 temper is also a common mill temper, although due to the additional work, the raw material is typically more expensive than O (annealed) material.[/li]
[li]T42 temper is a naturally aged condition after starting with O (annealed) condition material and solution heat treatment (/quench) (ref: AMS 2770, s/s AMS-H-6088 and MIL-H-6088). The crystal structure will stabilize (age or precipitation harden) at room temperature within hours after SHT/quench unless retarded (delayed) by placing in a freezer. T4(2) is not typically a mill temper (which you can buy from a mill), but a production temper; ALCOA (now Arconic) typically supplies 2024-T4 material only as coiled sheet, not flat sheet or plate.[/li]
[/ul]
Overall, purchasing the T42 temper formed parts are more expensive than purchasing the same part in T3 temper formed parts, but despite similar (final) properties, there are differences.
[ul]
[li]T3 material (as previously cited) is more expensive to purchase as (mill temper) raw material than O (annealed) condition; Due to the mill cold-work (residual stresses), T3 material requires more force to form, will typically result in more springback, has limited 'formability' (strain), and due to the hardening, is more prone to cracking (often requiring penetrant inspection); however, due to lack of solution heat treatment/quench processes, the T3 formed parts are less expensive. Customers will often cited T3 raw material as both a final temper or to be artificially aged (precipitation hardened) to T8x condition.[/li]
[li]O material is less expensive to purchase as (mill temper) raw material than cold-worked T3 temper raw material. With O (annealed) condition material, the material may be pre-formed (strain (%)) before solution heat treatment (SHT) / quench to AQ (as quenched) or W (unstable crystal structure) material, then (final) formed (again (additional strain (%)), if pre-formed) as soon as possible after quenching (while the material is softer and has not had the time to fully naturally age/stabilize). If the material is allowed to fully naturally age (T4x), it may be just as susceptible to cracking as T3 temper material. T42 material may be artificially aged (precipitation hardened) to T6x to maximize strength, or overaged (T7x) (past maximum strength) to also improve stress corrosion (cracking) resistance. Although rare, there are a few instances of customers specifying (final) 'temper' parts in O condition, but these are typically for special shims or details for a weldment and subsequently heat treated later, although most O (annealed) material will be SHT/quenched and aged to T4x, T6x, or T7x.[/li]
[/ul]
Due to similar final mechanical properties, often customer's material substitution specification allow -T3 temper material to be substituted for -T42 (final temper) material, although usually -T42 cannot be substituted for -T3 (although this may be due to production costs, and less likely due to the slight shortcoming in UTS and 0.2% offset YS relative to T3 temper).
Additionally, while hot forming/hot joggling (like drop hammer forming) seems to be a lost art, a few aerospace manufacturers still do.
Trust but Verify!
Proverbs 3:13; 4:7
James 1:5
Ad Maiorem Dei Gloriam
My background is as an engineer working in the aerospace manufacturing industry (primarily), having worked in aerospace over fifteen years, primarily and a mechanical manufacturing/process and tool engineer who's worked closely with customers (Design, Manufacturing, M&P, MRB, Quality) over the years regarding the forming/heat treatment, processing, bonding, and assembly of aerospace details (skins, extrusions, 'hogouts', etc.) and subassemblies for regional/business, commercial, and military aircraft and spacecraft. Currently I am working as a senior mechanical (design) engineer at an (aerospace) engineering/manufacturing company in the Wichita, KS area.
In the referenced thread, Reldys Romero asks about specifying 2024-T3 in lieu of 2024-O (to be solution heat treated to -T42). From the thread location, my assumption is that this is a engineering design question, not a repair or production question, although most of the responses were related to production heat treatment tempers, although I may have missed it, I did not see a consistent answer as to the material forms (extrusion, sheet (0-0.250 in), plate (0.250 in - 4.000 (or 8.000) in), billet, or forging), and the only references I saw were an ALCOA forming book and two obsolete links, one to Kaiser products and another to an FAA AMT handbook.
Regarding tempers, assuming a U.S. engineering design, I'd refer to ANSI H35.1 (American National Standard Alloy and Temper Designation Systems for Aluminum). O, T3, and T42 tempers (and other industry standard tempers) are discussed, although some caution should be used as some temper designations are only applicable to limited material forms. For aluminum alloy specific information refer to the AMS-QQ-A-250 specifications, then AMS-QQ-A-250/4 for (general/bare) 2024 alloy, or AMS-QQ-A-250/5 for alclad/clad 2024 alloy. AMS has started creating alloy and temper-specific 4-digit (44xx) specifications, although these are based on/supersede the AMS-QQ-A-250 specifications.
[ul]
[li]O is an annealed condition, which means that most of the residual stresses of the wrought forming processes (F-temper/condition) have been removed by annealing. O (annealed) temper is a common mill temper (for rolling mill materials (e.g. sheet and plate) and extrusion profiles/shapes).[/li]
[li]T3 temper is a solution heat treated material that is cold-worked (usually a level (straight) stretch (hardened by imparting of residual stresses)) then naturally aged. T3 temper is also a common mill temper, although due to the additional work, the raw material is typically more expensive than O (annealed) material.[/li]
[li]T42 temper is a naturally aged condition after starting with O (annealed) condition material and solution heat treatment (/quench) (ref: AMS 2770, s/s AMS-H-6088 and MIL-H-6088). The crystal structure will stabilize (age or precipitation harden) at room temperature within hours after SHT/quench unless retarded (delayed) by placing in a freezer. T4(2) is not typically a mill temper (which you can buy from a mill), but a production temper; ALCOA (now Arconic) typically supplies 2024-T4 material only as coiled sheet, not flat sheet or plate.[/li]
[/ul]
Overall, purchasing the T42 temper formed parts are more expensive than purchasing the same part in T3 temper formed parts, but despite similar (final) properties, there are differences.
[ul]
[li]T3 material (as previously cited) is more expensive to purchase as (mill temper) raw material than O (annealed) condition; Due to the mill cold-work (residual stresses), T3 material requires more force to form, will typically result in more springback, has limited 'formability' (strain), and due to the hardening, is more prone to cracking (often requiring penetrant inspection); however, due to lack of solution heat treatment/quench processes, the T3 formed parts are less expensive. Customers will often cited T3 raw material as both a final temper or to be artificially aged (precipitation hardened) to T8x condition.[/li]
[li]O material is less expensive to purchase as (mill temper) raw material than cold-worked T3 temper raw material. With O (annealed) condition material, the material may be pre-formed (strain (%)) before solution heat treatment (SHT) / quench to AQ (as quenched) or W (unstable crystal structure) material, then (final) formed (again (additional strain (%)), if pre-formed) as soon as possible after quenching (while the material is softer and has not had the time to fully naturally age/stabilize). If the material is allowed to fully naturally age (T4x), it may be just as susceptible to cracking as T3 temper material. T42 material may be artificially aged (precipitation hardened) to T6x to maximize strength, or overaged (T7x) (past maximum strength) to also improve stress corrosion (cracking) resistance. Although rare, there are a few instances of customers specifying (final) 'temper' parts in O condition, but these are typically for special shims or details for a weldment and subsequently heat treated later, although most O (annealed) material will be SHT/quenched and aged to T4x, T6x, or T7x.[/li]
[/ul]
Due to similar final mechanical properties, often customer's material substitution specification allow -T3 temper material to be substituted for -T42 (final temper) material, although usually -T42 cannot be substituted for -T3 (although this may be due to production costs, and less likely due to the slight shortcoming in UTS and 0.2% offset YS relative to T3 temper).
Additionally, while hot forming/hot joggling (like drop hammer forming) seems to be a lost art, a few aerospace manufacturers still do.
Trust but Verify!
Proverbs 3:13; 4:7
James 1:5
Ad Maiorem Dei Gloriam
