Precipitation aging

Kaiser's 7075 tube and pipe sheet lists typical yield strength of 503 MPa for T6 and 434 MPa for T73. The 69 MPa difference is 13.7% of the T6 value. Its tensile data use a 0.500-inch-diameter specimen. Use ordered product requirements and service evidence when assessing a temper substitution. Kaiser typical-property table

Specify the alloy, producer, product form, incoming microstructure and required temper. Aging depends on the preceding thermal and manufacturing route.

Aging can increase strength, but maximum strength is not always the desired service condition. Corrosion resistance, toughness, dimensional stability, formability, and elevated-temperature performance can change with the treatment.

Sequence and terminology

ISO 4885:2026, edition 4, July 2026, describes precipitation hardening treatment as a sequence involving solution treatment, rapid cooling to retain a supersaturated solution, and aging to precipitate compounds. Its vocabulary concerns ferrous materials; use it within that scope rather than treating every definition of “aging” as an aluminum temper definition. In particular, its “natural ageing” entry concerns seasoning cast iron, whereas aluminum suppliers use the same words for room-temperature strengthening. ISO 4885:2026 · Official vocabulary, section 3.5

TWI distinguishes solution treatment, which dissolves constituents and retains them through rapid cooling, from subsequent precipitation hardening. Its technical guidance explains that excessive time and/or temperature can coarsen precipitates and reduce strength. This is a mechanism-level explanation, not a qualified cycle for an arbitrary alloy. TWI heat-treatment methods

“Peak” must refer to a stated property and route. A hardness maximum, tensile-strength maximum, and best component performance need not identify the same condition.

Incoming condition and clocks

Aerometals Alliance's aluminum temper guidance, updated 13 November 2018, distinguishes room-temperature natural aging from artificial aging and separates heat-treatable T tempers from strain-hardened H tempers. It also describes partial annealing and stabilization as different operations. Its values are indicative and explicitly do not replace full product specifications. Do not transfer a generic aging range to every aluminum alloy or interpret a temper suffix as a complete shop instruction. Aluminum temper designations

Record at least the end of solution treatment, transfer to the specified cooling operation, cooling history, storage intervals/temperatures, cold work, and artificial-aging start. The permitted delays and storage controls come from the applicable qualified route. A room-temperature wait cannot simply be subtracted from a furnace hold as though the two exposures had equivalent kinetics.

Cold work can also be an intentional part of the strength-producing sequence. Special Metals' alloy 718 bulletin separately presents cold-work-and-age routes and solution-treatment-and-age routes. These starting conditions are not interchangeable. Identify whether the input is already solution treated, cold reduced, stress relieved, welded, or aged before approving a subsequent operation. Special Metals alloy 718, bolting and fabrication sections

Named alloy examples and tradeoffs

Aluminum 7075: strength versus corrosion requirements

Kaiser's 7075 tube and pipe sheet, printed Rev.05/06, compares T6 and T73. It reports different typical strengths and better stress-corrosion ratings for T73 under its stated rating basis. These are product-specific comparisons, not permission to substitute tempers on a drawing. Kaiser 7075 tube and pipe

ATI 17-4: aging from the specified condition

ATI's 17-4 sheet prints Version 1, 18 August 2016, despite “v2” in the URL. It describes a martensitic solution-treated input, Condition A, strengthened by precipitation of a copper-containing phase. Its heat-treatment table gives H900 at 900 °F for 60 minutes, versus H1150 at 1150 °F for four hours; the detailed table supplies tolerances. These are distinct conditions with different properties, not merely alternative ways to reach the same hardness.

The bulletin separates typical room-temperature data from a table summarizing specified AMS 5604 minima. Do not use its typical values as acceptance limits or assume its historical specification summary replaces the edition governing an order. The broader strength/toughness choice must be made for the actual product and application. ATI 17-4, pages 1 and 4–6

Nickel alloy 718: preserve the complete route

Special Metals' INCONEL alloy 718, bulletin SMC-045, September 2007, describes strengthening by gamma-prime/gamma-double-prime precipitation and the need for the appropriate constituents to be in solution. One stated route uses solution annealing at 1700–1850 °F, rapid cooling, aging at 1325 °F for eight hours, furnace cooling to 1150 °F, and holding there until 18 hours total aging time, followed by air cooling. A separate solution/aging route is also provided. Do not combine the solution step from one route with the aging steps of another without qualification. The producer trademark and historical bulletin are identified here; they do not define every generic UNS N07718 product requirement. Special Metals SMC-045, pages 1–3

Original bounded comparison

Kaiser's 7075 tube/pipe table gives typical yield strengths of 503 MPa for T6 and 434 MPa for T73. The difference is 69 MPa, or 13.7% of the T6 value. Its tensile column uses a 0.500-inch-diameter specimen; these are not design allowables. Kaiser typical-property table

For an original hypothetical comparison, a 20 kN axial load over 50 mm² gives nominal stress of 400 MPa. Ratios of the table's typical yields to that stress are 1.26 and 1.09, respectively. These arithmetic ratios are not safety factors. They omit product minima, orientation, temperature, notches, fatigue, corrosion, and design rules. The example shows why changing to a corrosion-oriented condition requires renewed strength assessment rather than assuming that the alloy number preserves performance.

Process controls and acceptance

Specify part-temperature evidence, hold-time basis, loading, temperature uniformity, cooling, and any allowed interruptions. A furnace setpoint does not prove that the slowest-heating part has completed its required exposure. Conversely, extending a hold to compensate for an uncontrolled load is a process change with possible overaging consequences.

Account for dimensional change through the complete route, including solution treatment, cooling, cold work, aging, and subsequent machining. Measure final features at an agreed reference temperature. Check coatings, inserts, weldments, and assembly constraints against every thermal stage; the aging step cannot be considered independently of those materials.

Acceptance should establish the ordered condition using the applicable product/process specification and tests. Depending on purpose, these may include tensile properties, hardness, electrical conductivity for relevant aluminum controls, corrosion-related tests, microstructure, dimensions, and traceable thermal records. One hardness reading does not independently establish the full aging history or every service property.

A useful order contains four groups of information:

1. Material and input state: producer/grade, product form and dimensions, lot, solution treatment, cooling history, cold work, and previous aging.
2. Required output: exact temper/condition, governing document edition, mechanical and environmental requirements, and prohibited substitutions.
3. Qualified sequence: all stages, delays/storage controls, time-temperature tolerances, load evidence, cooling, and finishing sequence.
4. Acceptance and traceability: test methods/locations, sampling, limits, dimensional checks, thermal records, and deviation disposition.

Related reference

Grades, tempers, and conditions