Aluminum 1N99: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

1N99 is a high-purity wrought aluminum alloy that falls within the 1xxx series of aluminum grades, representing alloys with very high aluminum content and only minor controlled additions. Its composition is designed around a minimum aluminum content near 99 wt% with trace alloying to control grain structure and draw performance. The alloy is predominantly strengthened by strain hardening (work-hardening) rather than by precipitation heat treatment, and it is not a typical candidate for T6-style age hardening.

Key traits of 1N99 include excellent electrical and thermal conductivity relative to more heavily alloyed grades, superior formability in annealed conditions, and very good atmospheric corrosion resistance due to the high aluminum fraction. Weldability is excellent for common fusion processes with minimal hot-cracking tendency, while achievable strength is modest compared with heat-treatable alloys. Typical industries using 1N99 are electrical transmission and buswork, chemical processing, architecture/curtain wall components, and lightweight general-purpose fabrications where high purity and corrosion resistance are prioritized.

Engineers choose 1N99 when the design drivers are conductivity, surface finish, and ductility more than peak strength; the alloy is selected over 1000-series “commercially pure” variants when slightly tighter control of residuals and improved mechanical consistency are required. It is also selected instead of heavily alloyed materials when forming operations are extensive or when post-weld conductivity and corrosion resistance must be preserved.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	Very High	Excellent	Excellent	Fully annealed, maximum ductility and conductivity
H12	Low–Moderate	High	Very Good	Excellent	Light cold work, slight increase in strength
H14	Moderate	Moderate	Good	Excellent	Common commercial cold-work temper for moderate strength
H16	Moderate–High	Moderate	Fair	Excellent	Heavier work-hardening for higher yield
H18	High	Low	Limited	Excellent	Maximum cold work for non-heat-treatable strength
T4	N/A	N/A	N/A	N/A	Not applicable — alloy is not heat-treatable
T6	N/A	N/A	N/A	N/A	Not applicable — alloy does not respond to aging

Temper has a primary influence on 1N99 through the extent of cold work applied after anneal. Annealed (O) material offers the greatest ductility and formability, which suits deep drawing and complex stamping operations, while H‑tempers provide progressively higher yield and tensile strength at the expense of elongation and bendability. Because the alloy is not heat-treatable, tempering is achieved only by mechanical strain; designers must select the minimal cold-work level that meets strength requirements to preserve forming characteristics.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.05	Kept low to preserve conductivity and ductility; high Si reduces formability
Fe	≤ 0.40	Iron is the major impurity; small amounts refine grain but excess reduces ductility
Mn	0.02–0.20	Small Mn can improve strength via dispersoids without appreciable conductivity loss
Mg	≤ 0.10	Limited magnesium to avoid work-hardening acceleration and maintain corrosion resistance
Cu	≤ 0.05	Copper minimized because it reduces corrosion resistance and conductivity
Zn	≤ 0.05	Zinc strictly controlled to avoid embrittlement and SCC susceptibility
Cr	≤ 0.05	Trace chromium can aid grain structure control during processing
Ti	≤ 0.02	Titanium used as grain refiner for extrusion and sheet quality
Others	≤ 0.10	Residuals (each) controlled; total others kept low to maintain high purity

The deliberate control of minor elements in 1N99 balances the need for high electrical and thermal conductivity against the mechanical requirements of forming and service. Iron and silicon are the predominant unavoidable impurities and are tightly limited to preserve ductility and conductivity. Very low additions of manganese and titanium are used selectively to control grain size and to improve mechanical consistency without converting the alloy into a heat-treatable class.

Mechanical Properties

Tensile behavior of 1N99 is characteristic of high-purity aluminum: the annealed condition exhibits low yield and moderate ultimate tensile strength with very high uniform elongation. Cold working will substantially raise yield and tensile strength but at a cost to ductility and toughness; the stress–strain curve becomes progressively more linear and less strain-hardening-capable with increased temper. Hardness correlates with temper and is a convenient in-process indicator of cold-work level.

Fatigue performance in 1N99 is acceptable for non-rotating structural parts but inferior to many alloyed series when subjected to cyclic stresses with high stress concentrations. Thickness effects are notable: thin-gauge sheet will generally achieve higher work-hardening increments during forming operations and may show higher apparent yield than thicker plate at the same temper. Designers should account for reduced fatigue crack growth thresholds relative to harder, alloyed aluminum grades when using 1N99 in dynamic load applications.

Property	O/Annealed	Key Temper (e.g., H14)	Notes
Tensile Strength (UTS)	70–110 MPa	120–170 MPa	Range depends on processing, gauge, test orientation
Yield Strength (0.2% offset)	20–40 MPa	90–140 MPa	Cold work raises yield markedly
Elongation (pct)	30–45%	6–18%	Substantial reduction with increasing temper
Hardness (HB)	15–30 HB	35–70 HB	Hardness correlates with cold-work; anneal is very soft

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for aluminum alloys; enables high specific stiffness/strength
Melting Range	658–660 °C	Narrow melting range for elemental aluminium with minimal alloying
Thermal Conductivity	200–235 W/m·K	Slightly below pure Al depending on impurity level
Electrical Conductivity	60–65 % IACS	High conductivity relative to structural alloys; varies with cold work
Specific Heat	0.90 J/g·K	Near pure aluminum value across typical service range
Thermal Expansion	23 ×10⁻⁶ /K (20–100 °C)	Typical linear thermal expansion for aluminum alloys

Physically, 1N99 behaves like other high-purity aluminums: lightweight, thermally conductive, and with significant heat capacity that is useful in thermal management applications. Conductivity values are sensitive to both chemistry and temper; extensive cold work reduces electrical conductivity due to increased dislocation and impurity scattering. The combination of low density and good thermal/electrical transport makes 1N99 attractive for busbars, heat-spreading panels, and electrical enclosures.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3–6.0 mm	Lower UTS in thin gauges when annealed; work-hardens readily	O, H12, H14	Widely used for cladding, decorative, and conductive applications
Plate	6.0–50 mm	Thick sections show lower work-hardening increments	O, H16, H18	Limited use where heavy section strength is not critical
Extrusion	Wall thickness 1–20 mm	Extrusion seeds a fine grain; as-extruded soft unless cold-worked	O, H12	Common for profiles requiring conductivity and corrosion resistance
Tube	Ø 6–120 mm	Similar to sheet in behavior; cold drawing increases strength	O, H14	Used for conductive tubing and architectural elements
Bar/Rod	Ø 3–50 mm	Solid sections respond to cold drawing and straightening	O, H16	Used for connectors, fasteners where high purity is desired

Forming mode (rolling, extrusion, drawing) and product form determine the microstructure and resultant mechanical behavior of 1N99. Thin-gauge sheet achieves higher effective strength after similar amounts of cold work than thick plate because of strain distribution and process-induced grain orientation. Extrusions and drawn products can benefit from grain-refining titanium additions to provide consistent mechanical properties and improved surface quality.

Equivalent Grades

Standard	Grade	Region	Notes
AA	1N99	USA	Designation used for this high-purity wrought variant
EN AW	1050A (approx.)	Europe	Closest commercial equivalent in the EN system; composition and temper limits may differ
JIS	A1050	Japan	Comparable commercially pure aluminum grade with similar performance envelope
GB/T	1060 (approx.)	China	Local standards with slight compositional and mechanical differences; approximate mapping

Equivalent grades listed are approximate and intended to guide cross-referencing rather than to indicate exact interchangeability. Subtle differences among standards arise from maximum impurity limits, permitted trace elements, and mechanical test methods. When substituting based on equivalence, designers must verify conductivity, impurity content, and temper-specific mechanical data against specification limits to ensure functional interchange.

Corrosion Resistance

1N99 displays excellent general atmospheric corrosion resistance due to the high aluminum content and the alloy's ability to form a stable, adherent oxide film. In rural and industrial atmospheres it performs comparably to other 1xxx-series alloys, with superior resistance to uniform corrosion and good performance in mild urban environments. Pitting in chloride-bearing atmospheres (marine environments) is limited for 1N99, but prolonged immersion or splash zones at high salinities may accelerate localized attack compared with anodized or alloyed 5xxx/6xxx alternatives.

Stress corrosion cracking susceptibility in high-purity aluminum is low compared with 7xxx-series high-strength alloys, because 1N99 lacks the precipitate microstructures that promote SCC initiation and propagation. Galvanic considerations are important: 1N99 is anodic to stainless steels and many copper alloys, and contact with cathodic metals in aggressive electrolytes will accelerate the alloy’s local corrosion. Compared with 5xxx-series (Mg-bearing) alloys, 1N99 trades some mechanical strength for improved overall corrosion stability in mildly acidic or alkaline environments.

Fabrication Properties

Weldability

1N99 is readily welded by TIG, MIG, and resistance methods with minimal hot-cracking provided joint design and fit-up are appropriate. Because of the high purity, weld puddles have good fluidity and the heat-affected zone does not experience significant loss of strength beyond the reducible work-hardening level. Recommended filler wires are high-purity aluminum fillers (e.g., alloy ER1100 or ER1050 family) to preserve conductivity and corrosion resistance, and post-weld anneals are rarely required except where maximum ductility must be restored.

Machinability

As a soft, ductile alloy, 1N99 machines with a moderate machinability index; it is softer than many structural alloys which can lead to built-up-edge and surface finish issues if tooling is not optimized. Carbide tooling with heavy rake angles and reliable chip breakers is recommended, and moderate cutting speeds with higher feeds minimize smearing and promote chip formation. Drilling, threading, and reaming perform well but operators must avoid chatter because the low modulus and ductility can deflect thin sections.

Formability

Formability of 1N99 in O condition is excellent and comparable to the best draw-grade aluminums; the alloy supports deep drawing, roll forming, and complex stamping with low springback. Minimum bend radii are typically low — 1–2× material thickness for mild bends in annealed sheet — while H-tempers require larger radii and may necessitate intermediate anneals. Incremental cold working provides predictable increases in yield, allowing designs to tune strength by controlled forming rather than by alloy substitution.

Heat Treatment Behavior

1N99 is not responsive to metallurgical precipitation heat treatment and is classed as non-heat-treatable. Strength adjustments are achieved via mechanical cold work; to soften the material, full annealing is performed typically at 350–415 °C for times dependent on section thickness followed by slow cooling to avoid warping. No reliable T6 or artificial-aging path exists for this alloy because there are insufficient solute elements to form strengthening precipitates.

Work-hardening is the standard means of strengthening: tensile and yield values increase with the percentage of cold deformation while ductility and fatigue crack-initiation resistance decrease. For production routes requiring a balance, manufacturers employ sequence anneal and controlled cold work passes to reach target mechanical properties and to control residual stresses.

High-Temperature Performance

At elevated temperatures, 1N99 loses strength rapidly; significant reductions in yield and ultimate strength occur above ~150 °C, and usable structural capability is limited beyond 200–250 °C. Oxidation in air is limited to the normal formation of Al2O3, which provides a protective scale but does not prevent loss of mechanical performance. In welded or heat-affected regions, prolonged exposure to elevated temperatures can lead to grain growth and softening; designers should avoid sustained thermal environments when structural stiffness is critical.

Creep resistance of 1N99 is poor relative to hardened or alloyed aluminums, and it is not recommended for sustained-load applications at elevated temperatures. For thermal cycling applications, the high thermal expansion requires careful joint design to mitigate fatigue from mismatch with other materials.

Applications

Industry	Example Component	Why 1N99 Is Used
Electrical	Busbars and conductors	High electrical conductivity and ease of welding
Marine	Exterior cladding and architectural trim	Corrosion resistance and surface finish in non-structural parts
Architecture	Curtain wall panels and louvers	Formability, anodizing compatibility, and visual quality
Chemical Processing	Lightweight tanks and fittings	Purity and corrosion resistance to many chemicals
Consumer Electronics	Heat spreaders / EMI shields	Good thermal conductivity and low density

1N99 is typically specified where high purity, conductivity, and excellent formability are required more than peak structural strength. Its combination of easy weldability and good surface quality makes it a preferred choice for conductive buswork, architectural components, and chemically compatible housings. Manufacturers benefit from predictable cold-work strengthening strategies to tune part behavior without altering base chemistry.

Selection Insights

Choose 1N99 when conductivity, surface finish, and forming capability are primary drivers and when moderate strength obtained via cold work is sufficient. It is especially appropriate for conductive hardware, decorative architectural elements, and chemical-contact parts where corrosion resistance and purity are more important than heat-treatable peak strength.

Compared with commercially pure aluminum (for example 1100), 1N99 offers similar or slightly tighter impurity control with comparable conductivity and formability but may provide marginally better consistency and controlled grain structure. Compared with work-hardened alloys such as 3003 or 5052, 1N99 trades some obtainable strength for superior electrical conductivity and, in many cases, improved surface appearance and anodizing response. Compared with common heat-treatable alloys like 6061 or 6063, 1N99 is preferred when conductivity and corrosion resistance trump the higher peak strength of heat-treated alloys, or when extensive forming precludes post-forming solution/aging cycles.

Closing Summary

1N99 remains a relevant engineering alloy where the balance of high aluminum purity, excellent conductivity, superior formability, and good atmospheric corrosion resistance are required. Its non-heat-treatable, work-hardenable character allows designers to tailor strength through processing without compromising electrical or surface-performance objectives. For applications that prioritize electrical/thermal performance and manufacturability over maximum strength, 1N99 is an efficient, well-understood choice.