Aluminum 1250: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 1250 is a member of the 1xxx series of aluminum alloys, which are classified as commercially pure aluminum grades with minimum aluminum content typically above 99%. The 1xxx family is characterized by very low alloying additions; 1250 is among the higher-purity designations in that series and is used where high electrical and thermal conductivity and excellent corrosion resistance are required.

The major alloying elements in 1250 are essentially impurities and trace elements such as silicon, iron, copper, manganese, magnesium, zinc, chromium, and titanium at very low levels. Strengthening is achieved almost exclusively through work-hardening (strain hardening) rather than precipitation hardening, so 1250 is non-heat-treatable and relies on controlled cold deformation (H-temper designations) for elevated strength.

Key traits include very high electrical and thermal conductivity, excellent atmospheric and chemical corrosion resistance, superior formability in soft tempers, and outstanding weldability with minimal hot-cracking tendency. Typical industries using 1250 are electrical (busbars, conductors), heat-exchange and thermal management, chemical processing equipment, architecture, and decorative applications where surface quality and corrosion resistance matter.

Engineers choose 1250 over other alloys when maximum conductivity and formability are priorities and when heavier alloying (for higher peak strength) is not acceptable due to conductivity or corrosion trade-offs. The alloy is selected when a balance of low strength but excellent ductility, surface finish, and corrosion performance yields the best lifecycle or processing economics.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, maximum ductility and conductivity
H12	Low-Medium	Medium-High	Very Good	Very Good	Slight work hardening, retain good formability
H14	Medium	Moderate	Good	Very Good	Quarter-hard; common for formed parts with higher yield
H16	Medium-High	Moderate-Low	Fair	Very Good	Half-hard; used when additional stiffness required
H18	High	Low	Fair-Poor	Very Good	Full-hard; used for spring-like applications and where shape stability needed

Tempers greatly influence the balance between strength and ductility for 1250; soft O tempers maximize drawability and conductivity while H tempers impart strength through dislocation density. Engineers select O for deep drawing or electrical applications, and H14–H18 for components requiring dimensional stability or where cold work provides the required mechanical properties.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.25	Typical impurity; affects fluidity in casting but minimal in wrought 1250
Fe	≤ 0.40	Common impurity that can form intermetallics and slightly reduce ductility
Mn	≤ 0.05	Present at trace levels; minimal strengthening effect
Mg	≤ 0.03	Very low; does not enable precipitation hardening in meaningful amounts
Cu	≤ 0.05	Kept low to preserve corrosion resistance and conductivity
Zn	≤ 0.03	Trace only; higher Zn is avoided to limit susceptibility to embrittlement
Cr	≤ 0.03	Trace amounts may refine grain during processing
Ti	≤ 0.03	Often used as a grain refiner in small amounts during casting/extrusion
Others	≤ 0.15 total	Other residuals; sum of unspecified elements kept minimal per specification

The chemical signature of 1250 is dominated by aluminum with only trace alloying additions, so bulk mechanical properties are governed by purity and cold work. Small levels of Fe and Si form microscopic intermetallic particles that influence recrystallization, grain growth and localized strength, but they do not create heat-treatable strengthening phases.

Mechanical Properties

Tensile behavior of 1250 is typical for commercially pure aluminum: low-to-moderate ultimate tensile strength with excellent uniform elongation in annealed condition and progressively reduced ductility with increasing cold work. Yield strengths are low in O condition and increase with H-tempers, but yield-to-tensile ratios remain such that the material yields early compared with higher-alloyed aluminum grades.

Elongation in O tempers will often exceed 20–35% depending on gauge and processing, while H14–H18 tempers reduce elongation into the single digits for the stiffest tempers. Hardness is low in O conditions (soft, easily scratched) and increases with work hardening; typical Brinell hardness values rise from the mid-teens to mid-thirties as temper increases.

Fatigue performance is modest and largely determined by surface finish, residual stresses from forming, and component geometry; cold-working can raise fatigue strength by introducing dislocation structures that resist cyclic initiation. Thickness effects are significant: very thin gauges (foil) often show higher apparent strength because of rolling-induced strain hardening, while thick sections approach bulk annealed properties and can be more forgiving to localized defects.

Property	O/Annealed	Key Temper (H14/H18 example)	Notes
Tensile Strength	~60–110 MPa	~110–180 MPa	Wide range depending on gauge and degree of work hardening
Yield Strength	~10–40 MPa	~70–150 MPa	H-tempers increase yield substantially via strain hardening
Elongation	~20–35%	~3–15%	O has excellent ductility; H18 can be quite brittle in forming terms
Hardness	HB 15–25	HB 25–45	Hardness increases with cold work; values depend on measurement method

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for pure aluminum; used for lightweight design calculations
Melting Range	~660 °C (liquidus)	Pure aluminum melting point; small impurity content has minimal freezing range
Thermal Conductivity	~210–235 W/m·K	Very high among structural metals; excellent for heat sinks and exchangers
Electrical Conductivity	~34–36 MS/m (~60% IACS)	High electrical conductivity relative to alloyed aluminum series
Specific Heat	~900 J/kg·K	Good thermal capacitance for thermal management
Thermal Expansion	~23–24 µm/m·K	Moderately high expansion; important for joint design in assemblies

The physical property profile of 1250 underpins its primary applications: thermal management and electrical conductance where high conductivity and low weight are required. Density and thermal expansion must be managed in multi-material assemblies, and the high thermal conductivity is retained well even after moderate cold work.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.2–6.0 mm	Strength increases with rolling and light work hardening	O, H12, H14	Widely used for cladding, panels, and heat exchangers
Plate	>6.0 mm	Approaches annealed bulk properties unless cold-rolled	O	Less common than sheet for 1250 due to low strength
Extrusion	Profiles lengths up to several meters	Best in O or lightly worked tempers; can be age-sensitized if impurities present	O, H12	Extrusion benefits from good ductility and surface finish
Tube	Thin- to medium-wall	Strength depends on wall forming process; welded or seamless forms	O, H14	Used in heat-exchange and architectural tubing
Bar/Rod	Diameters up to 200 mm	Often supplied annealed or half hard for machining/forming	O, H14	Common for machined components where conductivity matters

Processing differences determine the available tempers and dimensions; sheet rolling imparts preferred grain flow and surface finish whereas extrusion allows complex cross-sections but requires careful control of impurity content. Applications are matched to form: sheet for formed panels and fins, extrusions for structural profiles and busbars, tubes for heat exchange and fluid handling.

Equivalent Grades

Standard	Grade	Region	Notes
AA	1250	USA	Direct designation in some legacy and commercial lists; essentially a high-purity 1xxx series alloy
EN AW	1250A / 1050A comparable	Europe	EN designations for 1xxx series (1050A / 1200 series) overlap in properties; direct 1250 designator used in some supply chains
JIS	A1050 / A1100 comparable	Japan	JIS commonly lists A1050/A1100 as commercially pure grades with similar attributes; 1250 maps functionally to these for many uses
GB/T	1250 or 1050 equivalent	China	Chinese standards include 1xxx series purity classes; local grade numbering can differ but functional equivalence exists

Regional standards and commercial grade names can vary and direct one-to-one equivalence is sometimes approximate; users should verify purity, impurity limits and mechanical property requirements rather than rely solely on a grade number. Surface finish, temper availability, and certified conductivity often drive selection across regions more than the nominal grade label.

Corrosion Resistance

In atmospheric environments 1250 exhibits excellent general corrosion resistance due to the protective aluminum oxide film that forms spontaneously on the surface. The high purity minimizes galvanic heterogeneity and localized cells, so uniform corrosion rates are low in urban and rural atmospheres.

In marine and chloride-bearing environments 1250 performs well for non-structural and mildly stressed components, although pitting resistance is slightly inferior to certain 5xxx and 6xxx alloys when exposed to aggressive seawater under mechanical stress. Stress corrosion cracking is uncommon in commercially pure alloys like 1250; the primary concern in aqueous chloride environments is localized pitting around contaminants or dissimilar-metal contact points.

Galvanic interactions should be considered when 1250 is coupled to more noble metals such as stainless steels or copper; as the less noble partner it will corrode preferentially in the presence of an electrolyte. Compared with higher-alloyed series (2xxx, 7xxx), 1250 offers superior corrosion resistance but at substantially lower mechanical strength, whereas 5xxx alloys (Mg-bearing) provide a compromise between strength and corrosion resistance that can outperform 1250 in some marine structural applications.

Fabrication Properties

Weldability

1250 is highly weldable by common fusion processes (TIG, MIG, resistance welding) because of its low alloy content and excellent ductility. Hot-cracking risk is minimal compared with higher-alloyed aluminum series, and weld HAZ softening is not a critical issue because the alloy is non-heat-treatable; however, filler selection should consider joint conductivity and corrosion compatibility. For electrical or thermally critical welds, use filler alloys with compatible conductivity and mechanical behavior and control heat input to minimize distortion.

Machinability

Commercially pure 1250 has moderate machinability; it tends to be gummy compared with higher-strength alloys, and chips can be long and continuous unless chip-breaker geometries and interrupted cutting are used. Carbide tooling with positive rake and good chip evacuation is advised, and cutting speeds should be optimized to avoid built-up edge and poor surface finish. Because the alloy’s low strength reduces cutting forces, high feed rates are possible, but tool wear can be accentuated by adhesion and rubbing.

Formability

Formability is excellent in O and lightly worked tempers, enabling deep drawing, complex stamping, and extensive bending with small bend radii relative to higher-strength aluminum alloys. Recommended minimum bend radii are small in O condition — often expressed as R/t ≤ 1–2 for simple bends depending on tooling and surface condition — while H14–H18 tempers require larger radii and may necessitate pre-heating or intermediate anneals for severe forming. Cold-working increases strength but reduces stretchability and increases springback, so process planning must balance final temper versus forming sequence.

Heat Treatment Behavior

As a non-heat-treatable alloy, 1250 does not respond to solution treatment and artificial aging to increase strength via precipitate formation; the microstructure lacks sufficient alloying elements to form strengthening phases. Strength modulation is therefore achieved by mechanical deformation levels (H-tempers) and by annealing recrystallization cycles to soften the material when required.

Typical thermal cycles for processing include full anneal at temperatures near 350–400 °C for wrought products to restore ductility, followed by controlled cooling to avoid excessive grain growth. Repeated cycles of cold work and anneal allow manufacturers to tailor strength and ductility for specific forming or service requirements, and grain refinement via small additions of titanium or other refiners during casting or melting may be used to improve mechanical uniformity.

High-Temperature Performance

1250 retains usable mechanical properties at mildly elevated temperatures, but strength degrades steadily with temperature and is not recommended for load-bearing applications above approximately 150–200 °C. Creep resistance is limited because of the low alloy content; long-term exposure to moderate temperatures accelerates recovery and softening, particularly in H-tempers that derive strength from dislocation structures.

Oxidation at elevated temperatures is limited to the formation of alumina, which is protective in many environments, but prolonged high-temperature exposure can cause embrittlement and grain growth that reduce toughness. The heat-affected zone around welds can experience microstructural changes, but because 1250 is non-heat-treatable there is no classic HAZ softening as seen in age-hardenable alloys; nevertheless, thermal cycling can relax stresses and diminish cold-work-strengthened properties.

Applications

Industry	Example Component	Why 1250 Is Used
Electrical	Busbars, conductor strips	High electrical conductivity and good surface finish
Marine	Heat-exchanger fins, cladding	Excellent atmospheric corrosion resistance and formability
Aerospace	Non-structural fittings, shims	High conductivity and low density for thermal and electrical uses
Electronics	Heat sinks, thermal spreaders	Exceptional thermal conductivity and ease of fabrication

1250 is widely used where conductivity and formability trump the need for high structural strength. Its combination of low density, high thermal/electrical conductivity and excellent corrosion resistance make it a durable choice for electrical, thermal-management and architectural components where heavy alloying would be detrimental.

Selection Insights

1250 is a practical choice when maximum electrical or thermal conductivity, excellent formability and corrosion resistance are priorities and when structural strength requirements are modest. Compared with commercially pure aluminum 1100, 1250 typically offers similar conductivity but can differ in impurity limits—select based on certified conductivity, temper availability and supplier control rather than name alone.

Compared with work-hardened alloys such as 3003 or 5052, 1250 trades lower strength for higher conductivity and often better general corrosion resistance; choose 1250 when conductivity or forming is more important than yield strength. Against heat-treatable alloys such as 6061 or 6063, 1250 provides superior conductivity and formability but lower achievable peak strength; it is preferred when conductivity, surface finish, or chemical resistance justify accepting lower mechanical strength.

When selecting 1250, weigh the need for annealed formability and conductivity against availability of tempers and sheet thicknesses, and verify that fatigue, creep or high-temperature requirements are within the alloy’s limited envelope.

Closing Summary

Alloy 1250 remains relevant because it delivers an exceptional combination of high electrical and thermal conductivity, excellent corrosion resistance, and superior formability in a low-density material that is easy to weld and process. For applications where conductivity, surface quality and ductility are the primary design drivers, 1250 provides a cost-effective and reliable engineering solution.