Aluminum 1275: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 1275 is classified within the 1xxx series of aluminum alloys, indicating it is a commercially high-purity wrought aluminium family with minimal intentional alloying additions. The designation implies aluminum as the principal constituent (balance) with controlled trace levels of silicon, iron, copper, manganese, magnesium, zinc and other residuals that influence properties without compromising electrical or thermal performance.

1275 is strengthened primarily by solid-solution effects at trace impurity levels and by strain hardening (work-hardening) rather than by precipitation heat treatment. Its key traits are high electrical and thermal conductivity, excellent corrosion resistance in many atmospheric environments, excellent formability in soft tempers and good weldability; peak mechanical strengths are modest compared with heat-treatable alloys.

Typical industries that use 1xxx-series high-purity aluminum alloys include electrical conductors and bus bars, heat exchangers and heat sinks, chemical process equipment, architectural cladding and decorative components, and some light-gauge automotive and marine parts. Engineers choose 1275 when priority is placed on conductivity, surface finish and corrosion resistance while accepting lower achievable strength than heat-treatable alloys.

1275 is often chosen over lower-cost or higher-strength alloys when the application demands a combination of high thermal/electrical conductivity and excellent malleability for forming complex geometries, or where galvanic compatibility and a bright surface finish are important. Its low alloy content simplifies joining and post-processing while providing predictable, stable behavior over long service lives.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (30–50%)	Excellent	Excellent	Fully annealed, maximum ductility and conductivity
H12	Low-Moderate	Moderate (20–35%)	Very Good	Excellent	Light work-hardening; good for moderate forming
H14	Moderate	Moderate-Low (10–20%)	Good	Excellent	Quarter-hard condition; common for sheet applications
H16	Moderate-High	Low (5–12%)	Fair	Excellent	Half-hard; used when additional stiffness required
H18	High (for 1xxx)	Low (<10%)	Limited	Excellent	Full-hard; lowest formability, highest cold-work strength
T5 / T6 / T651	Not Applicable	N/A	N/A	N/A	1xxx-series alloys are not heat-treatable; T tempers not relevant

The temper chosen for 1275 controls the trade-off between mechanical strength and formability: soft O temper maximizes ductility and conductivity, while H‑tempers introduce work-hardening to raise strength at the expense of elongation. Because the 1xxx family is non-heat-treatable, strength tuning is accomplished by cold deformation, and temper transitions are reversible only via annealing or additional cold work.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.25	Impurity; low silicon helps maintain conductivity and formability
Fe	≤ 0.40	Principal impurity that can cause intermetallics and affect ductility
Mn	≤ 0.05	Minor; limited strengthening role at trace levels
Mg	≤ 0.03	Typically very low; avoids formation of Mg-rich phases
Cu	≤ 0.05	Kept minimal to preserve corrosion resistance and conductivity
Zn	≤ 0.05	Kept low to avoid galvanic issues and maintain ductility
Cr	≤ 0.03	Trace control element; limits grain growth during processing
Ti	≤ 0.03	Grain refiner in cast or billet production; minimal in wrought stock
Others	≤ 0.15 total	Includes residuals such as Ni, Pb, Sn; tightly controlled for performance

The chemical makeup is intentionally near-pure aluminium so that electrical and thermal conduction remain high and corrosion resistance is preserved. Trace elements and residuals are controlled to limit intermetallic particle formation and to retain good cold-working and surface finish characteristics; small amounts of elements such as Ti or Cr are useful during casting and rolling to control grain size and texture.

Mechanical Properties

1275 exhibits tensile behavior typical of high-purity aluminium: relatively low yield and ultimate strengths in the annealed condition, with high ductility and a gradual, uniform plastic deformation response. Yield strength is low relative to heat-treatable alloys, so design must account for lower allowable stresses or use thicker sections. Cold work (H tempers) produces a marked increase in yield and tensile strength but reduces elongation and increases springback.

Hardness correlates with temper: annealed material shows low Brinell or Vickers numbers, and hardness rises predictably with increasing cold work. Fatigue strength is modest and largely dictated by surface finish, residual stresses from forming, and temper state; for cyclic applications careful attention to notch sensitivity and surface condition is important. Sheet thickness influences achievable strength after cold work because thin gauges harden more uniformly and can take higher strain before localized thinning occurs.

Property	O/Annealed	Key Temper (H14 typical)	Notes
Tensile Strength	~55–80 MPa	~100–140 MPa	Values are typical ranges for commercially pure 1xxx alloys; dependent on processing and gauge
Yield Strength	~20–40 MPa	~60–110 MPa	Yield increases substantially with cold working; lower bound in thick heavy-gauge products
Elongation	~30–50%	~10–20%	Elongation drops as temper hardens; measured on standard tensile specimens
Hardness	~15–25 HB	~35–55 HB	Brinell approximate ranges; hardness scales with cold work degree

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for aluminum alloys in the 1xxx series
Melting Range	660–660.5 °C	Near-pure aluminum melting point; narrow melting interval
Thermal Conductivity	~220–240 W/m·K	High conductivity makes 1275 attractive for heat sinks and exchangers
Electrical Conductivity	~60–64 % IACS	Excellent conductor relative to most wrought alloys; depends on impurity levels
Specific Heat	~900 J/kg·K (0.90 J/g·K)	Typical for aluminum near room temperature
Thermal Expansion	~23–24 µm/m·K (20–100 °C)	Significant expansion to accommodate in thermal design

High thermal and electrical conductivities are among the defining physical advantages of 1275, supporting its use where heat dissipation and low-resistivity current paths are needed. The low density and high specific heat benefit lightweight thermal systems and transient thermal management. Thermal expansion is moderate and must be considered in assemblies combining dissimilar materials.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.2–6 mm	Soft in O, strengthened in H‑tempers	O, H12, H14, H16	Widely produced for architectural, electrical and heat-exchanger panels
Plate	6–25 mm	Lower cold-workability per unit thickness	O, H12	Used where thickness and conductivity are required; limited heavy forming
Extrusion	Sectional sizes up to large profiles	Strength depends on post-extrusion cold work	O, H12, H14	Good surface finish; used for bus bars and structural profiles
Tube	Diameter and wall per customer	Behavior similar to sheet; depends on wall thickness	O, H12, H14	Common for conduit, heat exchanger coils and fluid lines
Bar/Rod	Diameters 3–80 mm	Cold work increases strength	O, H16, H18	Used for fasteners, rivets and machined components with high conductivity needs

Forms differ primarily in manufacturability: sheet and thin-gauge products offer the best formability and conductivity while thicker plate and extrusions behave differently under cold work and may be limited to simpler forming operations. Extrusions and tubes are popular for electrical and thermal components because they combine complex cross-sections with excellent thermal pathways and predictable mechanical behavior after tempering.

Equivalent Grades

Standard	Grade	Region	Notes
AA	1275	USA	Designation under the Aluminum Association; near-pure aluminium family
EN AW	1050A / 1060	Europe	Closest commonly available European equivalents in the 1xxx series with similar purity and properties
JIS	A1050 / A1070	Japan	Japanese equivalents are typically in the 1050–1070 range for high-purity aluminium
GB/T	1A00 series	China	Chinese 1xxx series (e.g., 1060) are used interchangeably where 1275 is not specifically listed

Regional standards do not always include a numeric 1275 grade; engineers typically select a 1xxx-series equivalent with comparable minimum purity and residual limits. Subtle differences in allowable impurity limits, surface finish classes and mechanical property tables can affect interchangeability, so vendors' certified composition and property sheets should be consulted for critical applications.

Corrosion Resistance

1275 shows excellent general atmospheric corrosion resistance due to formation of a stable, adherent aluminum oxide film that prevents rapid further attack. In urban and rural atmospheres and many industrial environments it performs very well, and the oxide surface can be enhanced by anodizing for improved wear and decorative finishes.

In marine environments 1275 resists uniform corrosion reasonably well, but it can be susceptible to localized pitting in chloride-rich conditions if roughness or abrasion compromises the oxide. For long-term immersion or splash-zone service, designers often specify protective coatings, cladding or sacrificial cathodic systems to mitigate localized attack and galvanic coupling.

Stress corrosion cracking is rare in low-strength, high-purity aluminium; however, embrittlement risks increase with certain impurity levels, hydrogen uptake or aggressive environments and under tensile residual stresses. Galvanic interactions must be managed carefully because aluminium is anodic relative to many common metals — insulating layers, compatible fasteners or sacrificial anodes are common mitigation strategies.

Compared with higher-alloyed families such as 2xxx (Al‑Cu) or 7xxx (Al‑Zn‑Mg), 1275 provides superior general corrosion resistance but at a cost of lower peak mechanical strength. Compared with pure aluminum 1100 and near-pure grades, 1275 can be considered comparable in corrosion behavior while offering manufacturer-specific processing advantages.

Fabrication Properties

Weldability

1275 welds readily by standard fusion processes such as TIG (GTAW) and MIG (GMAW) because it contains minimal alloying content that would otherwise cause hot cracking. Typical filler alloys include 1100 or Al‑Si fillers (4043) to accommodate solidification shrinkage and to improve fluidity; selection depends on joint design and service requirements. Heat-affected zone (HAZ) softening is minimal because base strength is low, but weld distortion and oxide control require good cleaning and process control.

Machinability

Machinability for 1275 is rated as fair to poor relative to wrought aluminum alloys that contain lead or bismuth free‑machining additives. The alloy tends to produce long, continuous chips and work-hardens locally, so tooling should be sharp and chip evacuation optimized. Recommended tooling includes carbide inserts with positive geometry, moderate feeds and higher cutting speeds than steels; coolant or mist can improve surface finish and tool life.

Formability

Formability in the annealed O temper is excellent and allows for deep drawing, complex stamping and bending with small radii. Best results are obtained in O and light H tempers; heavy H tempers reduce allowable bend radii and increase risk of cracking at strained features. Springback behavior must be accounted for in tooling design, and pre-straining or partial annealing can be used to manage forming limits.

Heat Treatment Behavior

As a 1xxx-series alloy, 1275 is non-heat-treatable: it does not respond to solution-and-precipitation heat treatments to develop higher strength. Strength adjustments are achieved through work hardening (plastic deformation) or by annealing to relieve strain and restore ductility. Typical annealing temperatures for recovery and recrystallization lie in the 300–415 °C range for aluminum, with practical industrial anneals performed near 350–400 °C for controlled durations followed by slow cooling.

Cold working operations such as rolling, drawing and bending generate dislocation structures that raise yield and tensile strength; the degree of strengthening is proportional to total strain. If a softer condition is required after heavy cold work, a full anneal returns the alloy close to the original O temper properties but will reduce conductivity slightly if heating introduces oxidation or contamination.

High-Temperature Performance

1275 retains dimensional stability and corrosion resistance up to moderately elevated temperatures, but mechanical strength drops significantly as service temperature rises above 100–150 °C. Long-term continuous service above ~150 °C accelerates recovery processes and softening as dislocation structures anneal out, which reduces load-carrying capacity. Oxidation is limited to a thin protective alumina scale in air, so chemical attack at high temperatures is typically not severe unless the environment contains aggressive halogens or sulfur species.

Welded joints at elevated temperature can exhibit reduced creep strength and low-temperature embrittlement is not generally a concern; however, designers should derate allowable stresses and consider thermal cycling effects. For applications requiring sustained mechanical strength at high temperature, consider heat-resistant alloy families rather than 1xxx grades.

Applications

Industry	Example Component	Why 1275 Is Used
Automotive	Interior trim and battery bus bars	High formability and conductivity for electrical paths
Marine	Non-structural panels and heat exchangers	Good corrosion resistance and surface finish
Aerospace	Secondary fittings, ducting	Low density, excellent thermal conductivity
Electronics	Heat sinks and thermal spreaders	High thermal conductivity and good machinability for fine features

1275 is often specified where a combination of excellent thermal/electrical conductivity, good corrosion behavior and high formability are required while peak alloy strength is not the governing parameter. Its stability, surface finish options and ease of joining keep it a practical choice across multiple sectors.

Selection Insights

Use 1275 when conductivity and formability are primary design drivers and when you need a predictable, easily weldable aluminum with excellent surface finish properties. It is a practical choice for heat-sinking, bus bars and formed components where heavy structural loads are not the primary concern.

Compared with commercially pure aluminum such as 1100, 1275 typically offers similar conductivity and formability with manufacturer-specific impurity control that may improve mechanical consistency. Versus work-hardened alloys like 3003 or 5052, 1275 trades some strength for superior conductivity and often better brightness; choose 1275 for electrical or thermal performance and 3xxx/5xxx when higher strength or strain-hardening response is required.

When compared with heat-treatable alloys such as 6061 or 6063, 1275 will have significantly lower peak strength but far better electrical/thermal conductivity and formability; select 1275 when conductivity, corrosion resistance and ease of forming/welding are more important than maximum structural strength.

Closing Summary

Alloy 1275 remains relevant because it combines near-pure aluminum conductivity and corrosion resistance with excellent formability and reliable fabrication characteristics, making it a go-to material for electrical, thermal and forming-intensive applications. For engineers who value surface finish, joinability and predictable long-term performance under benign to moderately aggressive environments, 1275 is a practical and cost-effective choice.