Aluminum 1A70: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

1A70 is a 1xxx-series aluminum alloy in the commercially-pure family, characterized by aluminum contents near or above 99.7%. As a member of the 1xxx group it is defined by minimal purposeful alloying, with trace amounts of Si, Fe and other residuals rather than deliberate strengthening additions.

The alloy’s strengthening mechanism is predominantly work hardening (strain hardening) rather than precipitation hardening; it cannot be significantly strengthened by heat treatment but responds predictably to cold working and annealing cycles. Key traits include very high electrical and thermal conductivity, excellent resistance to atmospheric and many chemical environments, superior formability in soft tempers, and straightforward weldability with limited hot-cracking tendency.

Typical industries for 1A70 include electrical conductor and busbar manufacture, chemical and food-contact equipment, architectural cladding and trim, heat exchangers and radiator fins, and specialty components where high conductivity and formability are primary requirements. Engineers select 1A70 over strengthened alloys when conductivity, ease of forming, and corrosion resistance are more important than maximizing strength-to-weight or achieving high machinability and hardness.

The alloy is chosen where a blend of near-pure aluminum properties is required: for example where maximum conductivity, deep drawability, or low impurity levels for brazing/fusion processes are required. In many fabrication contexts it serves as the compromise between pure aluminum’s workability and the modest mechanical robustness achievable by strain hardening.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	Very High	Excellent	Excellent	Fully annealed, maximum ductility and conductivity
H12	Low–Moderate	Moderate	Very Good	Excellent	Partial strain hardening; retains good formability
H14	Moderate	Moderate	Good	Excellent	Light cold work; common for drawn sections and strips
H16	Moderate–High	Moderate	Fair	Excellent	Higher strain hardening for added strength
H18	High	Lower	Reduced	Excellent	Heavily strain-hardened for higher static strength
H24	Moderate	Moderate	Good	Excellent	Strain-hardened + partial anneal to balance ductility and strength
T5 / T6 / T651	N/A	N/A	N/A	N/A	Not applicable — 1A70 is non-heat-treatable; T tempers not meaningful

Temper has a first-order effect on mechanical properties and formability for 1A70 because all usable strength is introduced by plastic deformation. Annealed or O tempers maximize elongation and forming limits, making them the default for deep drawing and complex fold work. Increasing H-numbers increases yield and tensile strength while progressively reducing elongation and the ability to form tight radii; weldability remains good across tempers but welded joints can show local softening due to loss of strain hardening.

Chemical Composition

Element	% Range	Notes
Al	Balance (~99.7–99.85)	Bulk of composition; defines conductivity and corrosion behavior
Si	≤0.25	Residual from processing; affects fluidity in casting more than wrought
Fe	≤0.40	Common impurity; can form intermetallics that slightly reduce ductility
Mn	≤0.05	Typically trace; negligible strengthening effect
Mg	≤0.03	Low content; not intentionally added for hardening
Cu	≤0.05	Kept minimal to preserve corrosion resistance and conductivity
Zn	≤0.03	Trace levels; limited effect
Cr	≤0.05	Trace control to limit grain growth in some variants
Ti	≤0.03	Typically used as grain refiner in microalloyed melts
Others (each)	≤0.05	Sum of other residuals limited to maintain high purity

The chemistry emphasizes aluminum as the dominant element with tight limits on impurity elements to preserve conductivity, ductility and corrosion resistance. Small amounts of Fe and Si are unavoidable and can produce fine intermetallic particles that slightly reduce formability at very high thicknesses or after heavy working. The virtually absent Mg, Cu and Zn content prevents precipitation hardening and ensures consistent, predictable behavior under welding and chemical exposure.

Mechanical Properties

Tensile behavior for 1A70 is characteristic of high-purity aluminum: low yield and tensile strengths in annealed condition with high elongation and uniform plasticity. Under cold working (H tempers) both yield and tensile strengths increase substantially while elongation and reduction of area decrease; the stress–strain curve remains ductile but the strain-hardening exponent is modest compared with alloyed series. Thickness and processing history strongly influence measured properties; thin gauge, highly cold-worked strip will exhibit higher apparent strength than thick plate in O temper.

Yield strength in O temper is low (single-digit to a few tens of MPa) compared with heat-treatable alloys, while tensile strength typically ranges in the low double-digit to under 100 MPa depending on temper and thickness. Hardness follows the same trend — low in annealed material and increasing with strain hardening; Brinell values typically sit in the teens for O-temper and rise into the 20s–30s HB for H16–H18 tempers. Fatigue endurance is moderate; fatigue life benefits from the alloy’s ductility but can be reduced by surface defects, severe cold working, or contact with dissimilar metals causing galvanic pits.

Property	O/Annealed	Key Temper (e.g., H14/H18)	Notes
Tensile Strength	60–100 MPa	110–160 MPa	Wide range depending on thickness and degree of cold work
Yield Strength	20–40 MPa	80–140 MPa	H-tempers provide most of usable strength via strain hardening
Elongation	25–45%	2–20%	Annealed has high ductility; heavily-hardened tempers low elongation
Hardness	12–22 HB	20–40 HB	Brinell hardness increases with strain hardening

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for aluminum alloys; useful for lightweight design
Melting Range	~660–657 °C	Pure-aluminum melting point ~660.3 °C; narrow range for high-purity alloy
Thermal Conductivity	~230–240 W/m·K (20 °C)	Very high; close to pure Al values and superior to most alloyed grades
Electrical Conductivity	~60–64 % IACS	High electrical conductivity makes 1A70 a choice for conductors and busbars
Specific Heat	~0.90 J/g·K (20 °C)	Typical of aluminum; useful in heat-sink calculations
Thermal Expansion	~23–24 µm/m·K	Similar to other Al alloys; design for thermal cycling required in assemblies

The physical properties underline 1A70’s appropriateness for thermal and electrical applications: thermal conductivity near the high end for wrought aluminum and electrical conductivity that approaches commercially pure aluminum grades. The alloy’s relatively high thermal expansion coefficient requires careful constraints and tolerancing in assemblies subject to thermal cycling. Melting and casting behavior mirror pure aluminum, which simplifies brazing and fusion joining but requires control of oxide formation.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.2–6.0 mm	Strength varies strongly with temper	O, H12, H14	Widely used for cladding, architectural panels and heat sinks
Plate	6–100+ mm	Lower relative strength per thickness due to low alloying	O, H18	Thicker forms may contain more intermetallics from casting/processing
Extrusion	Complex cross-sections up to large profiles	Strength via cold work and design	O, H14, H16	Good surface finish and excellent formability for thin walls
Tube	Thin- to medium-wall	Strength via drawing and cold work	O, H12, H14	Seamless and welded options; used in heat exchangers and condenser tubing
Bar/Rod	Diameters from small to several inches	Cold-drawn for higher strength	O, H18	Used for conductors, connectors, and rivet-type parts

Sheet and thin-gauge forms are the most common commercial product for 1A70 because they exploit the alloy’s excellent formability and conductivity. Extrusions and tubes depend heavily on draw and subsequent cold work to achieve required strength and dimensional control. Plate and heavy sections are less common because the intrinsic strength is low relative to alloyed series, and thick products can exhibit slightly degraded ductility due to impurity particle distribution.

Equivalent Grades

Standard	Grade	Region	Notes
AA	1070	International / USA	Closest wrought commercial-purity equivalent; similar chemistry and properties
EN AW	1070A	Europe	European designation for high-purity wrought aluminum; comparable limits
JIS	A1070	Japan	Japanese designation for pure-aluminum wrought products with similar uses
GB/T	1A70	China	Chinese standard designation; chemical limits and tempers aligned with 1xxx expectations

Equivalent grades across standards are generally interchangeable for most applications but exact impurity limits and permitted trace elements can shift marginally between standards. These subtle differences can matter in high-conductivity electrical applications or where specific impurity tolerances affect brazing or surface finish. Always cross-reference mill certificates and standards when specifying for regulated or high-performance uses.

Corrosion Resistance

1A70 exhibits excellent atmospheric corrosion resistance due to the rapid formation of a stable, adherent aluminum oxide film on exposed surfaces. In rural and urban atmospheric environments it performs similarly to other high-purity 1xxx series alloys and typically outperforms more active alloy series where copper or high magnesium contents promote localized attack.

In marine and chloride-rich environments the alloy resists uniform corrosion well but, like other aluminum grades, is susceptible to pitting in stagnant saltwater and crevice corrosion in confined geometries. Its low copper content reduces susceptibility to generalized galvanic acceleration, but galvanic coupling to nobler metals (e.g., stainless steel) should be assessed; coupling with cathodic materials can accelerate local attack on fastened interfaces.

Stress corrosion cracking susceptibility is low compared with older high-strength aluminum alloys because 1A70’s low strength and absence of Cu or high Mg prevent the high-strength conditions that encourage SCC. However, anodic dissolution and hydrogen embrittlement phenomena remain concerns under extreme electrochemical conditions. Compared with 3xxx and 5xxx series, 1A70 provides comparable or better uniform corrosion resistance but less structural strength, and compared with 6xxx/7xxx it trades strength for superior general corrosion behavior.

Fabrication Properties

Weldability

1A70 is readily welded by standard fusion processes (TIG, MIG, and resistance welding) with minimal hot-cracking risk because of its low alloy content. Welds will locally lose strain hardening in H-tempers and show softened HAZs that approach annealed properties, so joint design should account for local strength changes. Recommended filler metals are low-alloy or pure-aluminum fillers compatible with the base alloy to avoid creating anodic sites; for conductivity-critical applications use high-purity fillers and control oxides and porosity.

Machinability

Machining 1A70 is more challenging than some alloyed grades because its ductility and tendency to smear can produce built-up edge and gummy chips under improper cutting conditions. The machinability index is modest (lower than free-cutting alloys) and benefits from positive rake tooling, sharp carbide inserts, and coolant to evacuate chips and reduce built-up edge. Higher hardness obtained by cold work improves machinability slightly but also shortens tool life; typical practice uses medium feed rates and moderate cutting speeds with adequate chip breakers.

Formability

Formability is excellent in O temper, enabling deep drawing, spinning, and complex stamping with minimal springback. Bend radii can be tight in annealed sheet; minimum inside radii are typically recommended at 1–2× thickness for most presswork in O temper and increase with H-temper. Cold working is the principal path to increase strength and should be used with staged forming sequences and intermediate anneals when very high reductions are required.

Heat Treatment Behavior

1A70 is non-heat-treatable in the metallurgical sense; it does not develop significant precipitation strengthening with solution treatment and aging. Attempts at conventional T6-style treatments do not produce the characteristic strength gains seen in 6xxx or 7xxx families.

Heat treatment options are restricted to annealing (full softening) and thermal stabilization steps to relieve work-induced residual stresses. Annealing (solution anneal equivalent) is performed by heating into the appropriate temperature range for recrystallization, holding long enough for grain growth control, and controlled cooling; the process restores ductility and conductivity but reduces mechanical strength introduced by cold work.

Temper transitions for product tuning are therefore achieved by cycles of strain hardening and annealing rather than by precipitation sequences. Designers should plan forming and joining sequences around these mechanical processing routes rather than relying on thermal strengthening.

High-Temperature Performance

Mechanical strength of 1A70 degrades rapidly with temperature compared with alloyed aluminum grades and most structural aluminum alloys; above ~150–200 °C the effective strength margin is substantially reduced. For prolonged high-temperature service the alloy is not recommended where mechanical loads must be sustained above that temperature range, because creep and softening become significant.

Oxidation resistance is good because the aluminium oxide scale remains protective; however surface scale and changes in conductivity must be considered for thermal-management components exposed to sustained elevated temperatures. In welded assemblies the HAZ softening experienced at high local temperatures can combine with base-material softening to produce weakness at joints, so design should either avoid sustained elevated temperatures or employ mechanical reinforcement.

Applications

Industry	Example Component	Why 1A70 Is Used
Electrical	Busbars, terminal strips	High electrical conductivity and formability for shaped conductors
Marine	Decorative trim, ducting	Corrosion resistance combined with formability and low weight
Aerospace	Non-structural fittings, thermal shrouds	Good conductivity, light weight, and ease of forming
Electronics	Heat sinks, foil for capacitors	High thermal conductivity and purity for thermal management
Architecture	Cladding, fascia, flashing	Aesthetic finishability, corrosion resistance, and deep-draw capability

1A70 is used where high purity and related physical properties (conductivity, thermal transfer, corrosion resistance) are the design drivers rather than maximum structural strength. Its range of product forms allows use across lightweight structural and non-structural parts, particularly where fabrication processes exploit deep drawing, extrusion, or extensive joining. The alloy’s balance of properties makes it a standard option in specification packages that prioritize conductivity and formability.

Selection Insights

Select 1A70 when electrical or thermal conductivity, superior formability, and corrosion resistance are prioritized over peak mechanical strength. Its low alloy content and near-pure chemistry make it ideal for conductors, heat sinks, and deep-drawn components where cold work can tune strength without compromising conductivity.

Compared with commercially pure aluminum such as 1100, 1A70 trades only small differences in conductivity and impurity limits for broadly similar formability but may feature slightly different mill tolerances; both are chosen for conductivity and ductility rather than strength. Against work-hardened alloys like 3003 or 5052, 1A70 provides comparable or better conductivity and similar formability but lower achievable strength; choose 1A70 when corrosion and conductivity, not strength, dominate. Versus heat-treatable alloys such as 6061 or 6063, 1A70 is chosen when maximum conductivity and forming ability are required despite lower peak strength; use 6061 where structural strength and age hardening are essential.

Closing Summary

1A70 remains relevant as a high-purity, highly formable aluminum alloy whose combination of excellent electrical and thermal conductivity, corrosion resistance, and weldability serve numerous industrial niches. For engineers prioritizing conductivity, deep drawing and chemical compatibility over high structural strength, 1A70 is a practical, cost-effective material choice with predictable processing behavior and wide availability in sheets, extrusions and formed products.