Aluminum 4028: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 4028 is a member of the 4xxx-series aluminum alloys, a family characterized by silicon as the principal alloying addition. It is a silicon-rich, microalloyed grade that also contains controlled amounts of magnesium and transition elements to provide a balance between strength, weldability, and formability.

The alloy achieves strengthening through a combination of controlled solid-solution effects, fine silicon dispersoids and limited precipitation from Mg-Si clusters; in practice it behaves as a semi-heat-treatable alloy with good response to solution treatment and artificial aging, while also responding well to work hardening. Typical traits include moderate to high tensile strength in aged tempers, good corrosion resistance in atmospheric environments, excellent weldability using Al-Si filler alloys, and favorable formability in the annealed condition.

Industries that commonly use 4028 include automotive structural and trim components, marine fittings and housings, consumer appliances, and some aerospace secondary structures where a balance of formability and strength-to-weight is required. The alloy is selected where designers need better strength than commercially pure grades without compromising welding and extrusion performance.

4028 is often chosen over 1000/3000-series alloys when higher strength and dimensional stability are required, and over 6xxx-series alloys when improved weldability and silicon-directed casting/extrusion behavior are prioritized. Its semi-heat-treatable nature makes it attractive where post-fabrication aging is feasible but extreme peak strengths are not essential.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (20–30%)	Excellent	Excellent	Fully annealed, maximum ductility and formability
H14	Medium	Moderate (12–18%)	Good	Excellent	Work-hardened single-step strain hardening for moderate stiffness
H24	Medium-High	Moderate (10–15%)	Fair-Good	Excellent	Strain-hardened and partially stabilized, good springback control
T4	Medium	Moderate (12–18%)	Good	Excellent	Solution heat-treated and naturally aged, balanced properties
T5	Medium-High	Lower (8–14%)	Fair	Very Good	Cooled from elevated temperature and artificially aged, faster production aging
T6 / T651	High	Lower (8–12%)	Fair-Poor	Very Good	Solution treated and artificially aged for peak strength; T651 includes stress relief

Temper directly governs the strength–ductility trade-off for 4028 and controls formability for stamping and deep drawing operations. Annealed O-temper provides maximum elongation and lowest yield, while T6/T651 achieves the highest usable strength at the cost of reduced bendability and increased springback.

Chemical Composition

Element	% Range	Notes
Si	0.9–1.8	Primary alloying element; improves fluidity, reduces melting range, and aids weldability
Fe	0.4–1.0	Impurity that forms intermetallics; controlled to limit loss of ductility
Mn	0.05–0.50	Grain structure modifier and dispersoid former for strength and toughness
Mg	0.15–0.60	Enables limited precipitation strengthening (Mg-Si clusters) and increases strength
Cu	0.02–0.30	Low levels to assist strength but kept limited to maintain corrosion resistance
Zn	0.02–0.25	Minor addition, generally limited to avoid SCC susceptibility
Cr	0.01–0.10	Controls grain structure and reduces recrystallization during processing
Ti	0.02–0.12	Grain refiner used in primary metallurgy for fine microstructure
Others	0.05 max (each) / 0.15 total	Includes trace elements such as Zr, Sr; kept low to avoid deleterious phases

The silicon concentration defines much of 4028’s behavior: it improves castability and weld filler compatibility while reducing solidification range. Magnesium and manganese operate synergistically to enable modest age hardening and refine the as-processed microstructure, while iron and other impurities need tight control to prevent coarse intermetallics that reduce ductility and fatigue life.

Mechanical Properties

In tensile behavior, 4028 shows a marked difference between annealed and aged tempers. Annealed (O) condition yields low tensile and low yield but high elongation, facilitating deep drawing and complex forming; aged tempers (T5/T6) produce a tighter yield–tensile spread and higher ultimate strength suitable for structural components.

Yield strength rises substantially with solution treatment and artificial aging, typically reaching 60–70% of ultimate tensile strength in T6-like conditions. Fatigue performance is influenced by surface condition and cold work; polished and shot-peened parts exhibit improved endurance limits while coarse intermetallics from high Fe can act as crack initiation sites.

Hardness correlates with temper; annealed parts are soft and easily machined, while T6 surfaces reach higher Brinell or Vickers numbers consistent with increased dislocation density and precipitate strengthening. Thickness affects both hardening response and quench rates during solution treatment, so parts above several millimeters require controlled thermal cycles to achieve uniform properties.

Property	O/Annealed	Key Temper (T6/T651)	Notes
Tensile Strength	95–140 MPa	210–270 MPa	T6 values depend on section thickness and aging curve
Yield Strength	35–60 MPa	140–200 MPa	Yield increases strongly with artificial aging
Elongation	20–30%	8–12%	Elongation decreases as strength increases
Hardness (HB)	25–40 HB	60–90 HB	Hardness tracks tensile strength and affects machinability

Physical Properties

Property	Value	Notes
Density	2.70–2.73 g/cm³	Typical for aluminium alloys, good strength-to-weight ratio
Melting Range	~570–640 °C	Alloying depresses and broadens the melting interval versus pure Al
Thermal Conductivity	120–150 W/m·K	Lower than pure Al; silicon and alloying reduce conductivity modestly
Electrical Conductivity	~28–42 % IACS	Depends on temper and alloying; lower than pure or 1xxx-series alloys
Specific Heat	~900 J/kg·K	Typical aluminium specific heat, useful for thermal management
Thermal Expansion	22–24 µm/m·K (20–100 °C)	Comparable to other Al alloys; important for joint design with dissimilar metals

4028’s physical properties make it a favorable choice for components requiring thermal management and lightweight construction. The alloy’s thermal conductivity is sufficient for heat-sink-like applications while its electrical conductivity is reduced relative to pure Al, so it is seldom used where maximum conductivity is required.

Thermal expansion and melting range must be considered in welded assemblies and high-temperature processing. Design allowances for differential expansion and accurate control of heating/cooling rates during heat treatment are necessary to avoid distortion.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.2–6.0 mm	Uniform through rolling; good formability in O/T4	O, H14, T4, T5	Widely used for stamped parts and housings
Plate	6–50 mm	Lower quench efficiency; requires thicker solution treatment cycles	O, T4, T6 (limited)	Heavy sections need special aging to reach target properties
Extrusion	Profiles up to 200 mm	Good strength and dimensional stability after aging	O, T5, T6	Silicon aids extrusion fluidity and surface finish
Tube	0.5–10 mm wall	Similar behavior to sheet; bending and hydroforming in annealed state	O, H24, T6	Common for chassis components and conduit
Bar/Rod	Ø3–100 mm	Good machinability in O; aged bars used for fittings	O, T6	Drawn and straightened for precision parts

Sheets and extrusions benefit from the alloy’s balance of fluidity and strength; thin-gauge parts can be solution treated and rapidly quenched for better aging response. Thick plates require longer solution-treatment cycles and controlled quenching to avoid centerline softness and uneven properties.

Extruded profiles leverage silicon to reduce die wear and improve surface finish, while tubes and bars are frequently supplied in annealed conditions for forming or in aged tempers for mechanical components. Processing route selection affects final microstructure and must align to component geometry and required property set.

Equivalent Grades

Standard	Grade	Region	Notes
AA	4028	USA	Industry designation for wrought 4xxx microalloyed variant
EN AW	AlSi1MgMn	Europe	Approximate equivalent chemical basis; regional temper codes apply
JIS	A4028 (approx)	Japan	Local designations vary; heat treatment cycles tailored regionally
GB/T	4028	China	Often produced with similar chemistries but with local manufacturing tolerances

Regional standards may use different alloy numbering conventions and tolerances, so direct substitution requires verification of exact chemical ranges and mechanical property guarantees. Small differences in impurity limits, grain refinement practice, and permitted trace elements can affect fatigue life and weldability, so engineering cross-reference should include specification sheets and test data.

Corrosion Resistance

In atmospheric environments 4028 exhibits good general corrosion resistance, benefitting from silicon and low copper content which reduce galvanic potential versus chloride-rich environments. Protective oxide forms readily, and the alloy resists uniform thinning under typical outdoor exposure conditions.

Marine environments introduce pitting and crevice corrosion risks, particularly in stagnation zones or where chlorides concentrate. The alloy is more resistant than Cu-bearing alloys but requires surface treatments or sacrificial coatings for long-term immersion or splash-zone service.

Stress corrosion cracking susceptibility is low compared with high-strength 2xxx or 7xxx series alloys, due to modest residual stresses and limited copper and zinc content. However, welded assemblies with tensile residual stresses and metallurgical heterogeneity should be designed and processed carefully to minimize SCC risk.

Galvanic interactions should be considered when mating 4028 to more noble metals such as stainless steel or copper; isolation or sacrificial anodes can mitigate accelerated corrosion. Compared with 5xxx-series (Mg-rich) alloys, 4028 generally offers better weldability and similar atmospheric corrosion resistance but may be slightly more susceptible to localized chloride pitting.

Fabrication Properties

Weldability

4028 welds exceptionally well with standard fusion processes such as TIG and MIG, and is readily joinable with Al-Si filler alloys (e.g., ER4043 or ER4047). Hot-cracking tendency is low because silicon reduces solidification range, but improper filler selection or poor joint design can still yield porosity and HAZ softening. Heat input must be managed to limit HAZ over-aging or loss of mechanical properties adjacent to the weld.

Machinability

The alloy has moderate to good machinability in the annealed condition, with performance improving when small amounts of lead-free machinability-enhancers are present in some commercial variants. Carbide tooling with positive rake and adequate coolant delivers consistent chip control and surface finish. Recommended cutting speeds are moderate; increased feed rates reduce built-up edge but may increase surface roughness if not optimized.

Formability

Formability is excellent in O temper, enabling complex stamping, deep drawing and hydroforming operations with tight radii. As strength increases with H- and T-tempers, minimum bend radii and springback increase; T6 parts typically require larger flanges and radius allowances. For incremental forming operations, pre-aging in T4 followed by final aging can be used to balance formability and final properties.

Heat Treatment Behavior

4028 is semi-heat-treatable: controlled solution heat treatment followed by rapid quench and artificial aging produces a meaningful increase in strength. Solution treatment is typically performed between 510–540 °C depending on section thickness to dissolve soluble phases, followed by water quench to retain a supersaturated solid solution.

Artificial aging is commonly carried out at 160–190 °C for 4–10 hours to precipitate fine Mg-Si clusters and Si dispersoids; aging curves are section-sensitive and overaging will reduce strength and improve ductility. T5 (cooled from elevated temperature and artificially aged) is a production-friendly option when full solution treatment is impractical.

For shop-level tempering and annealing, O temper is achieved by heating to ~370–400 °C for stress relief or softening followed by controlled furnace cooling. Work hardening remains an effective method for strengthening where heat treatment is not available, particularly in H-series tempers.

High-Temperature Performance

Operational strength begins to decline above approximately 120–150 °C as precipitate stability decreases and dislocation-precipitate interactions weaken. For continuous service, designers typically limit 4028 to below 150 °C to retain a substantial fraction of room-temperature strength.

Oxidation resistance is similar to other Al alloys; protective oxide scales form rapidly and limit further high-temperature degradation under non-aggressive atmospheres. Extended exposure above 200 °C accelerates coarsening of strengthening phases and can cause permanent softening and dimensional change, particularly in thin sections where creep may become significant.

Weld HAZs are particularly susceptible to strength loss when exposed to elevated temperatures post-welding; appropriate post-weld aging or solution plus aging may be specified to recover properties depending on design requirements.

Applications

Industry	Example Component	Why 4028 Is Used
Automotive	Inner body panels, mounting brackets	Good formability in O and higher strength in T5/T6 for joined structures
Marine	Brackets, housings, trim	Reasonable chloride resistance and excellent weldability with Al-Si fillers
Aerospace	Secondary fittings, ductwork	Favorable strength-to-weight and good extrudability for complex profiles
Electronics	Heat sinks, housings	Sufficient thermal conductivity and dimensional stability after aging

4028 is often specified where manufacturability and weldability intersect with a need for higher mechanical performance than mild wrought alloys can provide. Its balanced properties permit use across several transport and industrial sectors where moderate strengths, good corrosion behavior and ease of fabrication are simultaneously required.

Selection Insights

Choose 4028 when designs require better strength than commercially pure aluminum (1100) while retaining substantial formability and superior weldability. Versus 1100, 4028 sacrifices some electrical and thermal conductivity but gains substantial tensile and yield strength.

Compared with common work-hardened alloys such as 3003 or 5052, 4028 provides higher strength in aged conditions and comparable atmospheric corrosion resistance, though it may be slightly less damage-tolerant in very aggressive chloride environments. Versus typical heat-treatable alloys like 6061/6063, 4028 offers improved weldability and silicon-informed extrusion/forming behavior at the expense of maximum achievable peak strength.

For procurement, prioritize 4028 when fabrication workflows include fusion welding with Al-Si filler alloys, when extrusion surface quality is key, or when a semi-heat-treatable alloy simplifies production without requiring the highest-strength heat-treatment cycles.

Closing Summary

Alloy 4028 occupies a practical niche among aluminum alloys by combining silicon-aided manufacture with controlled magnesium additions to produce a semi-heat-treatable material that balances formability, weldability, corrosion resistance and moderate-high strength. It remains relevant where designers require reliable manufacturability and service performance without the cost or SCC concerns associated with higher-strength, copper-bearing or zinc-rich alloys.