Aluminum 383: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 383 (commonly referenced as A383 in die-casting nomenclature) is a cast aluminum-silicon-copper alloy that sits in the Al–Si–Cu casting family often catalogued in the 3xx.x casting series. Its chemistry is centered on a relatively high silicon content with intentional copper additions to raise strength and allow age hardening; the balance is aluminum with trace alloying agents tuned for castability.

Strengthening in 383 is primarily precipitation/age hardening driven by Cu and to a lesser extent Mg, combined with microstructural refinement obtained during solidification and heat treatment; this alloy is therefore classed as heat-treatable in common engineering practice for die-cast parts. Typical traits include good die-cast fluidity and dimensional stability, moderate to high static strength after aging, acceptable thermal conductivity, and reasonable corrosion resistance in atmospheric environments; formability is not a primary design driver because 383 is intended for cast geometries rather than sheet forming.

Industries that most commonly use 383 include automotive (structural housings, transmission and engine components), consumer electronics (structural housings and connectors), and some industrial equipment where complex thin-walled cast geometry with moderate strength is required. Engineers select 383 over other alloys when die-cast manufacturability, dimensional tolerance, and an ability to reach higher strength via post-cast heat treatment are prioritized over the ductility and surface finish of wrought products.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O (As-cast / Annealed)	Low	Higher (3–8% typical)	Poor to Fair	Fair	Stress-relieved / as-cast microstructure; highest ductility for cast parts
T5 (Artificially aged)	Medium	Lower (1–4%)	Poor	Fair–Poor	Common for die-castings aged directly after quench or slow cooling
T6 (Solution treated & artificially aged)	High	Low (1–3%)	Poor	Limited	Achieves peak strength via solutionizing, quenching and aging
T7 (Overaged / Stabilized)	Medium–High	Low–Moderate	Poor	Limited	Used to improve stability and toughness at modest loss of peak strength
HT (Special heat treatments)	Variable	Variable	Poor	Variable	Proprietary stabilizing cycles for dimensional or mechanical optimization

Temper selection has a major impact on 383 performance: T6 provides the highest static tensile properties at the expense of elongation, while T5 is a production-friendly compromise that avoids full solution heat treatment. The as-cast (O) condition retains the most ductility and reduces distortion risk but yields substantially lower strength and hardness compared with T5/T6 conditions.

Chemical Composition

Element	% Range	Notes
Si	8.5–11.5	Primary alloying element; controls fluidity, reduces shrinkage and modifies strength
Fe	0.6–1.5	Impurity element; forms intermetallics that can embrittle grain boundaries if high
Mn	0.2–0.6	Helps modify Fe-intermetallics and slightly improves strength and toughness
Mg	0.05–0.30	Contributes to precipitation hardening when combined with Cu; often low in cast grades
Cu	2.0–3.5	Principal strengthening addition for age hardening; increases strength and can reduce corrosion resistance
Zn	0.1–0.5	Minor; typically controlled to low values, influences strength marginally
Cr	0.05–0.25	Grain refiner and helps control intermetallic morphology
Ti	0.02–0.15	Used as grain refiner during melting and casting operations
Others (Ni, Pb, Sn, balance Al)	Trace	Small controlled additives or residuals; aluminum forms the balance of the alloy

The chemistry of 383 is optimized for castability and age hardening: silicon improves fluidity and reduces shrinkage, while copper provides a potent precipitation-strengthening mechanism. Iron and manganese control intermetallic phases and influence toughness; minor elements such as Ti and Cr are used to refine grains and improve feeding during solidification.

Mechanical Properties

The tensile behavior of 383 is strongly dependent on casting quality, section thickness, and temper. As-cast material typically shows moderate ultimate tensile strength with relatively low ductility attributable to porosity and coarse silicon particles; after T5/T6 heat treatments the alloy develops precipitates that increase yield and ultimate strengths but reduce elongation.

Yield strength scales with aging condition and section size: thin-walled die components respond faster to artificial aging and exhibit higher yields than thicker sections due to faster quench rates and finer microstructure. Hardness increases markedly from the O to the T6 condition, reflecting the precipitation of Cu-rich phases; Brinell hardness values move from relatively low (soft cast) to moderate-hard depending on heat treatment.

Fatigue resistance in 383 is poorer than wrought aluminum alloys because cast porosity and intermetallics act as crack initiation sites; design for fatigue requires controlled casting practice and often post-process densification or surface treatment. Thickness effects are pronounced — thicker sections cool slowly, coarsen eutectic silicon and intermetallics, and show reduced strength and fatigue life compared with thin-wall castings.

Property	O/Annealed	Key Temper (e.g., T6)	Notes
Tensile Strength (UTS)	120–200 MPa	260–350 MPa	Wide range due to section thickness, porosity and heat treatment
Yield Strength (0.2% offset)	70–140 MPa	180–300 MPa	T6 raises yield substantially via Cu precipitation
Elongation	3–8%	1–4%	Ductility falls with increasing strength and aging
Hardness (HB)	50–80 HB	80–110 HB	Brinell hardness increases with aging and reduced porosity

Physical Properties

Property	Value	Notes
Density	2.70–2.78 g/cm³	Typical for Al–Si casting alloys, slightly dependent on porosity
Melting Range	~515–615 °C (solidus–liquidus)	Eutectic and primary silicon influence melting interval; process control critical
Thermal Conductivity	~120–150 W/m·K	Lower than pure Al due to alloying; still good for heat dissipation
Electrical Conductivity	~20–35% IACS	Reduced by alloying elements especially Cu and Si
Specific Heat	~0.85–0.95 J/g·K	Typical aluminum specific heat; varies slightly with temperature
Thermal Expansion	21–24 µm/m·K	Coefficient of thermal expansion similar to many Al–Si cast alloys

The physical profile makes 383 attractive for components requiring good thermal dissipation with relatively low mass. Melting and solidification behaviour are central to die-casting process design because the eutectic structure and primary silicon morphology control mechanical properties and shrinkage tendencies.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Die-castings (primary)	Wall thickness 1–12 mm	Thin sections: higher strength after aging; thick sections: lower strength	O, T5, T6	Most common form for 383; complex geometries, thin walls
Sand/ permanent mold castings	>10 mm	Coarser microstructure, lower mechanical properties	O, HT	Used for larger parts where die casting is impractical
Ingot / Slab	Casting feedstock sizes	Not applicable	Raw as-cast	Provided to die-casters and foundries for remelting
Machined components	Varied after casting	Strength depends on parent casting and heat treatment	T5/T6	Post-cast machining is common for critical features
Forging/Extrusion	Rare	Not typically processed in extrusion/forging	N/A	Alloy chemistry and casting-focused design make extrusion uncommon

383 is primarily produced and consumed as die-cast components; any sheet, plate, or wrought processing is uncommon and typically avoided because the alloy is optimized for solidification-controlled properties. Design and processing must account for section thickness and gating to minimize porosity and ensure predictable mechanical performance in the finished casting.

Equivalent Grades

Standard	Grade	Region	Notes
AA	383 / A383.0	USA	Common aluminum association casting designation for Al–Si–Cu die-casting
EN AW	AlSi9Cu3(Fe) / similar	Europe	Typical EN equivalent nomenclature for similar chemical family
JIS	ADC12 (close equivalency)	Japan	ADC12 is commonly referenced as a counterpart to A383 in die-casting
GB/T	AlSi9Cu3 / similar	China	Chinese casting standards list comparable Al–Si–Cu alloys with similar properties

Equivalency is functional rather than exact; composition windows, impurity limits (particularly iron and lead), and permitted heat-treatment recipes can vary by region and standard. When substituting, engineers must reconcile differences in Cu and Si percentages, permissible impurities, and documented mechanical property ranges rather than relying on name equivalence alone.

Corrosion Resistance

In atmospheric conditions 383 shows reasonable resistance due to the formation of a protective aluminum oxide film; general corrosion rates are modest except where chloride-laden or acidic environments accelerate attack. Copper additions, while beneficial for strength, reduce the alloy’s resistance to localized corrosion, making parts containing high surface Cu content more susceptible to pitting in aggressive environments.

In marine or high-chloride environments, 383 is inferior to 5xxx series Al–Mg alloys because Cu promotes micro-galvanic sites and pitting; designers should consider coatings, anodizing, or cathodic protection where seawater exposure is expected. Stress corrosion cracking (SCC) is not a predominant failure mode for 383 compared with high-strength wrought alloys, but coarse intermetallics and casting defects can localize stresses and promote crack initiation under cyclic load with corrosive agents.

Galvanic interactions require attention: when mated to steel, stainless, or copper components, 383 will typically be anodic and corrode preferentially if in conductive electrolyte; mating metals and joint design, insulating barriers, or protective coatings are recommended. Compared with other alloy families, 383 balances castability and strength at the cost of somewhat reduced marine and pitting resistance when compared to Al–Mg series.

Fabrication Properties

Weldability

Welding of 383 is feasible but challenging; die-cast microstructure, porosity and high silicon content increase hot-cracking susceptibility and produce variable HAZ softening. TIG and MIG techniques can be used for repair or attachment but often require pre- and post-weld procedures such as substrate preparation, specialized filler alloys (Al‑Si fillers like 4043 are commonly used to match silicon content), and elimination of trapped gases. Extensive welding may degrade mechanical properties and introduce HAZ regions with lower strength than the parent T5/T6 condition; welding should be minimized on critical load-bearing sections.

Machinability

Machinability of cast 383 is generally good compared with many wrought alloys because the Al–Si microstructure produces short, brittle chips that are easy to break, and the alloy machines at moderate to high feed rates. Carbide tools with appropriate coatings are recommended for consistent tool life; coolant use helps control temperatures and chip evacuation in deep cavities. Surface finish can be affected by porosity and intermetallics; finishing operations often include vibration-free fixturing and conservative feeds to avoid tool chatter and built-in surface defects.

Formability

As a casting alloy, 383 is not designed for extensive cold forming; bend radii for any post-cast forming are typically large and constrained by localized porosity and intermetallics which reduce ductility. Best forming results occur in the as-cast annealed condition with minimal forming strains, or by designing cast geometry to net shape to avoid post-cast forming. Where limited forming is required, low-temperature warm forming combined with appropriate tool geometry can reduce cracking risk, but design for net-shape die-casting is the preferred route.

Heat Treatment Behavior

Heat treatment of 383 follows classical solution and aging sequences used for Al–Si–Cu cast alloys: solution treatment (typically in the range of 495–540 °C depending on section and spec) dissolves soluble phases and homogenizes the matrix, followed by rapid quenching to retain a supersaturated solid solution. Artificial aging (T5/T6) at temperatures between ~150–220 °C precipitates Cu- and Mg-containing phases that significantly raise yield and tensile strengths; aging cycles are tuned for a balance of strength and retained toughness.

T7 and overaging cycles are applied when dimensional stability and resistance to property deterioration during service or machining is required; overaging trades peak strength for improved resistance to softening during subsequent thermal exposure. For cast 383, achieving consistent solution treatment can be limited by section thickness and trapped porosity, so many production parts use T5 aging directly on the as-cast condition to gain stiffness without the distortion risks inherent in full solution treatment.

High-Temperature Performance

Mechanical strength of 383 degrades progressively with temperature; sustained service above ~120–150 °C leads to significant loss of aging precipitates and therefore reduced yield and ultimate strength. Oxidation at elevated temperatures is generally limited by the aluminum oxide film, but prolonged exposure and thermal cycling can change surface oxide characteristics and promote scale growth in aggressive atmospheres. The heat-affected zone adjacent to welds can experience localized softening and coarsened precipitates, reducing localized high-temperature strength and fatigue life.

For short-term elevated temperature excursions, carefully selected aging conditions and alloy stabilization can mitigate property loss, but 383 is not recommended for continuous high-temperature structural use; designers requiring sustained strength above ~150 °C should consider specialized high-temperature aluminum alloys or alternative materials.

Applications

Industry	Example Component	Why 383 Is Used
Automotive	Transmission housings, valve bodies	Die-castability, thin-wall dimension control, and post-cast strength
Consumer Electronics	Enclosures, structural frames	Good thermal conductivity, complex geometry, and economy in high-volume casts
Industrial Machinery	Pump housings, compressor covers	Corrosion resistance in neutral environments and casting geometry freedom
HVAC / Thermal Management	Heat sink housings, blower components	Thermal conductivity and ability to form integrated fins in one casting
Electrical Connectors	Connector housings	Dimensional stability, machinability for mating features

383 is typically specified where complex thin-walled cast geometry, reasonable mechanical strength after aging, and cost-effective high-volume production are required. The alloy’s balance of castability and post-cast strength makes it a frequent choice for housings and components that require integrated features and moderate mechanical loads.

Selection Insights

When selecting 383, engineers should favor applications requiring die-cast complex shapes and moderate to high post-aged strength while accepting lower ductility and some corrosion trade-offs. Compared with commercially pure aluminum (1100), 383 offers substantially higher strength and better dimensional stability but sacrifices electrical conductivity and formability due to alloying and casting-induced microstructure.

Against common work-hardened alloys such as 3003 or 5052, 383 provides significantly higher age-hardenable strength for cast parts but lags the marine corrosion resistance and sheet-form formability of the Mg-bearing wrought alloys. Compared with heat-treatable wrought alloys like 6061/6063, 383 can be preferred when net-shape casting and complex integrated geometry are the overriding priorities even though peak wrought strengths and fatigue resistance of 6xxx series may be superior for many structural wrought applications.

Closing Summary

Alloy 383 remains relevant where die-casting economics, thin-wall complexity, and the capacity for post-cast age hardening combine to meet component performance targets; its chemistry and process flexibility provide designers a practical compromise between castability, strength, and thermal performance. Proper selection of temper, control of casting conditions, and attention to surface protection extend its service life and make it a workhorse in automotive, electronics, and general industrial applications.