Aluminum 380: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 380 (commonly specified as A380 in die-casting practice) is a cast aluminum-silicon-copper alloy that belongs to the aluminumsilicon casting families often referenced in the "3xx" casting group. It is formulated for high-volume pressure-die casting and foundry use, with a compositional emphasis on silicon for fluidity and copper for improved as-cast strength and elevated temperature stability.

The major alloying elements are silicon (for fluidity and eutectic strengthening), copper (for precipitation and elevated temperature strength), and controlled levels of iron, zinc, manganese, and trace titanium for grain refinement. The strengthening mechanisms are mixed: inherent as-cast microstructure and copper-containing intermetallics provide baseline strength, and limited heat treatment (T5/T6 style artificial aging) can develop additional strength through precipitation hardening.

Key traits of 380 include very good die-fill characteristics, good dimensional stability, attractive surface finish and machinability relative to many casting alloys, moderate corrosion resistance and reasonable mechanical properties for die-cast components. Its weldability is limited relative to wrought aluminum alloys and it is not aimed at extensive forming after casting. Typical industries include automotive, consumer electronics enclosures, electrical housings, mechanical housings and fittings where near-net shape, high-volume production and dimensional precision are prioritized.

Engineers select 380 when a combination of fast die-cast producibility, good as-cast strength, and economical cost are required versus alternative alloys. The alloy is chosen over higher-performance wrought alloys when complex geometry and low secondary machining are prioritized, and is chosen over lower-alloyed die-casting alloys when an elevated as-cast strength and thermal stability are needed without large increases in process complexity.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	Moderate (section-dependent)	Poor	Poor to Fair	As-cast, stress-relief anneal may be applied; highest ductility for cast condition
T5	Medium-High	Low–Moderate	Limited	Poor to Fair	Artificial aging after quench from casting or after rapid cooling; common for die-cast parts
T6	High	Low	Limited	Poor	Solution treat + artificial age can raise strength but requires careful porosity control
T651 (less common)	High	Low	Limited	Poor	Stress-relieved and artificially aged; used when dimensional stability after machining is critical
H14 (work-hardened; uncommon)	Medium	Low	Limited	Poor	Typically not applied to castings; referenced for comparative purposes

Selected tempers for 380 are often dictated by the casting process and part geometry rather than conventional wrought tempering routes. T5 is the most commonly used industrial temper because it raises strength through artificial aging without the extensive thermal exposure and distortion risks of full solution treatment.

Applying full solution treatment and T6 aging is possible and can improve mechanical properties but requires careful control of porosity, hydrogen content and distortion; many die-cast shops therefore prefer T5 or as-cast conditions to balance performance, cost and dimensional stability.

Chemical Composition

Element	% Range	Notes
Si	7.5 – 10.5	Primary alloying element; improves fluidity, reduces shrinkage, forms eutectic silicon network
Fe	0.6 – 1.3	Impurity element that forms intermetallics (Fe-rich) which reduce ductility if high
Mn	0.0 – 0.5	Controls intermetallic morphology; small additions improve strength and castability
Mg	0.05 – 0.35	Low levels; limited role in precipitation strengthening for 380
Cu	2.5 – 4.5	Major strengthening element; promotes precipitation phases and higher elevated-temperature strength
Zn	0.5 – 1.2	Minor strengthening contribution; affects corrosion behaviour if elevated
Cr	0.05 – 0.25	Helps control grain and intermetallics; limits cracking in some conditions
Ti	0.01 – 0.25	Grain refiner for improved die filling and finer microstructure
Others (Ni, Pb, Sn, B)	trace – specified max	Typically controlled at low levels; lead and tin sometimes controlled for machinability; Al balance

The performance of 380 is strongly controlled by the Si–Cu balance and by trace elements that influence intermetallic chemistry and morphology. Silicon promotes a fine eutectic that aids castability and dimensional control, while copper supplies precipitation or intermetallic strengthening that increases hardness and tensile properties. Controlled iron and manganese content are critical to avoid coarse brittle intermetallics that would reduce ductility and fatigue life.

Mechanical Properties

380 displays as-cast tensile and yield behavior that is strongly section-thickness dependent because of solidification microstructures, porosity and the distribution of eutectic silicon and Cu-rich intermetallics. Typical as-cast strength is adequate for many structural components, but elongation remains modest and impacted by porosity and casting defects. Fatigue performance is limited by surface quality, casting defects and the presence of brittle intermetallics; shot-blasting, surface machining, and design for reduced stress concentration are common mitigation strategies.

Under artificial aging (T5) and especially under controlled solution treatment plus aging (T6), the Cu-bearing phases can develop precipitation strengthening that increases both yield and UTS, at the cost of reduced ductility. Hardness follows the same trend and is often used as a quick production control metric for temper response. Thickness and cooling rate have a first-order effect: thin sections cool faster, producing finer microstructures and higher as-cast strengths but also higher residual stresses.

Property	O/Annealed	Key Temper (e.g., T5/T6)	Notes
Tensile Strength (UTS)	180 – 260 MPa	240 – 360 MPa	Wide range depending on section, porosity and heat treatment; typical T5 ~250–320 MPa
Yield Strength (0.2% offset)	90 – 170 MPa	160 – 260 MPa	Yield increases significantly after aging; design should use conservative lower bounds for thin-walled castings
Elongation (A5)	1 – 8%	1 – 5%	Elongation is low compared with wrought alloys and strongly dependent on porosity and section thickness
Hardness (HB)	60 – 90 HB	85 – 120 HB	Brinell hardness used for process control; hardness correlates with UTS for typical tempers

Physical Properties

Property	Value	Notes
Density	2.75 – 2.82 g/cm³	Slightly higher than pure aluminium due to Si and Cu content
Melting Range	~500 – 640 °C	Eutectic and solidus/liquidus range is alloy-dependent; start of flow is lowered by Si
Thermal Conductivity	110 – 140 W/(m·K)	Lower than pure Al; depends on alloying and microstructure
Electrical Conductivity	~20 – 35 %IACS	Copper and silicon reduce electrical conductivity compared with pure Al
Specific Heat	~880 – 900 J/(kg·K)	Close to other Al-Si casting alloys
Thermal Expansion	21 – 24 µm/(m·K)	Moderate thermal expansion typical for Al-Si alloys; design for differential expansion with other materials

The physical properties reinforce typical die-casting use: the density is favorable for weight-sensitive components, thermal conductivity is adequate for many housings and heat-spreading uses but lower than pure Al. The melting and solidification behavior dominated by silicon is the key to excellent die-fill and low shrinkage, while electrical conductivity is a secondary consideration and typically sacrificed to achieve better mechanical and casting properties.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Die-castings (components)	Wall thickness 1–10 mm	As-cast strength; thin sections stronger due to faster cooling	O, T5, T6 (less common)	Primary product form; best surface finish and dimensional control
Permanent-mold castings	5–40 mm	Lower cooling rates, coarser microstructure	O, T5	Used for larger parts where die casting not economical
Sand castings / gravity	5–100+ mm	Coarser microstructure, lower strength	O	Less common for 380; used when geometry or volumes dictate
Bar / Forging Stock	Limited; specialty	Not typical	—	380 is rarely used as wrought product; bars may be used for experimental work
Extrusion / Sheet / Plate	Not standard	Not applicable	—	380 is generally not produced as sheet/plate or standard extrusion stock; use wrought alloys instead

Die-casting is the dominant processing route for 380 and that dictates the product forms available and the design rules used by engineers. Wall thickness, gate location, cooling rate and die design are primary lever arms for controlling properties, and the alloy is optimized around the production realities of high-pressure die-casting. When designers require sheet, plate or extruded forms they typically switch to wrought alloys because 380 is not commonly produced in those product forms.

Equivalent Grades

Standard	Grade	Region	Notes
AA	380 / A380	USA / International	Common die-casting designation in North America and by several foundry standards
EN AW	AlSi9Cu3(Fe)	Europe	Close equivalent in European casting standards; nomenclature emphasizes nominal Si and Cu content
JIS	ADC12	Japan	Widely used Japanese die-casting alloy that is similar to A380 in composition and application
GB/T	AlSi9Cu3 / ZL104	China	Chinese casting standards list similar Al–Si–Cu grades often used as A380 substitutes

Equivalency is approximate because foundry practice allows variation in Fe, Mn and trace additions that materially affect castability and mechanical response. Specifications differ on acceptable impurity levels, heat treatment response and required testing, so engineers should check the exact composition and mechanical property tables before accepting an alternative grade for critical applications.

Corrosion Resistance

Alloy 380 exhibits moderate general atmospheric corrosion resistance characteristic of Al-Si alloys, with protection provided by the passive aluminum oxide film. Copper in the alloy tends to reduce pitting resistance and can promote localized corrosion in chloride-rich environments, which necessitates coatings, anodizing alternatives or design allowances in marine or aggressive atmospheres. Protective coatings, sealants and cathodic protection strategies are commonly applied on critical parts used in coastal or high-humidity environments.

Stress corrosion cracking is less common in Al-Si casting alloys than in high-strength wrought aluminum-copper or high-strength 7xxx series alloys, but susceptibility can increase with elevated copper content, tensile residual stress and certain service environments. Galvanic interactions are important in assembly design: when 380 is coupled to steels, stainless steels or copper alloys, designers must account for galvanic series differences and often isolate the aluminum or use sacrificial anodes, especially where coatings are breached. Compared with Mg-rich Al-Mg alloys (such as 5052), 380 is more prone to localized corrosion due to alloyed copper; however it has superior castability and often preferred for complex shapes where coatings can be reliably applied.

Fabrication Properties

Weldability

Welding of 380 is challenging because die-cast porosity, entrapped gases and the presence of silicon and copper-rich intermetallics promote hot cracking and poor weld integrity. Fusion welding (MIG/TIG) is possible on properly prepared and sectioned parts using Al-Si filler alloys such as ER4043 (Al-Si) to improve fluidity and reduce hot cracking tendency; ER5356 may be used where higher strength is needed but with increased risk of cracking. Preheating, careful cleaning of fluxes and machining back to sound metal are commonly required; welded joints generally do not match the parent material’s strength and fatigue life.

Machinability

380 is recognized for good machinability relative to many casting alloys because of the presence of silicon particles that produce short, broken chips and stabilize cutting. Carbide tooling with positive rake and good coolant is recommended, and medium-to-high cutting speeds are typical for semi-finish and finish operations. Tool life is improved by minimizing vibration, controlling cut depth and using coatings suited to aluminum machining; lead or tin-bearing variants may show even better machining performance but are less common due to environmental controls.

Formability

Forming 380 by cold bending, deep drawing or stamping is very limited because castings have low ductility and brittle intermetallics. Near-net-shape design is the dominant strategy: design the die and gating to produce the final geometry and minimize post-cast forming. Local machining, trimming and light bending of thin sections are possible but require temper selection (use of O/T5) and careful control of springback and cracking. When significant forming is required, engineers typically switch to wrought alloys specifically formulated for formability.

Heat Treatment Behavior

As a copper-containing, cast Al-Si alloy, 380 demonstrates a limited but useful response to heat treatment. Solution treatment is possible in the 510–540 °C range to dissolve soluble phases followed by rapid quenching; however, the effectiveness is limited by casting porosity, entrained gases and the stability of intermetallics that do not fully dissolve. Overlong solution treatments can lead to distortion or exacerbate porosity issues, so process windows are narrower than for wrought alloys.

Artificial aging (T5) at 150–220 °C is the most practical industrial route to increase strength for die-cast 380 because it does not require full solution treatment. T5 generates a moderate precipitation response of Cu-rich phases, improving yield and hardness without the geometric changes associated with full solution treatment. T6 (solution treat + artificial age) can provide higher peak strength but requires careful control and is less common due to cost, distortion and the risk of hydrogen porosity