Aluminum A360: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

A360 is an aluminum alloy predominantly used in cast and wrought forms and is commonly categorized within the family of silicon‑bearing Al‑Si‑Mg alloys. Its chemistry centers on silicon and magnesium as the principal alloying additions that enable precipitation hardening and castability. The alloy is heat‑treatable, gaining strength through solution treatment, quenching and artificial aging rather than by cold work. Key traits include good castability, a favorable strength‑to‑weight ratio, decent corrosion resistance in many environments, and acceptable weldability when appropriate filler metals and techniques are used.

Industries that most commonly specify A360 include automotive (transmission and housing castings), consumer appliance housings, industrial components, and marine hardware where a combination of castability and reasonable mechanical performance is required. Designers select A360 for parts that require complex geometry produced economically by casting while still benefiting from post‑casting heat treatment to raise strength. Compared with higher‑strength wrought alloys, A360 offers lower cost and better castability; compared with pure Al, it trades conductivity and formability for far higher strength after aging.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, maximum ductility after solutionizing and slow cooling
T4	Medium	High	Good	Good	Solution heat treated and naturally aged; retains good formability
T5	Medium‑High	Moderate	Fair	Good	Cooled from casting and artificially aged; used for castings directly from mold
T6	High	Moderate‑Low	Limited	Good	Solution heat treated and artificially aged to peak strength
T651	High	Moderate‑Low	Limited	Good	T6 with stress‑relief by stretching; used where distortion control is required
Hxx (e.g., H14)	Medium	Reduced	Limited	Good	Strain‑hardened and partially annealed versions for wrought forms where applicable

Tempers modify A360’s balance of strength and ductility predictably: annealed (O) condition gives maximum elongation for forming while T6/T651 produces higher yield and tensile strengths at the cost of reduced formability. For cast components, T5 and T6 are the most common production tempers because they allow casting, minimal post‑machining, and aging schedules that deliver usable mechanical performance without extensive forming.

Chemical Composition

Element	% Range	Notes
Si	6.5 – 9.5	Primary alloying element improving fluidity, castability and strength after aging
Fe	0.2 – 0.8	Impurity that forms intermetallics; controlled to limit brittleness
Mn	≤ 0.5	Added to control grain structure and limit detrimental Fe phases
Mg	0.2 – 0.6	Enables Mg2Si precipitation hardening and contributes to strength
Cu	≤ 0.3	Small additions may increase strength but lower corrosion resistance
Zn	≤ 0.2	Usually low; excessive Zn is avoided to limit hot‑cracking and SCC risk
Cr	≤ 0.25	Controls grain structure and recrystallization in certain tempers
Ti	≤ 0.2	Grain refiner in cast and wrought production to refine primary structure
Others	Balance Al; trace elements controlled	Traces of Ni, V or Sr may be present for eutectic modification or property tuning

Silicon provides the matrix for Al‑Si eutectic structures that make A360 very castable and dimensionally stable. Magnesium combines with silicon to form Mg2Si precipitates during artificial aging, which is the principal strengthening mechanism. Minor elements and impurities influence grain size, cast‑structure morphology and secondary phase precipitation, which in turn control toughness, machinability and susceptibility to intergranular defects.

Mechanical Properties

A360 displays classical precipitation‑hardenable behavior: low strength in the annealed state and increasing strength after solutionizing and artificial aging. In T6 conditions the alloy achieves its design tensile properties as Mg2Si precipitates form and hinder dislocation motion. Yield and ultimate tensile strength scale with section thickness and cooling rate; thinner sections that quench faster typically reach higher strengths.

Ductility (elongation to failure) decreases with increasing temper and with increasing silicon content due to the presence of hard eutectic silicon particles. Hardness follows the same trend as tensile strength and is commonly measured by Brinell or Rockwell scales in castings to confirm aging condition. Fatigue performance is sensitive to casting porosity, surface finish and thermal history; porosity acts as a primary fatigue crack initiation site and reduces endurance limits substantially in as‑cast conditions.

Property	O/Annealed	Key Temper (e.g., T6)	Notes
Tensile Strength	120 – 180 MPa	250 – 360 MPa	Values vary with section thickness, porosity and exact composition
Yield Strength	60 – 120 MPa	170 – 260 MPa	Yield shows pronounced dependence on Mg content and aging schedule
Elongation	10 – 25%	4 – 12%	Elongation drops as aging progresses and as silicon particle size increases
Hardness	40 – 60 HB	80 – 120 HB	Hardness correlates with precipitate density and eutectic silicon morphology

Physical Properties

Property	Value	Notes
Density	~2.68 g/cm³	Typical density for Al‑Si alloys; depends slightly on alloying additions
Melting Range	~575 – 655 °C	Eutectic and α‑Al liquidus/solidus spread due to Si content
Thermal Conductivity	~120 – 150 W/(m·K)	Lower than pure Al because of Si and secondary phases
Electrical Conductivity	~30 – 45 %IACS	Reduced from pure aluminum by alloying; varies with temper
Specific Heat	~0.88 – 0.92 J/(g·K)	Close to that of pure aluminum
Thermal Expansion	~21 – 24 ×10⁻⁶ /K	Relatively high CTE; consider in thermal cycle assemblies

A360’s density and specific heat are close to those of many aluminum alloys, making it attractive where low mass and reasonable thermal storage are needed. The thermal conductivity is adequate for many thermal management applications, but silicon particles and intermetallics reduce conductivity relative to pure aluminum or highly conductive wrought alloys. The melting range and solidification behavior are directly related to silicon content and eutectic composition, which affect casting shrinkage and feeding requirements.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5 – 6 mm (limited)	Lower due to processing limitations	O, T4	Wrought sheet in A360 is less common; thin gauge possible after rolling
Plate	6 – 50 mm	Strength lower in thicker sections due to slower cooling	O, T5, T6	Thick cast plates require careful heat treatment to avoid soft core
Extrusion	Sections up to 200 mm	Strength depends on profile wall thickness and quench	T4, T6	Extruded product less common; A360 is more typically cast or die‑cast
Tube	Diameters typical for casting	Variable	O, T6	Cast tubular forms used for housings, not structural seamless tubing
Bar/Rod	Variable	Good strength after aging	T6	Bar stock may be produced for small machined components

Processing route has a major impact on mechanical performance. Cast forms of A360 benefit from mold design, rapid solidification and controlled porosity to achieve consistency, while wrought forms require rolling or extrusion followed by solution heat treatment and aging. Designers must match intended product form to manufacturing capabilities; thin, complex castings exploit A360’s fluidity while larger, thick sections require special heat‑treat and quench strategies.

Equivalent Grades

Standard	Grade	Region	Notes
AA	A360	USA	Aluminum Association designation for the alloy family
EN AW	AC‑42100 / AlSi9Mg?	Europe	Close equivalents may be in the AlSi9Mg family depending on exact chemistry
JIS	ADC9/ ADC12 variant	Japan	Japanese casting grades with similar Si‑Mg balance are used as functional equivalents
GB/T	ZL102 / AlSi9Mg?	China	Chinese casting standards include AlSi9Mg grades with comparable properties

Direct one‑to‑one equivalents depend on the precise composition, especially Mg and Cu content, and on whether the application expects a casting or wrought product. European EN designations and Chinese GB/T names are commonly matched by silicon and magnesium content ranges and by specifying mechanical property targets rather than relying solely on nominal alloy labels.

Corrosion Resistance

A360 exhibits good general atmospheric corrosion resistance typical of Al‑Si‑Mg alloys when properly finished and coated. The presence of silicon in the microstructure does not significantly impair the natural protective alumina film, but exposed interdendritic phases and casting porosity can create local anodic sites. Surface preparation and sealing of porosity are important for long‑term atmospheric durability.

In marine and chloride environments A360 performs reasonably but is more susceptible to localized corrosion than Al‑Mg wrought alloys with higher Mg content, such as 5052. Stress corrosion cracking is not a prominent failure mode for A360 under typical service conditions; however, galvanic coupling to more noble materials (stainless steel, copper) can accelerate localized attack at contact points. Protective coatings, anodizing or cathodic design practices mitigate these risks.

Compared with 6xxx series wrought alloys, A360 often has similar or slightly lower corrosion resistance depending on Cu impurity and porosity. Castings should be designed to avoid crevice geometries and to minimize porosity exposure to aggressive environments.

Fabrication Properties

Weldability

A360 can be welded by common processes (MIG/GMAW, TIG/GTAW) but attention must be paid to filler selection and heat input. Al‑Si fillers such as ER4043 (Al‑Si) are the typical choice to match base metal silicon content and to reduce hot‑cracking risk. Hot cracking is possible in thick sections or where high silicon promotes low‑melting eutectics; preheating and controlled heat input reduce residual stresses and cracking.

Machinability

Machinability of A360 is generally good relative to other aluminum casting alloys due to silicon providing abrasion resistance and chip control. Carbide tooling with positive rake, rigid setups and moderate cutting speeds produce the best surface finishes. Silicon particles wear tools faster than soft pure Al, so tool life considerations and coolant application are important in high‑volume machining.

Formability

Forming of A360 in wrought product is limited compared with low‑alloy, highly ductile grades. The O and T4 tempers offer the best cold formability and are preferred where bending or drawing is required. For cast components, forming is constrained to small adjustments; designers should favor net‑shape casting and minimal post‑cast forming.

Heat Treatment Behavior

A360 is heat‑treatable via the Al‑Si‑Mg precipitation hardening path. Solution treatment is typically performed near the solidus boundary but below incipient melting, commonly in the range of 520–540 °C, held to dissolve Mg2Si and homogenize microstructure. Rapid quench follows solutionizing to retain supersaturation of Mg and Si in the matrix.

Artificial aging (T6) is performed at temperatures from roughly 150–185 °C for times optimized to reach peak hardness and tensile properties. Overaging reduces strength and increases ductility while improving thermal stability. T temper transitions (e.g., T5 to T6) alter precipitate size and distribution; designers select temper based on balance of strength, distortion control and machinability.

If used in non‑heat‑treatable manner, A360 can be annealed (O) for maximum ductility. Work hardening provides limited strengthening; however, precipitation hardening remains the principal route to high strength for this alloy class.

High-Temperature Performance

A360 shows meaningful strength degradation with increasing temperature and is generally limited to continuous service below roughly 150 °C for load‑bearing applications. Above this range, precipitate coarsening and overaging reduce yield and tensile strengths and lower creep resistance. Short excursions to higher temperatures are tolerated but repeated thermal cycling accelerates microstructural evolution.

Oxidation in air is limited by the protective alumina film, but prolonged exposure at elevated temperature can alter surface oxide chemistry and reduce fatigue resistance through microstructural coarsening. Heat‑affected zones from welding exhibit localized softening if base metal is in a peak aged condition; post‑weld solution and aging or appropriate filler selection can restore acceptable properties.

Applications

Industry	Example Component	Why A360 Is Used
Automotive	Transmission housings, pump housings	Excellent castability, good strength after aging, cost effective for complex geometry
Marine	Small structural castings, brackets	Reasonable corrosion resistance and low density for weight‑sensitive parts
Aerospace	Non‑critical fittings, housings	Favorable strength‑to‑weight and ease of casting complex shapes
Electronics	Enclosures and heat spreader housings	Good thermal conductivity and dimensional accuracy from casting
Consumer Appliances	Motor housings, pump bodies	Low cost, good cast surface finish and adequate mechanical performance

A360 is used where a combination of economy, castability and adequate mechanical strength are required. It is especially favored for intricate cast geometries that would be expensive or impractical to manufacture in higher‑strength wrought alloys.

Selection Insights

Choose A360 when you require a castable aluminum alloy that can be aged to useful strengths while maintaining good dimensional control and acceptable corrosion resistance. It is a practical choice for complex, net‑shape components produced in moderate to high volumes.

Compared with commercially pure aluminum (1100), A360 trades some electrical and thermal conductivity and ease of forming for substantially higher tensile and yield strength after aging. Against work‑hardened alloys such as 3003 or 5052, A360 offers higher achievable strengths through heat treatment but generally less ductility and different corrosion behavior due to silicon and casting porosity. Versus common heat‑treatable wrought alloys like 6061, A360 may have lower peak strength but wins on casting economy and complex shape production where machining and fabrication costs would otherwise be prohibitive.

Closing Summary

A360 remains a relevant engineering alloy because it blends excellent castability with precipitation‑hardening capability to deliver an economical mix of strength, dimensional precision and corrosion performance. Its combination of properties makes it especially valuable for cost‑sensitive, geometrically complex components across automotive, marine and consumer applications.