Aluminum AlSi10: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

AlSi10 is a cast aluminum-silicon alloy belonging to the Al-Si family, commonly referenced as an Al-Si hypoeutectic to near-eutectic composition with approximately 10 wt% silicon. It is typically classified within cast alloy standards rather than the wrought 1xxx–7xxx series; common cataloguing uses EN AC-AlSi10 or regional casting equivalents rather than AA 2xxx/6xxx wrought designations.

The dominant alloying element is silicon, which controls the solidification behavior, fluidity, and wear characteristics; minor additions of Fe, Cu, Mn, Mg, Ti and trace elements tune strength, castability and heat-treatment response. Strengthening is a mixture of as-cast microstructure control (eutectic Si particles and Al matrix morphology), with the potential for precipitation hardening if sufficient Mg is present (e.g., AlSi10Mg variants) and appropriate solution + aging cycles are applied.

Key traits of AlSi10 include excellent castability and low shrinkage, good thermal conductivity among aluminum alloys, moderate-to-good corrosion resistance in many environments, and generally good weldability in many forms when porosity is controlled. It is widely used in automotive, tooling, low-pressure and high-pressure die casting, additive manufacturing (SLM/EBM) and consumer products where a balance of casting fidelity, dimensional stability and reasonable mechanical performance is needed.

Engineers choose AlSi10 where fluidity, thin-wall casting capability, thermal management and low casting defects are priorities, or where additive-manufactured parts require a silicon-rich matrix for thermal stability and minimal distortion. It is selected over higher-strength wrought alloys when complex near-net-shape cast geometries, lower tooling costs, or improved thermal behavior outweigh requirements for peak tensile strength or extensive forming.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O (Annealed)	Low	High	Excellent	Excellent	Stress-relieved, softest condition for heat treatable variants
As-cast	Low–Moderate	Low–Moderate	Limited	Good (with control)	Typical delivery condition from casting; microstructure dependent
T5 (Artificially aged after cooling)	Moderate	Low	Limited	Good	Common for castings and AM parts to gain strength without full solutioning
T6 (Solution treated + artificially aged)	High	Low–Moderate	Poor	Good	Applies mainly when Mg is present; significant strength increase
T7 (Overaged / stabilized)	Moderate	Moderate	Limited	Good	Improves dimensional stability and toughness at cost of some strength

The temper state strongly modifies the balance between strength and ductility for AlSi10, with T6-like treatments (where Mg is available) raising yield and ultimate strengths at the expense of elongation. As-cast microstructure, cooling rate and subsequent thermal treatment (or lack thereof) are the primary levers to tune performance; the presence and amount of Mg determine how effectively precipitation hardening can be used.

Chemical Composition

Element	% Range	Notes
Si	9.0 – 11.0	Primary alloying element controlling eutectic fraction, fluidity, thermal conductivity
Fe	0.2 – 0.8	Impurity that forms intermetallics (β-Al5FeSi) that can reduce ductility
Mn	0.05 – 0.45	Controls Fe-intermetallic morphology when present in small amounts
Mg	0.0 – 0.45	If present (>0.2) enables precipitation hardening (T6 response)
Cu	0.02 – 0.3	Raises strength but can reduce corrosion resistance if high
Zn	0.02 – 0.2	Minor; typically kept low to avoid deleterious effects
Cr	0.01 – 0.2	Grain structure modifier in some specifications
Ti	0.01 – 0.2	Grain refiner for castings and ingot metallurgy
Others	Balance Al; trace residuals	Residual impurities (Ni, Co, Pb) kept to minimum by spec

Silicon dictates microstructure (eutectic Si particle size, morphology and distribution) and directly affects casting behavior, wear resistance and thermal properties. Iron and manganese influence brittle intermetallic formation; controlled levels and modification (e.g., Sr for Si modification) improve ductility and machinability. Magnesium presence converts AlSi10 into a heat-treatable variant (AlSi10Mg), where solution treatment and aging enable much higher strengths via Mg2Si precipitation.

Mechanical Properties

Tensile behavior of AlSi10 depends strongly on casting method, section thickness and heat treatment. As-cast material typically exhibits a ductile-to-brittle balance controlled by the size and morphology of eutectic silicon and porosity; T6-treated AlSi10Mg variants gain substantially in yield and ultimate strength but lose some elongation. Fatigue performance is limited by casting defects and surface condition; the presence of porosity, shrinkage cavities or coarse Fe-intermetallics drastically reduces fatigue life relative to wrought alloys.

Yield strength in as-cast conditions is moderate and very section-sensitive; thinner sections cooled faster and generally show higher yield and tensile strength. Hardness ranges reflect the temper: annealed/as-cast conditions yield low hardness, while T5/T6 artificial aging increases hardness significantly. Surface treatments, hot isostatic pressing (HIP) or machining to remove near-surface defects improve fatigue and cyclic strain tolerance.

Property	O/Annealed	Key Temper (e.g., T6)	Notes
Tensile Strength (UTS)	120 – 200 MPa	240 – 320 MPa (AlSi10Mg T6)	Wide ranges due to casting method, section size, porosity and Mg content
Yield Strength (0.2% proof)	60 – 130 MPa	150 – 250 MPa	T6 markedly increases yield; as-cast yield is section-dependent
Elongation (A%)	3 – 12%	2 – 8%	Ductility lower in T6; better in annealed/as-cast when microstructure is fine
Hardness (HB)	40 – 80 HB	70 – 120 HB	Hardness correlates with degree of precipitation hardening and Si morphology

Physical Properties

Property	Value	Notes
Density	2.68 g/cm³	Typical for Al–Si cast alloys; slightly higher than pure Al due to Si content
Melting Range	~577 – 640 °C	Eutectic-related solidification begins near 577 °C; melting range depends on local composition
Thermal Conductivity	~120 – 150 W/m·K	Lower than pure Al; Si particles reduce conductivity but still good for heat sinks/thermal parts
Electrical Conductivity	~30 – 38 % IACS	Reduced compared with pure Al; useful for electrically conductive cast components but not as conductor-grade
Specific Heat	~0.90 J/g·K (900 J/kg·K)	Typical aluminum specific heat near room temperature
Thermal Expansion	22 – 24 µm/m·K	Coefficient of thermal expansion similar to other aluminum alloys; consider Si content for composite behavior

AlSi10 retains useful thermal conductivity and low density advantages of aluminum while the silicon content lowers conductivity compared with pure aluminum but improves thermal stability and wear. The melting/solidification behavior—eutectic reactions—governs casting practice and influences microstructure control strategies such as modification and grain refinement. Electrical conductivity is sufficient for many ancillary conductive applications but not competitive with high-purity aluminum for power transmission.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	Rare; limited thin castings	As-cast or aged behavior	As-cast / T5	Thin-walled cast sheet possible by pressure die-casting or AM; not common as rolled product
Plate	2 – 200 mm (cast)	Section-sensitive; thicker sections lower strength	As-cast / T6 (if Mg present)	Sand and permanent-mold plates used for structural castings
Extrusion	Limited	Not typical; wrought extrusions available only in special alloys	N/A	AlSi10 is primarily a casting alloy; extrusions use other alloys like 6063
Tube	Cast or die-cast sections	Depends on casting technique	As-cast / T5	Cast thin-walled tubing achievable by die or investment casting; AM allows complex channels
Bar/Rod	Cast bars or ingots	Used for feedstock and forging	As-cast	Often remelted or further processed for specific manufacturing routes

AlSi10 is predominantly supplied and used in casting forms: sand, die, permanent-mold, investment casting and increasingly as powder for additive manufacturing. Mechanical property and defect sensitivity vary greatly between those product forms because cooling rates differ; die-cast and AM parts cool faster and produce finer microstructures, giving higher as-built strengths. Wrought forms (extrusions/rolled plate) are uncommon; designers should prefer other wrought alloys if extensive cold forming is required.

Equivalent Grades

Standard	Grade	Region	Notes
EN	AC-AlSi10	Europe	Standard casting designation for near-10% Si cast aluminium
AA / ASTM	AlSi10 (approx.)	USA	Not an exact AA designation; A356 and A357 are similar low-Si variants with Mg
JIS	ADC10 (approximate)	Japan	ADC10 and ADC12 are die-casting alloys with similar Si content but different Cu/Mg levels
GB/T	AlSi10	China	Chinese standards list AlSi10 casting grades with comparable composition windows

Equivalents are approximate because regional standards tune trace elements and allowable impurities for specific casting processes (die casting versus sand casting). ADC-series die-cast alloys and EN AC-AlSi10 are close in Si content but may differ in Cu or Mg levels; these differences alter heat-treatability and corrosion behavior. Always consult the specific standard sheet for tensile and chemical limits when substituting between regional grades.

Corrosion Resistance

AlSi10 generally offers good atmospheric corrosion resistance due to the protective aluminum oxide film; silicon itself is inert and does not significantly accelerate uniform corrosion. Localized corrosion can occur where Fe-rich intermetallics and casting defects introduce micro-galvanic sites; surfaces with porosity or poor finishing are more susceptible to pitting, especially in chloride environments.

In marine or chloride-rich environments, AlSi10 behaves moderately well but is not as robust as 5xxx-series magnesium-bearing sacrificial alloys; chloride-induced pitting is the principal concern and protective coatings or anodizing are commonly applied. Stress corrosion cracking (SCC) susceptibility is low compared to high-strength Al-Zn-Mg alloys, but residual tensile stresses and corrosion pits can combine to initiate fatigue cracks; prudent design and post-casting treatments reduce risk.

Galvanic interactions follow typical aluminum behavior: AlSi10 will corrode anodically when in electrical contact with more noble metals such as stainless steel or copper in conductive electrolytes. Compared with wrought work-hardened 3xxx/5xxx series, AlSi10 trades some corrosion toughness for casting-specific benefits; compared with heat-treatable high-strength alloys (7xxx), AlSi10 is more corrosion-resistant and less prone to SCC but typically lower in peak mechanical strength.

Fabrication Properties

Weldability

Welding AlSi10 is feasible with TIG and MIG processes for repair or joining of castings, but porosity and hot-cracking remain primary concerns. Preheating to moderate temperatures, controlling hydrogen sources, and using appropriate filler alloys (commonly Al-Si-based fillers like ER4043 or AlSi5) reduce cracking and improve bead integrity. Heat-affected zone (HAZ) softening is generally limited compared with heavily age-hardenable alloys, but local changes in silicon morphology and porosity can affect mechanical performance of the weld region.

Machinability

AlSi10 machinability is moderate: the presence of hard eutectic silicon particles increases tool wear and promotes abrasive cutting conditions compared with pure aluminum. Carbide tooling with polished flutes, positive rake geometry, and coolant is recommended for reliable tool life and surface finish. Chip formation tends to be discontinuous; stable feeds and speeds that avoid built-up edge and minimize vibration improve surface integrity and dimensional control.

Formability

Cold forming of AlSi10 is very limited because it is a casting alloy with low ductility in most tempers; bending, deep drawing and stamping are typically impractical. Best forming approaches are near-net-shape casting, machining, or localized thermal forming on specially prepared cast blanks. When some deformation is required, softer annealed conditions and elevated-temperature forming methods may be used, but designers usually prefer other wrought alloys for extensive forming.

Heat Treatment Behavior

When Mg is present above threshold levels (AlSi10Mg), AlSi10 becomes responsive to classical heat treatment sequences: solution treatment at approximately 520–540 °C dissolves Mg-bearing phases and homogenizes the microstructure, followed by rapid quenching and artificial aging (typically 150–200 °C) to precipitate Mg2Si and achieve T6 or T5 strength levels. The silicon network and coarse eutectic particles limit the maximum achievable strength compared with Al-Mg-Si wrought alloys, but T6 treatment reliably improves both yield and UTS for cast and AM parts.

As-cast and non-heat-treatable variants rely on solidification microstructure and potential work-hardening for strength. Annealing cycles are used to relieve residual stresses and soften material for limited post-cast processing, typically via subcritical anneal or stress-relief treatments. Overaging (T7) is used to improve dimensional stability and toughness for components requiring service temperature resilience.

Solution and aging cycles must be carefully matched to casting section sizes and the presence of porosity; slow cooling or inadequate quench can leave coarse precipitates and reduce hardening response. Hot isostatic pressing (HIP) is often used prior to aging in high-integrity components to close internal porosity and improve fatigue resistance before final tempering.

High-Temperature Performance

AlSi10 shows progressive strength loss with increasing temperature; practical continuous-service limits are generally in the 100–150 °C range for structural applications, with short-term exposures up to ~200 °C possible depending on temper. The silicon-rich microstructure provides better dimensional stability at elevated temperature than many softer aluminum alloys, but precipitation-hardened strength (if present) will degrade with thermal exposure and overaging.

Oxidation in air is surface-limited due to the protective Al2O3 layer, so oxidation rates are small at common service temperatures, but prolonged exposure to elevated temperatures accelerates coarsening of the microstructure and softening. Heat-affected zone behavior during welding or local peak temperature excursions can show embrittlement or reduced ductility due to silicon coarsening and pore evolution.

Applications

Industry	Example Component	Why AlSi10 Is Used
Automotive	Engine brackets, intake manifolds, housings	Excellent castability, thin-wall capability, thermal performance
Marine	Non-structural housings, pump components	Good atmospheric corrosion resistance and castability for complex shapes
Aerospace	Brackets, ducts, low-load housings	Low density and dimensional stability for complex cast or AM geometries
Electronics	Heat sinks, thermal spreaders	Good thermal conductivity and ease of producing complex cooling channels
Additive Manufacturing / Tooling	Conformal-cooling inserts, prototypes	High fidelity in SLM/EBM, fine microstructure, post-heat-treatment response

AlSi10 is favored where complex, near-net-shape parts with thermal requirements and reasonable mechanical strength are required. Its wide adoption in additive manufacturing and die casting is driven by repeatable microstructure, good thermal behavior and the ability to produce lightweight components economically.

Selection Insights

For general selection, choose AlSi10 when castability, dimensional control and thermal conductivity are primary design drivers and when the part geometry favors near-net-shape production. Expect moderate static strength and limited formability; specify T6 (if AlSi10Mg variant) when higher strength is required and control of porosity is ensured for fatigue-critical parts.

Compared with commercially pure aluminum (1100), AlSi10 sacrifices some electrical and thermal conductivity and formability in exchange for substantially higher as-cast strength and much better castability. Compared with work-hardened alloys like 3003 or 5052, AlSi10 generally provides higher casting-specific strength and easier complex-shape production at the cost of limited cold forming and variable corrosion tolerance in aggressive chloride environments. Compared with heat-treatable wrought alloys such as 6061/6063, AlSi10 (especially non-Mg variants) may offer lower peak tensile strengths but superior casting capability and thermal behavior, making it the preferred choice in cast or additive-manufactured components even if ultimate strength is lower.

Closing Summary

AlSi10 remains a relevant engineering alloy because it combines excellent castability and thermal performance with sufficient mechanical properties for many industrial applications, particularly in die casting and additive manufacturing. Its silicon-rich chemistry and adaptable processing (casting, heat treatment, HIP, AM) provide designers with a practical trade-off between manufacturability and in-service performance for lightweight, complex components.