BS 1490 · Group A · General Purpose
lm6
Aluminium Alloy
Al-Si12 — The Best Castability in the LM Series
Sand Casting
Gravity Die Casting
Low Pressure Die Casting
High Pressure Die Casting
ISO 9001:2015
At a Glance
- Nominal composition
- Si content
- Density
- Best tensile (min)
- Freezing range
- Thermal conductivity
- Hardness
- Al-Si12
- 10.0–13.0 %
- 2.65 g/cm³
- 190 N/mm²
- 575–565 °C
- 150 W/m·K
- 50–60 HB
Overview
The Best Castability in the LM Series
LM6 is the definitive casting alloy when castability is the overriding requirement. Its Al-Si12 composition places it at the eutectic point of the Al-Si binary phase diagram — the composition that solidifies at the lowest possible temperature (575–565°C) with the narrowest freezing range. This gives LM6 outstanding fluidity, excellent resistance to hot tearing, and the ability to fill the most intricate and thin-wall sections that would be impossible in other alloys.
LM6 is rated 4 (Excellent) for sand, GDC, and LPDC — the only alloy in the general-purpose group to achieve this across all three gravity casting processes. Its minimal copper content (≤0.10%) also gives it the best corrosion resistance of the Group A alloys, making it suitable for marine and chemical plant applications. The trade-off is poor machinability — the high silicon content causes rapid tool wear — and limited strengthening from heat treatment beyond stress relief.
Eutectic Composition — Unique Castability
LM6 at 10–13% Si is at or near the Al-Si eutectic point (12.6%). Eutectic alloys solidify at a fixed temperature (not a range), giving the finest grain structure, the best surface reproduction, the least shrinkage porosity, and the ability to fill the thinnest sections of any casting alloy. For intricate housings, motor end-caps, and complex thin-wall parts, LM6 is the correct specification.
Chemical Composition
LM6 Chemical Composition — BS 1490:1988
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Silicon | Si | 10.0 | 13.0 | 10–13% Si — primary alloying element at or near the eutectic composition (12.6%). Minimum freezing range, maximum fluidity, minimum shrinkage. Responsible for the exceptional castability that defines this alloy. |
| Copper | Cu | — | 0.10 | Strict limit ≤0.10%. LM6 is specifically a low-Cu alloy. The absence of Cu preserves corrosion resistance and enables the alloy to be used in marine, chemical, and food processing environments. |
| Magnesium | Mg | — | 0.10 | Impurity limit ≤0.10%. LM6 is not heat-treatable. Mg is not present in quantities sufficient for precipitation hardening. |
| Iron | Fe | — | 0.6 | Controlled to ≤0.6%. In eutectic Al-Si alloys, Fe forms β-AlFeSi platelets that can impair ductility. Lower Fe limits than HPDC alloys, reflecting GDC/LPDC application. |
| Manganese | Mn | — | 0.5 | Impurity limit. Controlled to maintain clean melt. |
| Nickel | Ni | — | 0.1 | Impurity limit. |
| Zinc | Zn | — | 0.1 | Impurity limit. Higher Zn increases hot-cracking risk. |
| Lead | Pb | — | 0.1 | Impurity limit. |
| Tin | Sn | — | 0.05 | Impurity limit. |
| Titanium | Ti | — | 0.2 | Grain refiner when added as TiB₂ master alloy. |
| Aluminium | Al | — | Remainder | Base metal. Composition verified by OES (ARUN Technology UK, MERLIN-4 ULTRA). |
| Other elements | — | — | 0.05 each / 0.15 total |
Each unspecified element ≤0.05%, total ≤0.15%. |
Global Standards
LM6 Equivalent Grades — International Standards
BS 1490
LM6
Group A · General Purpose Al-Si12
EN 1706
EN AC-44100
EN AC-Al Si12(b)
ASTM / AA
413.0 / A413.0
413.0 — primary US equivalent for LM6
JIS H 5302
ADC2
Al-Si12Fe — eutectic die casting alloy
DIN 1725-2
G-AlSi12
Superseded by EN 1706
ISO 3522
Al-Si12
ISO casting alloy designation
Mechanical Properties
LM6 Mechanical Properties — BS 1490:1988 Table 4
Minimum values from separately cast test samples per BS 1490:1988. These are guaranteed minimums — not average values. Properties in actual castings vary with section thickness, cooling rate, and local geometry.
| Condition | Process | Tensile N/mm² min | 0.2% Proof N/mm² | Elongation % min | Brinell HB |
|---|---|---|---|---|---|
| M | Sand / Investment | 160 | — | 5 | 50–55 |
| M | Chill / GDC | 190 | — | 7 | 55–65 |
| TS | Any | ~160 | — | ~4 | 50–55 |
Physical Properties
LM6 Physical & Thermal Properties
Density
2.65 g/cm³
Approx. 1/3 the density of steel
Freezing Range
575–565 °C
Solidification temperature range
Thermal Conductivity
150 W/m·K
Heat dissipation capability
Electrical Conductivity
37 % IACS
Relative to copper standard
Linear Expansion
20 ×10⁻⁶/K
20–300°C range
Brinell Hardness
50–60 HB
As-cast or stated condition
| Property | Rating | Notes |
|---|---|---|
| Corrosion resistance | Good (B) | Best corrosion resistance of Group A alloys. Low Cu (≤0.10%) preserves resistance. Suitable for marine atmospheres and mild chemical environments. |
| Decorative anodising | Fair (E) | Si content creates a grey-black anodised appearance. Protective anodising effective. Not suitable for decorative bright anodising. |
| Weldability | Excellent | Best weldability of any LM alloy. Widely used in welded assemblies. 10% Si filler rod recommended. |
| Machinability group | 1 — Difficult | Group 1 — hardest to machine in the LM series. High Si causes extreme tool wear. Carbide-tipped or diamond tools required. Allow for higher tooling cost in total part cost calculation. |
Casting Suitability
LM6 Casting Process Suitability — BS 1490:1988 Table 8
Ratings from BS 1490:1988 Table 8. Scale: 4 = Excellent, 3 = Good, 2 = Fair, 1 = Poor, n = Not normally recommended.
Sand Casting
4
Gravity Die Casting (GDC)
4
Low Pressure (LPDC)
4
High Pressure (HPDC)
3
| Castability Property | Rating | Explanation |
|---|---|---|
| Fluidity | 4 — Excellent | Best fluidity of any LM alloy. Eutectic composition gives minimum viscosity and maximum thin-wall fill capability. |
| Resistance to hot tearing | 4 — Excellent | Best hot-tear resistance of any LM alloy. Eutectic solidification eliminates the mushy zone where hot tears form. |
| Pressure tightness | 4 — Excellent | Excellent pressure tightness. Minimal porosity from eutectic solidification. Ideal for hydraulic and pressure-tight castings. |
| Machinability (as-cast) | 1 — Difficult | Group 1 — hardest to machine in the LM series. High Si causes extreme tool wear. Carbide-tipped or diamond tools required. Allow for higher tooling cost in total part cost calculation. |
Heat Treatment
LM6 Heat Treatment — BS 1490:1988 Conditions
M
As Cast
No heat treatment. Used as-cast. Dimensional stability is the priority.
TS
Stress Relieved
200–250°C, 2–4 hours. Reduces residual casting stresses without significant property change.
TB
Solution + Natural Age
Solution treat, quench, age at room temperature. Strength develops over days to weeks.
TB7
Solution + Stabilise
Solution treat, quench, then stabilise at low temperature. Good ductility and dimensional stability.
TE
Artificially Aged Only
Age at 160–180°C, 6–12 hours. Moderate strength improvement without solution treatment.
TF
T6 — Peak Strength
Solution treat + quench + artificial age. Peak strength condition. Full in-house at Creative Alucast.
TF7
T7 — Over-aged / Stabilised
Solution treat + quench + over-age. Slightly lower strength than TF but superior dimensional stability.
Stress Relief Only — Not T6 Heat-Treatable
LM6 cannot be T6 heat-treated. The alloy contains no Mg or Cu in quantities sufficient for precipitation hardening. Only TS (stress relief at 200–250°C) is applicable, primarily to reduce residual casting stresses before precision machining. If strength above 190 N/mm² is required, specify LM25 (GDC) or LM9 (LPDC) instead — both offer T6 capability with comparable castability.
Applications
Typical Applications of LM2
| Industry | Typical Parts | Why LM6 |
|---|---|---|
| Automotive | Thin-wall engine covers, complex inlet manifolds, intricate housings, motor end-caps | Eutectic castability fills complexity that other alloys cannot |
| Marine | Pump bodies, valve housings, marine fittings, seawater components | Best corrosion resistance of Group A alloys |
| Electrical | Motor housings, generator end-caps, electrical enclosures | Complex thin-wall geometry, good electrical conductivity |
| Chemical | Chemical plant housings, filter bodies, pump casings | Corrosion resistance in mild chemical environments |
Thin-Wall Housings
Engine Covers
Inlet Manifolds
Marine Fittings
Motor End-Caps
Pump Bodies
Generator Housings
Electrical Enclosures
Chemical Plant Fittings
Complex Castings
When NOT to Specify LM6
Do not specify LM6 when: (1) machining is a significant part of the manufacturing cost — high Si causes rapid tool wear; use LM25 or LM4 instead; (2) T6 heat treatment is required — not applicable; (3) maximum strength is required — 190 N/mm² is the ceiling; (4) decorative bright anodising is required — LM5 or LM31 perform better.
Frequently Asked Questions
Common Questions About LM6
What is the chemical composition of LM6 aluminium alloy?
LM6 per BS 1490:1988 has nominal composition Al-Si12. Silicon: 10.0–13.0%, Copper: —–0.10%, Magnesium: —–0.10%. The remainder is aluminium with controlled impurity limits.
What is the EN 1706 / European equivalent of LM6?
The EN 1706 equivalent of BS 1490 LM6 is EN AC-44100, with chemical symbol designation EN AC-Al Si12(b). This European standard supersedes the German DIN designation G-AlSi12.
What is the ASTM / AA equivalent of LM6?
The ASTM/Aluminium Association equivalent of LM6 is 413.0 / A413.0. 413.0 — primary US equivalent for LM6.
What is the JIS equivalent of LM6?
The JIS H 5302 equivalent of LM6 is ADC2. Al-Si12Fe — eutectic die casting alloy.
What is the tensile strength of LM6?
The minimum tensile strength of LM6 is 190 N/mm² in the best condition and process per BS 1490:1988 Table 4 (separately cast test samples). Properties vary with casting process and heat treatment condition.
Can LM6 be heat treated to T6?
No — LM6 is not normally heat-treated to T6. Available conditions: M, TS.
What casting processes are suitable for LM6?
Per BS 1490:1988 Table 8: Sand casting (4), Gravity Die Casting (4), Low Pressure Die Casting (4), High Pressure Die Casting (3). Scale: 4=Excellent, 3=Good, 2=Fair, n=Not recommended.
What is the density of LM6 aluminium alloy?
The density of LM6 is 2.65 g/cm³ — approximately one-third the density of steel (7.85 g/cm³), making it ideal for lightweight structural applications.