BS 1490 · Group A · General Purpose
lm27
Aluminium Alloy
Al-Si10Cu2 — The Primary High-Pressure Die Casting Alloy
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-Si7Cu2Mn0.5
- 6.0–8.0 %
- 2.75 g/cm³
- 160 N/mm²
- 605–525 °C
- 138 W/m·K
- 70–90 HB
Overview
General Engineering — Similar to LM4 with Higher Silicon
LM27 is a general-purpose Al-Si-Cu-Mn alloy positioned between LM4 (Si5Cu3) and LM25 (Si7Mg) in the BS 1490 Group A alloys. Its 6–8% Si provides better castability than LM4 while its 1.5–2.5% Cu addition gives improved as-cast strength and machinability over the Cu-free LM25. LM27 is rated 4 (Excellent) for both sand and gravity die casting.
LM27 is used primarily in the as-cast (M) condition for general engineering applications. BS 1490 lists it as only available in M condition — unlike LM4 which has a TF option. The alloy’s mechanical properties are modest by current standards, and for most new designs where LM27 might be considered, LM25 is the preferred specification offering better corrosion resistance and full T6 capability.
Similar to LM4 — Moderate Si Version
LM27 occupies the same general-purpose space as LM4 but with higher Si (6–8% vs 4–6%) giving better castability, and slightly lower Cu (1.5–2.5% vs 2–4%) giving slightly better corrosion resistance. Rated 4 (Excellent) for sand and GDC — one of only a few alloys to achieve this. Available where LM4 is not — some foundries stock LM27 as a standard melt.
Chemical Composition
LM27 Chemical Composition — BS 1490:1988
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Silicon | Si | 6.0 | 8.0 | 6–8% Si — higher than LM4 (4–6%) giving improved castability. Below the eutectic level of LM6/LM9 — some ductility preserved. |
| Copper | Cu | 1.5 | 2.5 | 1.5–2.5% Cu — lower than LM4. Improves as-cast strength and machinability without the corrosion penalty of higher Cu alloys. |
| Magnesium | Mg | — | 0.35 | Impurity limit ≤0.35%. LM27 is only available in as-cast condition — Mg is not specified for heat treatment purposes. |
| Iron | Fe | — | 0.8 | Up to 0.8% Fe. Moderate Fe limit consistent with GDC application. |
| Manganese | Mn | 0.2 | 0.6 | Impurity limit. Controlled to maintain clean melt. |
| Nickel | Ni | — | 0.3 | Impurity limit. |
| Zinc | Zn | — | 1.0 | Impurity limit. Higher Zn increases hot-cracking risk. |
| Lead | Pb | — | 0.2 | Impurity limit. |
| Tin | Sn | — | 0.1 | 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
LM27 Equivalent Grades — International Standards
BS 1490
LM27
Group A · General Purpose Al-Si7Cu2Mn0.5
EN 1706
EN AC-46300
EN AC-Al Si7Cu3Mg
ASTM / AA
380.0
380.0 — approximate US equivalent
JIS H 5302
—
No direct JIS equivalent
DIN 1725-2
G-AlSi7Cu3
Superseded by EN 1706
ISO 3522
Al-Si7Cu3
ISO casting alloy designation
Mechanical Properties
LM27 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 | 140 | — | 1 | 70–80 |
| M | Chill / GDC | 160 | — | 2 | 80–90 |
Physical Properties
LM27 Physical & Thermal Properties
Density
2.75 g/cm³
Approx. 1/3 the density of steel
Freezing Range
605–525 °C
Solidification temperature range
Thermal Conductivity
138 W/m·K
Heat dissipation capability
Electrical Conductivity
27 % IACS
Relative to copper standard
Linear Expansion
21 ×10⁻⁶/K
20–300°C range
Brinell Hardness
70–90 HB
As-cast or stated condition
| Property | Rating | Notes |
|---|---|---|
| Corrosion resistance | Good (B) | Better than LM2/LM4/LM24 due to lower Cu. Suitable for general atmospheric use. |
| Decorative anodising | Poor (D) | Cu content limits anodising quality. |
| Weldability | Fair | Weldable with care. Use 5% Si filler rod. |
| Machinability group | 3 Good | Group 3 machinability. Cu content improves chip formation. |
Casting Suitability
LM27 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)
3
High Pressure (HPDC)
3n
| Castability Property | Rating | Explanation |
|---|---|---|
| Fluidity | 3 — Good | Good fluidity from 6–8% Si. Better than LM4, approaching LM25 level. |
| Resistance to hot tearing | 4 — Excellent | Good resistance to hot tearing. |
| Pressure tightness | 4 — Excellent | Good pressure tightness. |
| Machinability (as-cast) | 3 — Good | Group 3 machinability. Cu content improves chip formation. |
Heat Treatment
LM27 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.
As-Cast Only per BS 1490
LM27 is specified only in the M (as-cast) condition in BS 1490:1988. Although the Cu content would allow a limited T6 response if Mg were controlled, the alloy is not formally heat-treated. For T6-capable alloys with comparable Si levels, specify LM25 (Cu-free, T6 excellent) or LM16 (Si5Cu1Mg, TF capable).
Applications
Typical Applications of LM27
| Industry | Typical Parts | Why LM13 |
|---|---|---|
| General Engineering | General structural castings, housings, covers, brackets | Good castability + moderate strength in as-cast state |
| Automotive | General automotive castings not requiring T6 | Widely available, proven foundry alloy |
| Industrial | Machine components, equipment housings | Readily available and consistent in GDC |
Structural Castings
General Housings
Covers
Automotive Brackets
Machine Components
Equipment Housings
When NOT to Specify LM27
For most new designs, LM25 should be preferred over LM27 — it offers better corrosion resistance, full T6 capability, and wider global availability. Specify LM27 when established supplier melt practice is already on LM27, or when a specific existing qualification is in LM27.
Frequently Asked Questions
Common Questions About LM27
What is the chemical composition of LM27 aluminium alloy?
LM27 per BS 1490:1988 has nominal composition Al-Si7Cu2Mn0.5. Silicon: 6.0–8.0%, Copper: 1.5–2.5%, Magnesium: —–0.35%. The remainder is aluminium with controlled impurity limits.
What is the EN 1706 / European equivalent of LM27?
The EN 1706 equivalent of BS 1490 LM27 is EN AC-46300, with chemical symbol designation EN AC-Al Si7Cu3Mg. This European standard supersedes the German DIN designation G-AlSi7Cu3.
What is the ASTM / AA equivalent of LM27?
The ASTM/Aluminium Association equivalent of LM27 is 380.0. 380.0 — approximate US equivalent.
What is the JIS equivalent of LM27?
There is no direct JIS H 5302 equivalent for LM27. No direct JIS equivalent.
What is the tensile strength of LM27?
The minimum tensile strength of LM27 is 160 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 LM27 be heat treated to T6?
No — LM27 is not normally heat-treated to T6. Available conditions: M.
What casting processes are suitable for LM27?
Per BS 1490:1988 Table 8: Sand casting (4), Gravity Die Casting (4), Low Pressure Die Casting (3), High Pressure Die Casting (3n). Scale: 4=Excellent, 3=Good, 2=Fair, n=Not recommended.
What is the density of LM27 aluminium alloy?
The density of LM27 is 2.75 g/cm³ — approximately one-third the density of steel (7.85 g/cm³), making it ideal for lightweight structural applications.