BS 1490 · Group A · General Purpose
LM25 Aluminium Alloy
Al-Si7Mg0.5 — The most versatile alloy in the BS 1490 series — our go-to recommendation for structural sand-cast parts
Nominal composition
Al-Si7Mg0.5
Silicon content
6.5–7.5%
Density
2.68 g/cm³
T6 tensile (min)
280 N/mm²
Freezing range
615–550°C
Thermal conductivity
150 W/m·K
Hardness
90–100 HB (T6)
Overview
The most versatile alloy in the BS 1490 series — our go-to recommendation for structural sand-cast parts
LM25 — EN AC-42100 in the European system, and equivalent to A356.0/356.0 under ASTM/AA — is the alloy that manages to be good at nearly everything: it casts well, machines cleanly, resists corrosion, and, unlike LM6, responds fully to T6 heat treatment.
That balance comes from its chemistry: 6.5–7.5% silicon for fluidity with low shrinkage, plus controlled magnesium (0.2–0.6%) that enables age-hardening through the Mg₂Si mechanism. Cast and gravity/chill processed, then taken to a T6 condition, LM25 climbs from a 160 N/mm² as-cast baseline to a 280 N/mm² minimum tensile strength — a jump that makes it the standard choice for structural components across automotive, hydraulic and electrical applications.
Best Suited Process
Sand Casting, Gravity Die Casting & Low Pressure Die Casting (all rated 4 — Excellent)
LM25 is rated Excellent for sand casting under BS 1490 Table 8 and is fully heat-treatable to T6 — for structural parts that need real strength on top of good castability, it's usually our first recommendation.
Chemical Composition
LM25 Chemical Composition — BS 1490:1988
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Silicon | Si | 6.5 | 7.5 | Gives good fluidity without the machinability penalty that comes with higher-silicon alloys; low enough to preserve ductility. |
| Magnesium | Mg | 0.20 | 0.60 | Forms Mg₂Si precipitates during T6 ageing. Held near 0.45–0.60% when T6 is planned; kept lower (0.20–0.30%) for as-cast parts to reduce residual stress. |
| Copper | Cu | — | 0.20 | Kept low, unlike LM4 or LM2 — this is what preserves LM25's corrosion resistance and clean T6 response. |
| Iron | Fe | — | 0.50 | Held tighter than most general-purpose alloys, since iron reduces ductility and fatigue life. |
| Manganese | Mn | — | 0.30 | Impurity limit, controlled for melt cleanliness. |
| Zinc | Zn | — | 0.10 | Impurity limit — higher Zn raises hot-cracking risk. |
| Lead | Pb | — | 0.10 | Impurity limit. |
| Tin | Sn | — | 0.05 | Impurity limit. |
| Titanium | Ti | — | 0.20 | Added as a grain refiner (typically TiB₂ master alloy). |
| Aluminium | Al | Remainder | — | Base metal. |
| Other elements | — | — | 0.05 each / 0.15 total | Each unlisted element capped individually and in total. |
Global Standards
LM25 Equivalent Grades — International Standards
BS 1490
LM25
Al-Si5Cu3Mn0.4
EN 1706
EN AC-42100
EN AC-Al Si7Mg0.3, supersedes DIN 1725-2
ASTM / AA
A356.0 / 356.0
A356.0 has a tighter Fe limit (0.20% max) — specify A356.0 for a true LM25 equivalence
JIS H 5302
— (no direct match)
ADC3 (A360) is the nearest Al-Si-Mg die casting alloy
DIN 1725-2
G-AlSi7Mg
Material no. 3.2371, now superseded by EN 1706
ISO 3522
Al-Si7Mg
International standard casting alloy designation
Mechanical Properties
LM25 Mechanical Properties — BS 1490:1988 Table 4
Minimum values from separately cast test samples. These are guaranteed minimums, not averages — properties in an actual casting 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 | 130 | ~65 | 2 | 55–65 |
| M | Chill / GDC | 160 | ~80 | 3 | 60–70 |
| TE | Sand / Investment | 150 | ~90 | 1 | 70–80 |
| TE | Chill / GDC | 190 | ~110 | 2 | 75–85 |
| TB7 | Sand / Investment | 160 | ~100 | 2.5 | 65–75 |
| TB7 | Chill / GDC | 230 | ~170 | 5 | 70–80 |
| TF (T6) | Sand / Investment | 230 | ~190 | — | 85–95 |
| TF (T6) | Chill / GDC / LPDC | 280 | ~220 | 2 | 90–100 |
| TF7 | Chill / GDC | ~230 | ~180 | 3–4 | 75–85 |
Physical Properties
LM25 Physical & Thermal Properties
Density
2.68 g/cm³
About a third the density of steel
Freezing range
615–550°C
A wide, 65°C range gives good feedability
Thermal conductivity
150 W/m·K
Excellent heat dissipation
Electrical conductivity
39% IACS
Good for electrical housings
Linear expansion
21 ×10⁻⁶/K
20–300°C range
Elastic modulus
~71 GPa
About a third that of steel
Working Properties
Corrosion, Finishing & Machining
Corrosion resistance
GoodLow copper (≤0.20%) suits most atmospheric and mild chemical environments.
Decorative anodising
FairSilicon gives a grey anodised finish; protective anodising works well, bright decorative anodising doesn't.
Weldability
GoodWelds readily with a 5% Si filler rod (BS 2L99); low copper avoids hot cracking, and a post-weld T6 restores full strength.
Machinability
GoodT6 hardening actually improves chip formation, so machining gets easier once heat treated.
Casting Suitability
LM25 Casting Process Suitability — BS 1490:1988 Table 8
Scale: 4 = Excellent, 3 = Good, 2 = Fair, 1 = Poor, n = possible but not normally recommended.
4
Sand Casting
4
Gravity Die Casting
4
Low Pressure Die Casting
3n
High Pressure Die Casting
Heat Treatment
LM25 Heat Treatment — BS 1490:1988 Conditions
LM25 is the most heat-treatable alloy in the BS 1490 LM series — every standard condition applies, from as-cast (M) through to full T6 (TF). We can produce the same casting design in different conditions without retooling, matching the treatment to what the application needs. Full T6 involves solution treatment around 515–525°C, a fast water quench, and artificial ageing at 155–175°C.
Applications
Typical Applications of LM25
Automotive
Cylinder heads, inlet manifolds, suspension brackets, gearbox housings, oil pump bodies, wheel hubs
Why LM25: T6 strength plus pressure tightness and weight saving over iron castings
Power & Energy
Pump casings, impellers, valve bodies, hydraulic manifolds, compressor housings
Why LM25: Rated Excellent for pressure tightness, with good corrosion resistance and machinability
Electrical
Motor housings, alternator casings, electrical enclosures, heat sinks
Why LM25: 150 W/m·K thermal conductivity and 39% IACS electrical conductivity
Pump & Valves
Pump bodies, impeller casings, valve housings, manifold blocks, filter housings
Why LM25: Excellent pressure tightness and corrosion resistance on sealing surfaces
Fire Safety
Pump casings, valve bodies, nozzle housings, coupling flanges
Why LM25: Pressure tightness and corrosion resistance in wet-service environments
When Not To Specify LM25
- —Bright decorative anodising is required — LM5 or LM31 give a better finish.
- —Sustained service is above roughly 250°C — LM13 or LM26 hold up better at temperature.
- —You need the highest as-cast tensile strength without any heat treatment step — LM31 is worth considering.
- —You're producing very high volumes by HPDC — LM2 or LM24 are the die-casting specialists.
Frequently Asked Questions
Common Questions About LM25
What is the chemical composition of LM25?
Per BS 1490:1988, LM25 has a nominal composition of Al-Si7Mg0.5 — Silicon 6.5–7.5%, Copper up to 0.20%, Magnesium 0.20–0.60%, with the balance aluminium and controlled impurity limits on Fe, Mn, Ni, Zn, Pb, Sn and Ti.
What is the European (EN 1706) equivalent of LM25?
EN AC-42100 (EN AC-Al Si7Mg0.3), which supersedes the older German DIN designation G-AlSi7Mg (material no. 3.2371).
What is the ASTM equivalent of LM25?
A356.0 (preferred) or 356.0. A356.0 has a tighter iron limit (0.20% max versus 0.50% for 356.0), making it the more accurate US equivalent — worth specifying explicitly on drawings.
Can LM25 be heat treated to T6?
Yes — LM25 fully responds to T6: solution treat around 515–525°C, water quench, then artificially age at 155–175°C. This takes tensile strength to a 280 N/mm² minimum in gravity/chill-cast condition.
Which casting processes suit LM25?
Per BS 1490 Table 8: Sand casting, Gravity Die Casting and Low Pressure Die Casting are all rated 4 (Excellent); High Pressure Die Casting is rated 3n (possible, not the preferred route).
What is the density of LM25?
2.68 g/cm³ — roughly a third the density of steel.
Where can I get LM25 aluminium castings made in India?
Metline Casting, based in Rajkot, Gujarat, produces LM25 components by sand casting, cast and finished in-house from core making through to machining. Get in touch with your drawing or sample to discuss your requirement.
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From core making to finished, inspected components, Metline Casting runs the full aluminium casting process in-house.