BS 1490 · Group A · General Purpose
lm25
Aluminium Alloy
Al-Si7Mg0.5 — The Most Versatile Aluminium Casting Alloy in the BS 1490 Series
Sand Casting
Gravity Die Casting
Low Pressure Die Casting
T6 Heat-Treatable
ISO 9001:2015
At a Glance
- Nominal composition
- Si content
- Density
- T6 tensile (GDC min)
- Freezing range
- Thermal conductivity
- Hardness
- Al-Si7Mg0.5
- 6.5–7.5 %
- 2.68 g/cm³
- 280 N/mm²
- 615–550 °C
- 150 W/m·K
- 90–100 HB (T6)
Overview
The Most Versatile Aluminium Casting Alloy in the BS 1490 Series
LM25 — designated EN AC-42100 in the European system and equivalent to A356.0/356.0 in the ASTM/AA classification — occupies a unique position in aluminium casting metallurgy. No other alloy in the BS 1490 LM-series achieves its combination across all four dimensions that matter: castability, mechanical performance, corrosion resistance, and heat-treatability.
The alloy’s Al-Si7Mg chemistry positions it in the hypoeutectic region of the Al-Si phase diagram — 6.5–7.5% silicon for excellent fluidity and low shrinkage, combined with controlled magnesium (0.2–0.6%) that enables precipitation hardening through the Mg₂Si mechanism during T6 heat treatment. The result: a chill-cast T6 alloy delivering a minimum tensile strength of 280 N/mm² against an as-cast baseline of 160 N/mm². At Creative Alucast, LM25 is produced with a fully modified eutectic structure, verified in-house by metallurgical microscope (MATRIX 3000M).
Modified Microstructure — Standard Practice at Creative Alucast
All LM25 castings at Creative Alucast are produced with a fully modified eutectic structure. Modification refines the silicon morphology from coarse acicular platelets to fine fibrous particles, improving elongation by up to 40% and fatigue strength by 15–20% versus unmodified material.
Chemical Composition
LM25 Chemical Composition — BS 1490:1988
| Element | Symbol | Min % | Max % | Role in alloy |
|---|---|---|---|---|
| Silicon | Si | 6.5 | 7.5 | 6.5–7.5% Si — primary alloying element. Provides good fluidity without the machinability penalty of higher-Si alloys. Hypoeutectic composition preserves ductility. |
| Magnesium | Mg | 0.20 | 0.60 | 0.20–0.60% Mg — forms Mg₂Si precipitates during T6 ageing. For T6 specify Mg 0.45–0.60%. For as-cast (M) condition keep Mg near 0.20–0.30% to reduce residual stress. |
| Copper | Cu | — | 0.20 | Strict limit ≤0.20%. Low Cu preserves excellent corrosion resistance and clean T6 response. LM25 is deliberately Cu-free unlike LM4, LM24, and LM27. |
| Iron | Fe | — | 0.50 | ≤0.50% — tighter than most general-purpose alloys. Fe forms β-AlFeSi platelets reducing ductility and fatigue life. Verified in every heat by ARUN Technology MERLIN-4 ULTRA OES spectrometer. |
| Manganese | Mn | — | 0.30 | Impurity limit. Controlled to maintain clean melt. |
| Zinc | Zn | — | 0.10 | Impurity limit. Higher Zn increases hot-cracking risk. |
| Lead | Pb | — | 0.10 | Impurity limit. |
| Tin | Sn | — | 0.05 | Impurity limit. |
| Titanium | Ti | — | 0.20 | 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%. |
Magnesium Control — Critical for T6
When castings are to be T6 heat-treated, Mg content should be maintained near the upper limit (0.45–0.60%). For as-cast (M) condition parts, keep Mg near the lower limit (0.20–0.30%). This is agreed at order stage and controlled by melt chemistry verification using our in-house OES spectrometer before every pour.
Global Standards
LM25 Equivalent Grades— International Standards
BS 1490
LM25
Group B · Special Purpose 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 = tighter Fe (0.20% max) Specify A356.0 for LM25 equivalence
JIS H 5302
— (no direct)
ADC3 (A360) is 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
A356.0 vs 356.0 — Specify Carefully
A356.0 has a tighter iron limit (0.20% max vs 0.50% for 356.0) — making it the correct US equivalent for LM25. Always specify A356.0 on drawings when ordering to ASTM specification. Similarly, EN AC-42100 is the correct European equivalent, not EN AC-42000.
Mechanical Properties
LM25 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 vary with section thickness, cooling rate, and 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 | Sand / Investment | 230 | ~190 | — | 85–95 |
| TF | Chill / GDC / LPDC | 280 | ~220 | 2 | 90–100 |
| TF7 | Chill / GDC | ~230 | ~180 | 3–4 | 75–85 |
Tensile — M condition (GDC)
160 N/mm²
As-cast minimum
Tensile — TF / T6 (GDC)
280 N/mm²
+75% over as-cast
Proof Stress — M
~80 N/mm²
As-cast typical
Proof Stress — TF / T6
~220 N/mm²
+175% over as-cast
Physical Properties
LM25 Physical & Thermal Properties
Density
2.68 g/cm³
Approx. 1/3 the density of steel
Freezing Range
615–550 °C
65°C range — 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
Approx. 1/3 that of steel
| Property | Rating | Notes |
|---|---|---|
| Corrosion resistance | Good (B) | Low Cu (≤0.20%) gives good corrosion resistance. Suitable for most atmospheric and mild chemical environments. |
| Decorative anodising | Fair (D) | Si content produces grey anodised appearance. Protective Type II and III anodising fully applicable. Not suitable for bright decorative anodising. |
| Weldability | Good | Readily welded using 5% Si filler rod (BS 2L99). Low Cu prevents hot cracking. Post-weld T6 restores full strength. |
| Machinability group | 3 — Good | Group 3 per BS 1490 Table 7. T6 significantly improves chip formation — harder Si particles cut cleanly. |
| Fatigue endurance limit | 70–110 MPa | For 5×10⁷ cycles. T6 condition and modified microstructure improve fatigue performance significantly. |
Casting Suitability
LM25 Casting Process Suitability — BS 1490:1988 Table 8
Ratings from BS 1490:1988 Table 8. Scale: 4 = Excellent, 3 = Good, 2 = Fair, n = Not normally recommended.
Sand Casting
4
Gravity Die Casting (GDC)
4
Low Pressure Die Casting (LPDC)
4
High Pressure Die Casting (HPDC)
3n
| Castability Property | Rating | Explanation |
|---|---|---|
| Fluidity | 3 — Good | 7% Si gives good mould filling. Tilt GDC process provides controlled fill minimising turbulence and oxide inclusions. |
| Resistance to hot tearing | 4 — Excellent | Very low susceptibility to hot cracking. Hypoeutectic composition avoids the problematic intermediate Si range. |
| Pressure tightness | 4 — Excellent | Outstanding for hydraulic and pneumatic components. Verified with in-house FOSECO RPT unit and density analyser. |
| Machinability (as-cast) | 3 — Good | Group 3 per BS 1490 Table 7. T6 significantly improves chip formation — harder Si particles cut cleanly. |
LM25 vs LM6 — The Most Common Selection Decision
Both alloys rate 4 (Excellent) for Sand, GDC, and LPDC. Choose LM6 when castability is the only requirement and no heat treatment is planned. Choose LM25 when tensile strength above 160 N/mm² is required, when T6 is specified, or when machined dimensions must hold consistent hardness batch-to-batch.
Heat Treatment
LM25 Heat Treatment — All BS 1490 Conditions Applicable
LM25 is the most heat-treatable alloy in the BS 1490 LM-series — all six conditions apply. The same casting design can be supplied in M, TE, TB7, TF, or TF7 condition without retooling.
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.
In-House T6 — Full Batch Traceability at Creative Alucast
Full T6 (TF condition) is performed in-house using our horizontal solution treatment furnace. (1) Solution treat 515–525°C, 6–12 hours. (2) Water quench 60–80°C, transfer under 30 seconds. (3) Artificial age 155–175°C, 6–12 hours. Brinell hardness verified on every batch by FIE digital Brinell tester before despatch. Certificate of conformance available on request.
Applications
Typical Applications of LM25
| Industry | Typical Parts | Why LM13 |
|---|---|---|
| Automotive | Cylinder heads, inlet manifolds, suspension brackets, gearbox housings, oil pump bodies, wheel hubs | T6 strength + pressure tightness + weight saving vs. iron castings |
| Power & Energy | Pump casings, impellers, valve bodies, hydraulic manifolds, compressor housings | Pressure tightness rated 4, corrosion resistance, machinability |
| Electrical | Motor housings, alternator casings, electrical enclosures, heat sinks | Thermal conductivity 150 W/m·K, electrical conductivity 39% IACS, EMI shielding |
| Pump & Valves | Pump bodies, impeller casings, valve housings, manifold blocks, filter housings | Excellent pressure tightness, corrosion resistance, hydraulic sealing surfaces |
| Medical Devices | Equipment frames, instrument housings, diagnostic device components | Light weight, corrosion resistance, sterilisable, machinable to tight tolerances |
| Fire Industry | Pump casings, valve bodies, nozzle housings, coupling flanges | Pressure tightness, wet-environment corrosion resistance, strength-to-weight |
When NOT to Specify LM25
Do not specify LM25 when: (1) bright decorative anodising is required — specify LM5 or LM31; (2) sustained service above 250°C — specify LM13 or LM26; (3) highest as-cast tensile without heat treatment is the priority — consider LM31; (4) high-volume HPDC above 50,000 pcs/year — specify LM2 or LM24.
Cylinder Heads
Wheel Hubs
Pump Bodies
Gearbox Housings
Motor Housings
Valve Bodies
Heat Sinks
Oil Pump Bodies
Inlet Manifolds
Filter Housings
Impeller Casings
Medical Frames
Fire Pump Casings
LPDC Structural Parts
Suspension Brackets
Hydraulic Manifolds
Compressor Housings
Frequently Asked Questions
Common Questions About LM25
What is the chemical composition of LM25 aluminium alloy?
LM25 per BS 1490:1988 has nominal composition Al-Si7Mg0.5. Silicon: 6.5–7.5%, Copper: ≤0.20%, Magnesium: 0.20–0.60%. Aluminium forms the remainder with controlled impurity limits on Fe, Mn, Ni, Zn, Pb, Sn, Ti.
What is the EN 1706 / European equivalent of LM25?
The EN 1706 equivalent of BS 1490 LM25 is EN AC-42100, with chemical symbol designation EN AC-Al Si7Mg0.3. This European standard supersedes the German DIN designation G-AlSi7Mg (material no. 3.2371).
What is the ASTM equivalent of LM25?
The ASTM/AA equivalent of LM25 is A356.0 (preferred) or 356.0. A356.0 has a tighter iron limit (0.20% max vs 0.50% for 356.0) making it the correct US equivalent for LM25. Always specify A356.0 on drawings.
What is the tensile strength of LM25?
LM25 tensile strength per BS 1490:1988 Table 4: As-cast (M) GDC minimum 160 N/mm². T6 (TF) GDC minimum 280 N/mm². T6 sand minimum 230 N/mm². Values are minimums from separately cast test samples.
Can LM25 be heat treated to T6?
Yes. LM25 fully responds to T6 heat treatment (TF condition): solution treat at 515–525°C, water quench, artificially age at 155–175°C. Delivers 280 N/mm² minimum tensile in GDC/LPDC. Full in-house T6 at Creative Alucast with batch Brinell hardness verification.
What casting processes are suitable for LM25?
Per BS 1490:1988 Table 8: Sand casting 4 (Excellent), Gravity Die Casting 4 (Excellent), Low Pressure Die Casting 4 (Excellent), High Pressure Die Casting 3n (possible but not normally recommended). LM25 is the only Group A alloy rated Excellent for all three gravity processes.
What is the density of LM25?
The density of LM25 is 2.68 g/cm³ — approximately one-third the density of steel (7.85 g/cm³).
What is the JIS equivalent of LM25?
There is no direct JIS H 5302 equivalent for BS 1490 LM25. ADC3 (A360.0, Al-Si-Mg series) is the nearest JIS die casting alloy. For wrought equivalents, AC4C is comparable.
Where can I source LM25 aluminium castings in India?
Creative Alucast LLP in Rajkot, Gujarat produces LM25 castings by sand casting, gravity die casting (GDC), and low pressure die casting (LPDC). Full in-house T6 heat treatment. ISO 9001:2015. Contact: info@creativealucast.com or +91-98989 34099.