BS 1490 · Group A · General Purpose
lm4
Aluminium Alloy
Al-Si5Cu3Mn0.5 — The Most Versatile General-Purpose Casting Alloy
Sand Casting
Gravity Die Casting
Low Pressure Die Casting
High Pressure Die Casting
T6 Heat-Treatable
ISO 9001:2015
At a Glance
- Nominal composition
- Si content
- Density
- Best tensile (min)
- Freezing range
- Thermal conductivity
- Hardness
- Al-Si5Cu3Mn0.5
- 4.0–6.0 %
- 2.73 g/cm³
- 280 N/mm²
- 620–520 °C
- 121 W/m·K
- 70–85 HB
Overview
The Most Versatile General-Purpose Casting Alloy
LM4 is the most widely applicable general-purpose aluminium casting alloy in the BS 1490 series, rated 4 (Excellent) for sand casting, gravity die casting, and investment casting. Its Al-Si5Cu3Mn composition delivers a reliable combination of castability, moderate strength, and good machinability suitable for an almost unlimited range of engineering applications.
The alloy’s 4–6% silicon provides sufficient fluidity for both thin and thick section castings, while 2–4% copper gives as-cast strength and excellent machinability. The addition of 0.2–0.6% manganese improves high-temperature strength. LM4 responds to T6 heat treatment, delivering tensile strengths up to 280 N/mm² in GDC — though LM25 is typically preferred when T6 strength is the primary requirement.
Foundry First Choice
LM4 is the alloy specified first when no overriding requirement points to a specialist alloy. Good foundry characteristics permit its use by all casting processes for thin or thick sections. Available from a wide range of manufacturers globally. Where LM25 is not specified, LM4 is almost always the correct general-purpose choice.
Chemical Composition
LM4 Chemical Composition — BS 1490:1988
| Element | Symbol | Min % | Max % | Role in alloy |
|---|---|---|---|---|
| Silicon | Si | 4.0 | 6.0 | 4–6% Si provides good fluidity for all casting processes. Lower Si than LM6/LM9 — alloy is not eutectic, giving a wider freezing range and good feeding characteristics in thick sections. |
| Copper | Cu | 2.0 | 4.0 | 2–4% Cu is the primary strengthening element. It improves as-cast strength and machinability significantly. It reduces corrosion resistance and is not suitable for marine or food use. |
| Magnesium | Mg | — | 0.20 | Impurity limit only (≤0.20%). For T6 heat treatment to be effective, Mg must be near the upper limit. If T6 is required, specify Mg 0.15–0.20% minimum. |
| Iron | Fe | — | 0.8 | Controlled to ≤0.8%. Higher Fe reduces ductility. This is lower than HPDC alloys because LM4 is intended for sand and GDC applications where some ductility is needed. |
| Manganese | Mn | 0.2 | 0.6 | Impurity limit. Controlled to maintain a clean melt. |
| Nickel | Ni | — | 0.3 | Impurity limit. |
| Zinc | Zn | — | 0.5 | Impurity limit. Higher Zn increases hot-cracking risk. |
| Lead | Pb | — | 0.1 | 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 using ARUN Technology UK, MERLIN-4 ULTRA. | |
| Other elements | — | — | 0.05 each / 0.15 total | Each unspecified element ≤0.05%, with a total limit of ≤0.15%. |
Global Standards
LM4 Equivalent Grades — International Standards
BS 1490
LM4
Group A · General Purpose Al-Si5Cu3Mn0.5
EN 1706
EN AC-45300
EN AC-Al Si5Cu3Mn
ASTM / AA
319.0
319.0 is the primary US equivalent
JIS H 5302
—
No direct JIS equivalent
DIN 1725-2
G-AlSi5Cu3
Superseded by EN 1706
ISO 3522
Al-Si5Cu3
ISO casting alloy designation
Mechanical Properties
LM4 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 | — | 2 | 70–80 |
| M | Chill / GDC | 160 | — | 2 | 80–90 |
| TF | Sand / Investment | 230 | — | — | 95–110 |
| TF | Chill / GDC | 280 | — | — | 100–115 |
Physical Properties
LM4Physical & Therma Properties
Density
2.73 g/cm³
Approx. 1/3 the density of steel
Freezing Range
620–520 °C
Solidification temperature range
Thermal Conductivity
121 W/m·K
Heat dissipation capability
Electrical Conductivity
— % IACS
Relative to copper standard
Linear Expansion
21 ×10⁻⁶/K
20–300°C range
Brinell Brinell Hardness
70–85 HB
As-cast or stated condition
| Property | Rating | Notes |
|---|---|---|
| Corrosion resistance | Fair (D) | Cu content reduces corrosion resistance. Suitable for normal atmospheric conditions. Not recommended for marine or food processing environments. |
| Decorative anodising | Poor (D) | Cu content causes poor anodising quality. Not suitable for decorative anodising. |
| Weldability | Good | Weldable using gas or argon arc with 5% Si filler rod. Heat treatment should follow welding to restore properties. |
| Machinability group | 3 — Good | Group 3 machinability. Cu content significantly improves chip formation compared to pure Al-Si alloys. |
Casting Suitability
LM4 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 | 5% Si gives good but not outstanding fluidity. Adequate for most geometries with correct gating. |
| Resistance to hot tearing | 3 — Good | Good resistance to hot tearing. Wider freezing range than LM6 requires careful feeding design in heavy sections. |
| Pressure tightness | 4 — Excellent | Excellent pressure tightness when correctly cast. Widely used for hydraulic and pressure-tight components. |
| Machinability (as-cast) | 3 — Good | Group 3 machinability. Cu content significantly improves chip formation compared to pure Al-Si alloys. |
Heat Treatment
LM4 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.
T6 Heat Treatment — Applicable but Mg-Dependent
LM4 responds to T6 heat treatment (TF condition) but only when Mg content is near the upper end of the permitted range (0.15–0.20%). If Mg is at the lower limit, the T6 response is poor. When ordering LM4 for T6 applications, specify Mg minimum 0.15% on the order. For reliable T6 performance across the full composition range, LM16 or LM25 are preferred.
Applications
Typical Applications of LM4
| Industry | Typical Parts | Why LM4 |
|---|---|---|
| Automotive | Engine components, gearbox housings, transmission parts, pump bodies | Versatile — works in sand, GDC, and LPDC. T6 available when needed. |
| Electrical | Switchgear housings, motor frames, electrical tools | Good strength and machinability for precision machined bores |
| General Engineering | Domestic appliances, office equipment, household fittings | Widest availability and lowest premium vs. specialist alloys |
| Industrial | Machine parts, agricultural equipment, moderate-load structural parts | Excellent castability in all processes at all section thicknesses |
Engine Components
Gearbox Housings
Pump Bodies
Switchgear
Motor Frames
Electrical Tools
Machine Parts
Agricultural Equipment
Domestic Appliances
Transmission Parts
When NOT to Specify LM4
Do not specify LM4 when: (1) maximum corrosion resistance is required — use LM6 or LM5; (2) decorative anodising is specified — use LM5 or LM31; (3) high-silicon HPDC at maximum volume is required — use LM2 or LM24; (4) the highest possible as-cast strength without heat treatment is needed — consider LM31.
Frequently Asked Questions
Common Questions About LM4
Common questions from engineers designing for aluminium casting for the first time — or redesigning a part that isn’t performing as expected.
What is the chemical composition of LM4 aluminium alloy?
LM4 per BS 1490:1988 has nominal composition Al-Si5Cu3Mn0.5. Silicon: 4.0–6.0%, Copper: 2.0–4.0%, Magnesium: —–0.20%. The remainder is aluminium with controlled impurity limits.
What is the EN 1706 / European equivalent of LM4?
The EN 1706 equivalent of BS 1490 LM4 is EN AC-45300, with chemical symbol designation EN AC-Al Si5Cu3Mn. This European standard supersedes the German DIN designation G-AlSi5Cu3.
What is the ASTM / AA equivalent of LM4?
The ASTM/Aluminium Association equivalent of LM4 is 319.0. 319.0 is the primary US equivalent.
What is the JIS equivalent of LM4?
There is no direct JIS H 5302 equivalent for LM4. No direct JIS equivalent.
What is the tensile strength of LM4?
The minimum tensile strength of LM4 is 280 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 LM4 be heat treated to T6?
Yes — LM4 is T6 heat-treatable (TF condition). Solution treat at 515–525°C, water quench, artificially age at 155–175°C. Full in-house T6 available at Creative Alucast with batch hardness verification.
What casting processes are suitable for LM4?
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 LM4 aluminium alloy?
The density of LM4 is 2.73 g/cm³ — approximately one-third the density of steel (7.85 g/cm³), making it ideal for lightweight structural applications.