BS 1490 · Group B · Special Purpose
LM13
Aluminium Alloy
Al-Si12Cu1Mg1 — The Piston Alloy — Elevated Temperature Performance
Sand Casting
Gravity Die Casting
Low 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-Si12Cu1Mg1
- 10.0–13.0 %
- 2.70 g/cm³
- 280 N/mm²
- 575–520 °C
- 138 W/m·K
- 100–130 (mandatory per BS 1490) HB
Overview
The Piston Alloy — Elevated Temperature Performance
LM13 is the principal aluminium piston alloy in the BS 1490 series, specifically formulated for components operating continuously at elevated temperatures up to 250–300°C. The Al-Si12Cu1Mg1 composition combines the eutectic Si level of LM6 with both copper (0.7–1.5%) and magnesium (0.8–1.5%) for complex heat treatment capability and low thermal expansion.
The alloy’s combination of near-eutectic silicon, nickel (up to 1.5%), copper, and magnesium creates a complex precipitation-hardening system that maintains strength at temperatures where standard Al-Si alloys soften significantly. Hardness requirements per BS 1490 are mandatory for LM13 (unlike most other alloys) because hardness is the practical measure of elevated-temperature service integrity.
Requires Metallographic Control — BS 1490 Clause 5.4
LM13 is subject to mandatory microstructure requirements under BS 1490 — the average size of primary silicon crystallites shall not exceed 40µm and maximum individual particle size shall not exceed 70µm. This requires phosphorus modification of the hypereutectic silicon structure. Microstructure is verified by metallurgical microscope.
Chemical Composition
LM13 Chemical Composition —BS 1490:1988
| Element | Symbol | Min % | Max % | Role in alloy |
|---|---|---|---|---|
| Silicon | Si | 10.0 | 13.0 | 10–13% Si at near-eutectic level. Provides good castability and, in this Cu-Mg-Ni alloying system, forms a complex multi-phase microstructure stable at elevated temperature. |
| Copper | Cu | 0.7 | 1.5 | 0.7–1.5% Cu contributes to elevated-temperature strength through CuAl₂ precipitation. Works in combination with Mg₂Si precipitates from the Mg content. |
| Magnesium | Mg | 0.8 | 1.5 | 0.8–1.5% Mg — higher Mg range than most alloys. Forms Mg₂Si precipitates and contributes to the complex precipitation system that maintains strength to 250°C+. |
| Iron | Fe | — | 1.0 | Up to 1.0% Fe. In this complex alloy system, Fe forms Ni-Fe-Al compounds that contribute to elevated-temperature strength. |
| Manganese | Mn | — | 0.5 | Impurity limit. Controlled to maintain clean melt. |
| Nickel | Ni | — | 1.5 | 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 (ARUN Technology UK, MERLIN-4 ULTRA). | |
| Other elements | — | — | 0.05 each / 0.15 total | Each unspecified element ≤0.05%, total ≤0.15%. |
Global Standards
LM13 Equivalent Grades — International Standards
BS 1490
LM13
Group B · Special Purpose Al-Si12Cu1Mg1
EN 1706
EN AC-48000
EN AC-Al Si12CuNiMg
ASTM / AA
—
No direct ASTM equivalent
JIS H 5302
—
No direct JIS equivalent
DIN 1725-2
G-AlSi12CuMgNi
Superseded by EN 1706
ISO 3522
Al-Si12CuNiMg
ISO casting alloy designation
Mechanical Properties
LM13 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 |
|---|---|---|---|---|---|
| TE | Chill / GDC | 210 | — | — | 90–130 |
| TF | Chill / GDC | 280 | — | — | 100–150 |
| TF7 | Chill / GDC | 200 | — | — | 65–90 |
Physical Properties
LM13 Physical & Thermal Properties
Density
2.70 g/cm³
Approx. 1/3 the density of steel
Freezing Range
575–520 °C
Solidification temperature range
Thermal Conductivity
138 W/m·K
Heat dissipation capability
Electrical Conductivity
— % IACS
Relative to copper standard
Linear Expansion
20 ×10⁻⁶/K
20–300°C range
As-cast or stated condition
100–130 (mandatory per BS 1490) HB
Brinell Hardness
| Property | Rating | Notes |
|---|---|---|
| Corrosion resistance | Fair (C) | Moderate corrosion resistance. Cu content reduces resistance. Typically used in internal engine applications not exposed to external corrosion. |
| Decorative anodising | Poor (D) | Not suitable for decorative anodising. Complex alloy system gives poor anodised appearance. |
| Weldability | Poor | High Cu content and complex microstructure make LM13 poorly weldable. Not recommended for welded assemblies. |
| Machinability group | 2 — Fair | Group 2 machinability. High Si plus Ni compounds require carbide or diamond tooling. |
Casting Suitability
LM13 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
3
Gravity Die Casting (GDC)
3
Low Pressure (LPDC)
3
High Pressure (HPDC)
n
| Castability Property | Rating | Explanation |
|---|---|---|
| Fluidity | 3 — Good | Good fluidity from eutectic Si level. Near-eutectic composition aids thin-wall fill. |
| Resistance to hot tearing | 4 — Excellent | Good resistance to hot tearing from the eutectic Si base. |
| Pressure tightness | 2 — Fair | Moderate pressure tightness. Complex multi-phase microstructure can create porosity paths. |
| Machinability (as-cast) | 2 — Fair | Group 2 machinability. High Si plus Ni compounds require carbide or diamond tooling. |
Heat Treatment
LM13 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.
Hardness Testing Mandatory — BS 1490 Clause 5.3.2
Unlike most LM alloys where hardness is a guideline, BS 1490 mandates hardness testing for every heat treatment batch of LM13 castings. Brinell hardness must fall within the range specified in Table 5 for the relevant condition. This is verified in-house at Creative Alucast using the FIE digital Brinell tester on every batch before despatch.
Applications
Typical Applications of LM13
| Industry | Typical Parts | Why LM13 |
|---|---|---|
| Automotive | Internal combustion engine pistons, cylinder liners, valve seats | Primary piston alloy — designed for elevated temperature service |
| Industrial Engines | Diesel engine pistons, compressor pistons, high-temperature valve bodies | Strength retention above 200°C |
| Power Generation | Generator pistons, high-temp housings, thermal components | Elevated temperature strength + low expansion |
Engine Pistons
Cylinder Liners
Valve Seats
Diesel Pistons
Compressor Pistons
High-Temperature Housings
Thermal Components
When NOT to Specify LM13
Do not specify LM13 for general engineering applications — it is a specialist elevated-temperature alloy that costs more and requires more complex quality control than general-purpose alloys. For standard structural applications use LM25. LM13 is not recommended for HPDC.
Frequently Asked Questions
Common Questions About LM13
What is the chemical composition of LM13 aluminium alloy?
LM13 per BS 1490:1988 has nominal composition Al-Si12Cu1Mg1. Silicon: 10.0–13.0%, Copper: 0.7–1.5%, Magnesium: 0.8–1.5%. The remainder is aluminium with controlled impurity limits.
What is the EN 1706 / European equivalent of LM13?
The EN 1706 equivalent of BS 1490 LM13 is EN AC-48000, with chemical symbol designation EN AC-Al Si12CuNiMg. This European standard supersedes the German DIN designation G-AlSi12CuMgNi.
What is the ASTM / AA equivalent of LM13?
The ASTM/Aluminium Association equivalent of LM13 is —. No direct ASTM equivalent.
What is the JIS equivalent of LM13?
There is no direct JIS H 5302 equivalent for LM13. No direct JIS equivalent.
What is the tensile strength of LM13?
The minimum tensile strength of LM13 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 LM13 be heat treated to T6?
Yes — LM13 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 LM13?
Per BS 1490:1988 Table 8: Sand casting (3), Gravity Die Casting (3), Low Pressure Die Casting (3), High Pressure Die Casting (n). Scale: 4=Excellent, 3=Good, 2=Fair, n=Not recommended.
What is the density of LM13 aluminium alloy?
The density of LM13 is 2.70 g/cm³ — approximately one-third the density of steel (7.85 g/cm³), making it ideal for lightweight structural applications.