BS 1490 · Group C · Special Purpose — Limited Application
lm29
Aluminium Alloy
Al-Si23Cu1Mg1Ni1 — Highest Silicon in LM Series — Minimum Thermal Expansion
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-Si23Cu1Mg1Ni1
- 22.0–25.0 %
- 2.66 g/cm³
- 190 N/mm²
- 575–520 °C
- 109 W/m·K
- 120–145 (TE and TF — mandatory) HB
Overview
Highest Silicon in LM Series — Minimum Thermal Expansion
LM29 has the highest silicon content (22–25%) of any alloy in the BS 1490 LM-series, making it the most extreme hypereutectic piston alloy. At this silicon level, the alloy has the lowest coefficient of thermal expansion (×10⁻⁶/K = 18), the highest wear resistance, and the best retention of strength at very high temperatures — at the cost of extremely difficult machinability and complex casting requirements.
LM29 shares the mandatory metallographic requirements of LM28 and is used almost exclusively for the most demanding piston applications in high-performance aviation and racing engines where LM28 does not provide sufficient wear resistance or where piston-to-bore clearance must be minimised to the absolute minimum.
Most Restrictive Alloy in BS 1490 — Specialist Use Only
LM29 requires mandatory microstructure control (same as LM28), mandatory hardness testing, diamond machining, and experienced foundry practice. It is a Group C alloy of the most limited application. Confirm requirements and foundry capability thoroughly before specifying.
Chemical Composition
LM29 Chemical Composition — BS 1490:1988
| ELEMENT | SYMBOL | MIN % | MAX % | ROLE IN ALLOY |
|---|---|---|---|---|
| Silicon | Si | 22.0 | 25.0 | 22–25% Si — the highest silicon content of any LM alloy. Extreme hypereutectic composition with very high primary silicon crystal content. Delivers minimum thermal expansion and maximum wear resistance. |
| Copper | Cu | 0.8 | 1.3 | 0.8–1.3% Cu — contributes to elevated temperature strength. |
| Magnesium | Mg | 0.8 | 1.3 | 0.8–1.3% Mg — contributes to complex precipitation system with Ni. |
| Iron | Fe | — | 0.7 | Controlled to ≤0.7% — relatively tight limit for a complex alloy. |
| Manganese | Mn | — | 0.6 | Impurity limit. Controlled to maintain clean melt. |
| Nickel | Ni | 0.8 | 1.3 | Impurity limit. |
| Zinc | Zn | — | 0.2 | 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
LM29 Equivalent Grades — International Standards
BS 1490
LM29
Group C · Special Purpose — Limited Application Al-Si23Cu1Mg1Ni1
EN 1706
—
EN AC-Al Si23Cu1Ni1Mg
ASTM / AA
—
No ASTM equivalent
JIS H 5302
—
No JIS equivalent
DIN 1725-2
G-AlSi23CuMgNi
Approximate — no current standard
ISO 3522
Al-Si23CuNiMg
ISO casting alloy designation
Mechanical Properties
LM29 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 | 190 | — | — | 100–140 |
| TF | Chill / GDC | 190 | — | — | 100–140 |
Physical Properties
LM29 Physical & Thermal Properties
Density
2.66 g/cm³
Approx. 1/3 the density of steel
Freezing Range
575–520 °C
Solidification temperature range
Thermal Conductivity
109 W/m·K
Heat dissipation capability
Electrical Conductivity
— % IACS
Relative to copper standard
Linear Expansion
18 ×10⁻⁶/K
20–300°C range
Brinell Hardness
120–145 (TE and TF — mandatory) HB
As-cast or stated condition
| PROPERTY | RATING | NOTES |
|---|---|---|
| Corrosion resistance | Fair (C) | Used in internal engine applications — corrosion resistance is secondary to thermal performance. |
| Decorative anodising | Poor (D) | Not applicable for anodising. |
| Weldability | Poor | Hypereutectic Si — not weldable. |
| Machinability group | 1 — Very Difficult | Group 1 — most difficult to machine of all LM alloys. Diamond tooling mandatory. |
Casting Suitability
LM29 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
1
Gravity Die Casting (GDC)
2
Low Pressure (LPDC)
1
High Pressure (HPDC)
n
| CASTABILITY PROPERTY | RATING | EXPLANATION |
|---|---|---|
| Fluidity | 2 — Fair | Extreme Si level creates significant castability challenges. |
| Resistance to hot tearing | 3 — Good | High Si contributes to hot-tear resistance. |
| Pressure tightness | 2 — Fair | Moderate pressure tightness. |
| Machinability (as-cast) | 1 — Very Difficult | Group 1 — most difficult to machine of all LM alloys. Diamond tooling mandatory. |
Heat Treatment
LM29 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.
Mandatory Hardness and Microstructure Testing
Both microstructure and hardness testing are mandatory for LM29 per BS 1490. TE and TF hardness ranges are 100–140 HB — the highest mandatory hardness specification in the standard. Diamond machining is the only practical tooling approach.
Applications
Typical Applications of LM29
| INDUSTRY | TYPICAL PARTS | WHY LM13 |
|---|---|---|
| Aviation | Aircraft piston engine pistons, high-speed rotating components | Minimum thermal expansion at very high temperatures |
| Racing | Extreme-performance racing engine pistons | Maximum wear resistance + minimum expansion |
Aviation Pistons
Racing Pistons
High-Speed Components
Extreme-Temperature Parts
When NOT to Specify LM29
Do not specify LM29 unless LM28 has been evaluated and found insufficient. This is the most restrictive alloy in the BS 1490 series. For all general elevated-temperature applications, LM13 or LM26 are more practical.
Frequently Asked Questions
Common Questions About LM29
What is the chemical composition of LM29 aluminium alloy?
LM29 per BS 1490:1988 has nominal composition Al-Si23Cu1Mg1Ni1. Silicon: 22.0–25.0%, Copper: 0.8–1.3%, Magnesium: 0.8–1.3%. The remainder is aluminium with controlled impurity limits.
What is the EN 1706 / European equivalent of LM29?
The EN 1706 equivalent of BS 1490 LM29 is —, with chemical symbol designation EN AC-Al Si23Cu1Ni1Mg. This European standard supersedes the German DIN designation G-AlSi23CuMgNi.
What is the ASTM / AA equivalent of LM29?
The ASTM/Aluminium Association equivalent of LM29 is —. No ASTM equivalent.
What is the JIS equivalent of LM29?
There is no direct JIS H 5302 equivalent for LM29. No JIS equivalent.
What is the tensile strength of LM29?
The minimum tensile strength of LM29 is 190 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 LM29 be heat treated to T6?
Yes — LM29 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 LM29?
Per BS 1490:1988 Table 8: Sand casting (1), Gravity Die Casting (2), Low Pressure Die Casting (1), High Pressure Die Casting (n). Scale: 4=Excellent, 3=Good, 2=Fair, n=Not recommended.
What is the density of LM29 aluminium alloy?
The density of LM29 is 2.66 g/cm³ — approximately one-third the density of steel (7.85 g/cm³), making it ideal for lightweight structural applications.