BS 1490 · Group A · General Purpose
LM20
Aluminium Alloy
Al-Si12 (higher Fe) — The HPDC-Optimised Eutectic Alloy
Sand Casting
Gravity Die Casting
Low Pressure Die Casting
High Pressure Die Casting
ISO 9001:2015
At a Glance
- Nominal composition
- Si content
- Density
- Best tensile (min)
- Freezing range
- Thermal conductivity
- Hardness
- Al-Si12 (higher Fe)
- 10.0–13.0 %
- 2.65 g/cm³
- 190 N/mm²
- 575–565 °C
- 121 W/m·K
- 50–60 HB
Overview
The HPDC-Optimised Eutectic Alloy
LM20 shares the eutectic Al-Si12 composition of LM6 but with a higher permitted iron content (up to 1.0% vs 0.6% for LM6), making it specifically optimised for high-pressure die casting where higher Fe is needed to reduce die soldering. LM20 is rated 4 (Excellent) for HPDC alongside its 4 rating for sand and GDC, making it one of only two alloys (with LM6) to achieve the top rating in gravity casting processes.
The higher Fe tolerance of LM20 is an intentional design choice for HPDC — in high-pressure die casting, iron reduces the tendency of the molten alloy to weld to the steel die surface (die soldering), extending tool life. Where LM6 is the preferred alloy for gravity casting processes, LM20 bridges LM6’s castability with HPDC practicality.
LM20 vs LM6 — Same Si, Different Fe Tolerance
The only meaningful compositional difference between LM20 and LM6 is iron: LM20 allows up to 1.0% Fe while LM6 limits Fe to 0.6%. For sand and GDC applications, LM6 is preferred (lower Fe = better ductility). For HPDC, LM20 is preferred (higher Fe = less die soldering). Both alloys are at the eutectic composition and share excellent fluidity and hot-tear resistance.
Chemical Composition
LM20 Chemical Composition — BS 1490:1988
| Element | Symbol | Min % | Max % | Role in alloy |
|---|---|---|---|---|
| Silicon | Si | 10.0 | 13.0 | 10–13% Si – eutectic composition. Same Si range as LM6, giving identical fluidity and hot-tear resistance benefits. |
| Copper | Cu | — | 0.40 | Up to 0.40% Cu. Slightly higher than LM6 (0.10%) – reduces corrosion resistance somewhat but acceptable for HPDC applications. |
| Magnesium | Mg | — | 0.20 | Impurity limit ≤0.20%. LM20 is not heat-treatable. |
| Iron | Fe | — | 1.0 | Up to 1.0% Fe – the key differentiator from LM6. Higher Fe is essential in HPDC to prevent die soldering. In sand and GDC, keep Fe as low as possible within this limit. |
| Manganese | Mn | — | 0.5 | Impurity limit. Controlled to maintain clean melt. |
| Nickel | Ni | — | 0.1 | 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
LM20 Equivalent Grades — International Standards
BS 1490
LM20
Group A · General Purpose Al-Si12 (higher Fe)
EN 1706
EN AC-44300
EN AC-Al Si12(Fe)
ASTM / AA
A413.0
A413.0 — primary US equivalent for HPDC eutectic alloy
JIS H 5302
ADC1
Al-Si12 — standard HPDC eutectic alloy
DIN 1725-2
GD-AlSi12
Superseded by EN 1706
ISO 3522
Al-Si12(Fe)
ISO casting alloy designation
Mechanical Properties
LM20 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 | — | — | — | 50–55 |
| M | Chill / GDC | 190 | — | 5 | 55–65 |
| M | HPDC | ~220–240 | ~120 | ~1 | 65–80 |
Physical Properties
LM20 Physical & Thermal Properties
Density
2.65 g/cm³
Approx. 1/3 the density of steel
Freezing Range
575–565 °C
Solidification temperature range
Thermal Conductivity
121 W/m·K
Heat dissipation capability
Electrical Conductivity
— % IACS
Relative to copper standard
Linear Expansion
20 ×10⁻⁶/K
20–300°C range
Brinell Hardness
50–60 HB
As-cast or stated condition
| Property | Rating | Notes |
|---|---|---|
| Corrosion resistance | Fair (D) | Higher Fe and Cu than LM6 reduce corrosion resistance. Not suitable for marine use. |
| Decorative anodising | Poor (D) | High Si and Fe give poor anodised appearance. |
| Weldability | Good | Weldable using 10% Si filler rod. Low Cu content prevents hot cracking. |
| Machinability group | 1 — Difficult | Group 1 — high Si causes tool wear. Same machinability challenge as LM6. Carbide tooling required. |
Casting Suitability
LM20 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)
4
High Pressure (HPDC)
4
| Castability Property | Rating | Explanation |
|---|---|---|
| Fluidity | 4 — Excellent | Eutectic composition — identical fluidity advantage to LM6. |
| Resistance to hot tearing | 4 — Excellent | Eutectic solidification eliminates the mushy zone where hot tears form. |
| Pressure tightness | 4 — Excellent | Excellent pressure tightness from eutectic solidification. Suitable for pressure-tight HPDC components. |
| Machinability (as-cast) | 1 — Difficult | Group 1 — high Si causes tool wear. Same machinability challenge as LM6. Carbide tooling required. |
Heat Treatment
LM20 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.
Not Heat-Treatable — As-Cast or Stress Relief Only
LM20 cannot be T6 heat-treated. The alloy contains no Mg or Cu in sufficient quantities for precipitation hardening. Only M (as-cast) and TS (stress relieve 200–250°C) are applicable conditions. If T6 strength is required from a eutectic-Si alloy, specify LM9 instead.
Applications
Typical Applications of LM20
| Industry | Typical Parts | Why LM13 |
|---|---|---|
| Automotive | Thin-wall engine covers, HPDC housings, complex inlet manifolds | Eutectic castability for complex HPDC geometry |
| Electrical | HPDC motor housings, generator parts, electrical enclosures | Good HPDC surface finish, complex shapes |
| Consumer | High-volume HPDC consumer products, hardware | Cost-effective HPDC in high volumes |
Thin-Wall HPDC
Engine Brackets
HPDC Housings
Motor Housings
Electrical Enclosures
High-Volume Parts
Complex HPDC
When NOT to Specify LM20
Do not specify LM20 for gravity (GDC/LPDC) applications when LM6 is available — LM6’s lower Fe limit gives better ductility. Do not specify when T6 is required — use LM9. Do not specify when decorative anodising is required.
Frequently Asked Questions
Common Questions About LM20
What is the chemical composition of LM20 aluminium alloy?
LM20 per BS 1490:1988 has nominal composition Al-Si12 (higher Fe). Silicon: 10.0–13.0%, Copper: —–0.40%, Magnesium: —–0.20%. The remainder is aluminium with controlled impurity limits.
What is the EN 1706 / European equivalent of LM20?
The EN 1706 equivalent of BS 1490 LM20 is EN AC-44300, with chemical symbol designation EN AC-Al Si12(Fe). This European standard supersedes the German DIN designation GD-AlSi12.
What is the ASTM / AA equivalent of LM20?
The ASTM/Aluminium Association equivalent of LM20 is A413.0. A413.0 — primary US equivalent for HPDC eutectic alloy.
What is the JIS equivalent of LM20?
The JIS H 5302 equivalent of LM20 is ADC1. Al-Si12 — standard HPDC eutectic alloy.
What is the tensile strength of LM20?
The minimum tensile strength of LM20 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 LM20 be heat treated to T6?
No — LM20 is not normally heat-treated to T6. Available conditions: M, TS.
What casting processes are suitable for LM20?
Per BS 1490:1988 Table 8: Sand casting (4), Gravity Die Casting (4), Low Pressure Die Casting (4), High Pressure Die Casting (4). Scale: 4=Excellent, 3=Good, 2=Fair, n=Not recommended.
What is the density of LM20 aluminium alloy?
The density of LM20 is 2.65 g/cm³ — approximately one-third the density of steel (7.85 g/cm³), making it ideal for lightweight structural applications.