BS 1490 · Group A · General Purpose

LM6 Aluminium Alloy

Al-Si12 — The most castable alloy in the LM series — a strong fit for our sand casting process

Nominal composition

Al-Si12

Silicon content

10.0–13.0%

Density

2.65 g/cm³

Best tensile (min)

190 N/mm²

Freezing range

575–565°C

Thermal conductivity

150 W/m·K

Hardness

50–60 HB

Overview

The most castable alloy in the LM series — a strong fit for our sand casting process

LM6 sits right at the eutectic point of the aluminium-silicon system — around 12.6% silicon — which is what gives it a single, narrow solidification temperature rather than a wide freezing range. Practically, that means outstanding fluidity, minimal shrinkage, and the ability to fill thin, intricate sections that other alloys would struggle with.

It's also the most corrosion-resistant of the general-purpose Group A alloys, thanks to its very low copper content, which makes it a sound choice for marine and mild chemical environments. The trade-off is machinability — the high silicon content wears tooling quickly — and limited scope for strengthening through heat treatment beyond a basic stress relief.

Chemical Composition

LM6 Chemical Composition — BS 1490:1988

Element	Symbol	Min %	Max %	Role in Alloy
Silicon	Si	10.0	13.0	Sits at the Al-Si eutectic (12.6%), giving minimum freezing range, maximum fluidity, and the fine grain structure behind LM6's exceptional castability.
Copper	Cu	—	0.10	Kept very low — the defining feature that preserves LM6's corrosion resistance for marine and food-grade use.
Magnesium	Mg	—	0.10	Impurity limit — too low to support precipitation hardening.
Iron	Fe	—	0.6	Controlled to limit brittle β-AlFeSi platelets that can reduce ductility.
Manganese	Mn	—	0.5	Impurity limit, controlled for melt cleanliness.
Nickel	Ni	—	0.1	Impurity limit.
Zinc	Zn	—	0.1	Impurity limit — higher Zn raises hot-cracking risk.
Lead	Pb	—	0.1	Impurity limit.
Tin	Sn	—	0.05	Impurity limit.
Titanium	Ti	—	0.2	Added as a grain refiner (typically TiB₂ master alloy).
Aluminium	Al	—	Remainder	Base metal.
Other elements	—	—	0.05 each / 0.15 total	Each unlisted element capped individually and in total.

Global Standards

LM6 Equivalent Grades — International Standards

Mechanical Properties

LM6 Mechanical Properties — BS 1490:1988 Table 4

Minimum values from separately cast test samples. These are guaranteed minimums, not averages — properties in an actual casting 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	160	—	5	50–55
M	Chill / GDC	190	—	7	55–65
TS	Any	~160	—	~4	50–55

Physical Properties

LM6 Physical & Thermal Properties

Working Properties

Corrosion, Finishing & Machining

Corrosion resistance

Good

The best of the Group A alloys — low copper (≤0.10%) suits marine atmospheres and mild chemical exposure.

Decorative anodising

Fair

Silicon gives a grey-black anodised finish — fine for protective anodising, not for bright decorative work.

Weldability

Excellent

The best-welding alloy in the LM series; a 10% Si filler rod is typically recommended.

Machinability

Difficult

The hardest to machine in the LM series — high silicon wears tooling quickly; carbide or diamond tooling is advised.

Casting Suitability

LM6 Casting Process Suitability — BS 1490:1988 Table 8

Scale: 4 = Excellent, 3 = Good, 2 = Fair, 1 = Poor, n = possible but not normally recommended.

Sand Casting

Gravity Die Casting

Low Pressure Die Casting

High Pressure Die Casting

Heat Treatment

LM6 Heat Treatment — BS 1490:1988 Conditions

LM6 can't be taken to T6 — there isn't enough copper or magnesium present for precipitation hardening. Stress relief (TS, 200–250°C) is the only routine treatment, applied to settle residual casting stress ahead of precision machining. Where strength beyond 190 N/mm² is needed, LM25 is usually the better-suited alloy — it offers comparable castability with full T6 capability.

Applications

Typical Applications of LM6

Frequently Asked Questions

Common Questions About LM6

What is the chemical composition of LM6?

Per BS 1490:1988, LM6 has a nominal composition of Al-Si12 — Silicon 10.0–13.0%, Copper up to 0.10%, Magnesium up to 0.10%, with the balance aluminium and controlled impurity limits.

What is the European (EN 1706) equivalent of LM6?

EN AC-44100 (EN AC-Al Si12(b)), which supersedes the older German DIN designation G-AlSi12.

What is the ASTM equivalent of LM6?

413.0 / A413.0 is the primary US equivalent.

Can LM6 be heat treated to T6?

No — only stress relief (TS) is routinely applied to this alloy.

Which casting processes suit LM6?

Per BS 1490 Table 8: Sand casting, Gravity Die Casting, and Low Pressure Die Casting are all rated 4 (Excellent); High Pressure Die Casting is rated 3 (Good).

What is the density of LM6?

2.65 g/cm³ — roughly a third the density of steel.

Other alloys:LM2 LM25

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