BS 1490 · Group b · Special Purpose
lm5
Aluminium Alloy
Al-Mg5Mn0.5 — The Best Corrosion Resistance in the LM Series
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-Mg5Mn0.5
- ≤0.30 %
- 2.65 g/cm³
- 170 N/mm²
- 640–600 °C
- 121 W/m·K
- 55–70 HB
Overview
The Best Corrosion Resistance in the LM Series
LM5 is the only major aluminium casting alloy in BS 1490 that contains no silicon as a primary alloying element. Its Al-Mg5Mn composition relies entirely on magnesium (3–6%) for strengthening, delivering the highest corrosion resistance and the best decorative anodising capability of any alloy in the series. It is the preferred choice for marine, food processing, and decorative applications.
The absence of silicon means LM5 has a wider freezing range and is more difficult to cast than Al-Si alloys — it requires higher pouring temperatures, more careful gating, and controlled cooling to avoid hot tearing and oxide inclusion. Good foundry practice is essential. LM5 is not heat-treatable to T6; its strength cannot be significantly improved beyond the as-cast (M) condition.
Excellent Corrosion Resistance — Best Decorative Anodising
LM5 is the first-choice alloy when the casting will be exposed to marine environments, seawater, salt spray, or when bright decorative anodising is required. Its low Cu content (≤0.10%) preserves maximum corrosion resistance. For colour anodising where appearance is critical, no other LM-series alloy performs comparably.
Chemical Composition
LM5 Chemical Composition — BS 1490:1988
| Element | Symbol | Min % | Max % | Role in alloy |
|---|---|---|---|---|
| Silicon | Si | — | 0.30 | Kept to a strict maximum of 0.3% — silicon is an impurity in LM5, not an alloying element. Higher Si would impair corrosion resistance and anodising quality. |
| Copper | Cu | — | 0.10 | Strict impurity limit ≤0.10%. Copper is the element most damaging to both corrosion resistance and decorative anodising in aluminium alloys. LM5 is specifically designed to exclude Cu. |
| Magnesium | Mg | 3.0 | 6.0 | 3–6% Mg is the primary strengthening element. Higher Mg increases strength and corrosion resistance. The wide range allows the alloy to be used in as-cast condition across different strength requirements. |
| Iron | Fe | — | 0.6 | Controlled to ≤0.6%. In Al-Mg alloys without Si, Fe forms coarse Al₃Fe particles that impair ductility. Tight control is essential. |
| Manganese | Mn | 0.3 | 0.7 | Impurity limit. Controlled to maintain clean melt. |
| Nickel | Ni | — | 0.1 | Impurity limit. |
| Zinc | Zn | — | 0.1 | Impurity limit. Higher Zn increases hot-cracking risk. |
| Lead | Pb | — | 0.05 | Impurity limit. |
| Tin | Sn | — | 0.05 | 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
LM5 Equivalent Grades — International Standards
BS 1490
LM5
Group B · Special Purpose Al-Mg5Mn0.5
EN 1706
EN AC-51300
EN AC-Al Mg5
ASTM / AA
518.0
Al-Mg8 die casting alloy — closest US equivalent
JIS H 5302
ADC5
Al-Mg series — corrosion-resistant die casting alloy
DIN 1725-2
G-AlMg5
Superseded by EN 1706
ISO 3522
Al-Mg5
ISO casting alloy designation
Mechanical Properties
LM5 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 | — | 3 | 55–65 |
| M | Chill / GDC | 170 | — | 5 | 60–70 |
Physical Properties
LM5 Physical & Thermal Properties
Density
2.65 g/cm³
Approx. 1/3 the density of steel
Freezing Range
640–600 °C
Solidification temperature range
Thermal Conductivity
121 W/m·K
Heat dissipation capability
Electrical Conductivity
31 % IACS
Relative to copper standard
Linear Expansion
24 ×10⁻⁶/K
20–300°C range
Brinell Hardness
55–70 HB
As-cast or stated condition
| Property | Rating | Notes |
|---|---|---|
| Corrosion resistance | Excellent (A) | Best corrosion resistance of any LM alloy. Zero copper, low iron. Suitable for marine, chemical, and food environments. |
| Decorative anodising | Excellent (A) | Best decorative anodising in the LM series. Bright, uniform colour achievable. Suitable for architectural and decorative applications. |
| Weldability | Good | Weldable using 5% Mg filler rod. Low Si means no eutectic weld pool issues. |
| Machinability group | 4 — Excellent | Group 4 — easiest to machine in the LM series. No hard Si particles to cause tool wear. Excellent surface finish achievable. |
Casting Suitability
LM5 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
2
Gravity Die Casting (GDC)
2
Low Pressure (LPDC)
2
High Pressure (HPDC)
2
| Castability Property | Rating | Explanation |
|---|---|---|
| Fluidity | 2 — Fair | No Si means poor fluidity compared to Al-Si alloys. Higher pouring temperatures and careful gating essential. |
| Resistance to hot tearing | 2 — Fair | Wide freezing range and no Si means higher hot-tear risk. Requires careful mould design and controlled solidification. |
| Pressure tightness | 1 — Poor | Lowest pressure tightness in the LM series. Oxide inclusions from Mg oxidation can create leak paths. Not recommended for pressure-tight applications. |
| Machinability (as-cast) | 4 — Excellent | Group 4 — easiest to machine in the LM series. No hard Si particles to cause tool wear. Excellent surface finish achievable. |
Heat Treatment
LM5 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
LM5 cannot be heat-treated to T6 or any precipitation-hardening condition. The alloy contains no Cu or sufficient Mg-Si combination to form strengthening precipitates. The only available condition is M (as-cast). Strength cannot be improved beyond 140–170 N/mm². If higher strength is required alongside corrosion resistance, consider LM31 (Al-Zn5Mg).
Applications
Typical Applications of LM5
| Industry | Typical Parts | Why LM5 |
|---|---|---|
| Marine | Boat fittings, propellers, marine hardware, saltwater pump bodies | Best corrosion resistance in LM series — survives marine atmosphere without coating |
| Food & Chemical | Processing equipment, food machinery, chemical plant fittings | No Cu contamination, corrosion resistant, cleanable |
| Decorative | Architectural fittings, decorative hardware, display components | Best decorative anodising of any LM alloy — bright, uniform colour possible |
| Agricultural | Outdoor equipment, irrigation fittings, agricultural machinery | Weather resistance without painting required |
Marine Fittings
Boat Hardware
Propellers
Chemical Plant
Food Processing Equipment
Architectural Fittings
Decorative Hardware
Outdoor Equipment
Saltwater Pumps
Irrigation Fittings
When NOT to Specify LM5
Do not specify LM5 when: (1) pressure tightness is required — LM5 rates 1 (Poor); use LM6 or LM25; (2) high strength is required — maximum tensile is 170 N/mm² with no T6 option; (3) complex thin-wall castings are needed — poor fluidity makes intricate shapes difficult; (4) high production volumes are required — casting difficulty adds cost.
Frequently Asked Questions
Common Questions About LM5
What is the chemical composition of LM5 aluminium alloy?
LM5 per BS 1490:1988 has nominal composition Al-Mg5Mn0.5. Silicon: —–0.30%, Copper: —–0.10%, Magnesium: 3.0–6.0%. The remainder is aluminium with controlled impurity limits.
What is the EN 1706 / European equivalent of LM5?
The EN 1706 equivalent of BS 1490 LM5 is EN AC-51300, with chemical symbol designation EN AC-Al Mg5. This European standard supersedes the German DIN designation G-AlMg5.
What is the ASTM / AA equivalent of LM5?
The ASTM/Aluminium Association equivalent of LM5 is 518.0. Al-Mg8 die casting alloy — closest US equivalent.
What is the JIS equivalent of LM5?
The JIS H 5302 equivalent of LM5 is ADC5. Al-Mg series — corrosion-resistant die casting alloy.
What is the tensile strength of LM5?
The minimum tensile strength of LM5 is 170 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 LM5 be heat treated to T6?
No — LM5 is not normally heat-treated to T6. Available conditions: M.
What casting processes are suitable for LM5?
Per BS 1490:1988 Table 8: Sand casting (2), Gravity Die Casting (2), Low Pressure Die Casting (2), High Pressure Die Casting (2). Scale: 4=Excellent, 3=Good, 2=Fair, n=Not recommended.
What is the density of LM5 aluminium alloy?
The density of LM5 is 2.65 g/cm³ — approximately one-third the density of steel (7.85 g/cm³), making it ideal for lightweight structural applications.