BS 1490 · Group B · Special Purpose
lm22
Aluminium Alloy
Al-Si5Cu3Mn0.4 — High Shock Resistance and Natural-Age Strength
Sand Casting
Gravity Die Casting
Low Pressure Die Casting
ISO 9001:2015
At a Glance
- Nominal composition
- Si content
- Density
- Best tensile (min)
- Freezing range
- Thermal conductivity
- Hardness
- Al-Si5Cu3Mn0.4
- 4.0–6.0 %
- 2.73 g/cm³
- 245 N/mm²
- 620–520 °C
- 121 W/m·K
- 80–95 (TB condition) HB
Overview
High Shock Resistance and Natural-Age Strength
LM22 is a medium-silicon, medium-copper alloy delivering high tensile strength and elongation in the TB (solution treated + naturally aged) condition. BS 1490 specifies LM22 only in the TB condition, where chill casting delivers 245 N/mm² minimum tensile with 8% elongation — an exceptional combination of strength and ductility that makes it the alloy of choice for shock-loaded structural components in heavy-duty transport and road vehicle applications.
The 8% minimum elongation in TB chill cast condition is the highest elongation specification for any heat-treated alloy in the BS 1490 series (matched only by the TB7 condition of LM25 at 5%). This ductility in a heat-treated state reflects LM22’s specific formulation for impact and fatigue resistance.
Highest Elongation in Heat-Treated Condition
LM22 TB chill cast achieves 8% minimum elongation at 245 N/mm² minimum tensile — the highest elongation specification of any heat-treated LM alloy in BS 1490. This combination of high strength and exceptional ductility is the specific design intent: components subjected to impact loading, vibration, and fatigue cycles in heavy vehicle service.
Chemical Composition
LM22 Chemical Composition — BS 1490:1988
| Element | Symbol | Min % | Max % | Role in alloy |
|---|---|---|---|---|
| Silicon | Si | 4.0 | 6.0 | 4–6% Si — same range as LM4. Provides moderate castability. Not eutectic; wider freezing range requires careful feeding in heavy sections. |
| Copper | Cu | 2.8 | 3.8 | 2.8–3.8% Cu — primary hardening agent. CuAl₂ precipitates form during natural ageing (TB condition). Narrower Cu range than LM4 for tighter TB performance control. |
| Magnesium | Mg | — | 0.05 | Very low Mg (≤0.05%). LM22 is unusual in its near-zero Mg content — TB strength comes from Cu precipitation alone, not Mg₂Si. This avoids the Mg sensitivity issues that affect T6 alloys. |
| Iron | Fe | — | 0.6 | Controlled to ≤0.6% — lower than HPDC alloys, reflecting the GDC/sand structural application. |
| Manganese | Mn | 0.2 | 0.6 | Impurity limit. Controlled to maintain clean melt. |
| Nickel | Ni | — | 0.15 | Impurity limit. |
| Zinc | Zn | — | 0.15 | Impurity limit. Higher Zn increases hot-cracking risk. |
| Lead | Pb | — | 0.1 | 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
LM22 Equivalent Grades — International Standards
BS 1490
LM22
Group B · Special Purpose Al-Si5Cu3Mn0.4
EN 1706
EN AC-45400
EN AC-Al Si5Cu3
ASTM / AA
—
No close ASTM equivalent
JIS H 5302
—
No JIS equivalent
DIN 1725-2
G-AlSi5Cu3
Superseded by EN 1706
ISO 3522
Al-Si5Cu3
ISO casting alloy designation
Mechanical Properties
LM22 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 |
|---|---|---|---|---|---|
| TB | Chill / GDC | 245 | — | 8 | 85–95 |
Physical Properties
LM22 Physical & Thermal Properties
Density
2.73 g/cm³
Approx. 1/3 the density of steel
Freezing Range
620–520 °C
Solidification temperature range
Thermal Conductivity
121 W/m·K
Heat dissipation capability
Electrical Conductivity
— % IACS
Relative to copper standard
Linear Expansion
21 ×10⁻⁶/K
20–300°C range
Brinell Hardness
80–95 (TB condition) HB
As-cast or stated condition
| Property | Rating | Notes |
|---|---|---|
| Corrosion resistance | Fair (C) | Cu content (2.8–3.8%) limits corrosion resistance. Suitable for indoor/protected environments. |
| Decorative anodising | Poor (D) | Cu content gives poor anodising quality. |
| Weldability | Fair | Weldable with care. Post-weld natural ageing required to restore TB properties. |
| Machinability group | 3 — Good | Group 3 machinability. Cu content assists chip formation. |
Casting Suitability
LM22 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 | Moderate Si gives adequate fluidity for most geometries. |
| Resistance to hot tearing | 3 — Good | Reasonable resistance. Wider freezing range requires controlled feeding. |
| Pressure tightness | 3 — Good | Good pressure tightness from correct casting practice. |
| Machinability (as-cast) | 3 — Good | Group 3 machinability. Cu content assists chip formation. |
Heat Treatment
LM22 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.
TB — Solution Treat + Natural Ageing
LM22 is specified only in the TB condition: solution treat at approximately 515°C, water quench, then naturally aged at room temperature for a minimum of several days. No artificial ageing is specified — strength develops from room-temperature CuAl₂ precipitation. Full in-house solution treatment at Creative Alucast. No artificial ageing furnace cycle required — reduces lead time.
Applications
Typical Applications of LM22
| Industry | Typical Parts | Why LM13 |
|---|---|---|
| Automotive | Suspension components, steering linkages, structural brackets, road transport castings | High strength + 8% elongation = ideal for impact and fatigue loaded parts |
| Commercial Vehicles | Heavy duty structural castings, chassis components, gearbox cases | BS 1490 specifically notes road transport vehicles as the application |
| Industrial | Shock-loaded machine components, impact-resistant brackets | Unique combination of 245 N/mm² + 8% elongation |
Suspension Components
Steering Linkages
Structural Brackets
Heavy Vehicle Parts
Chassis Components
Impact-Resistant Parts
Shock-Loaded Components
When NOT to Specify LM22
Do not specify LM22 for applications requiring corrosion resistance — high Cu reduces resistance. Do not specify for HPDC. Do not specify when artificial ageing (T6) is required — LM22 TB is natural age only.
Frequently Asked Questions
Common Questions About LM22
What is the chemical composition of LM22 aluminium alloy?
LM22 per BS 1490:1988 has nominal composition Al-Si5Cu3Mn0.4. Silicon: 4.0–6.0%, Copper: 2.8–3.8%, Magnesium: —–0.05%. The remainder is aluminium with controlled impurity limits.
What is the EN 1706 / European equivalent of LM22?
The EN 1706 equivalent of BS 1490 LM22 is EN AC-45400, with chemical symbol designation EN AC-Al Si5Cu3. This European standard supersedes the German DIN designation G-AlSi5Cu3.
What is the ASTM / AA equivalent of LM22?
The ASTM/Aluminium Association equivalent of LM22 is —. No close ASTM equivalent.
What is the JIS equivalent of LM22?
There is no direct JIS H 5302 equivalent for LM22. No JIS equivalent.
What is the tensile strength of LM22?
The minimum tensile strength of LM22 is 245 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 LM22 be heat treated to T6?
No — LM22 is not normally heat-treated to T6. Available conditions: TB.
What casting processes are suitable for LM22?
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 LM22 aluminium alloy?
The density of LM22 is 2.73 g/cm³ — approximately one-third the density of steel (7.85 g/cm³), making it ideal for lightweight structural applications.