Aluminium Die Casting Alloy LM25
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LM25 ALUMINIUM CASTING ALLOY SUMMARY
MRT produces gravity die castings, sand castings, and high-pressure die castings in LM25 aluminium alloy.
One of the key reasons for selecting LM25 is the notable strength achievable in the heat-treated condition. Although heat treatment is not typically used for high-pressure die castings, LM25 is most commonly chosen for gravity or sand casting.
This alloy complies with BS 1490:1988 LM25. Castings are supplied in the as-cast (M) state, the precipitation-treated (TE) condition, the solution-treated and stabilised (TB7) form, and the fully heat-treated (TF) condition.
CHEMICAL MAKEUP
| % | % | % | |||
|---|---|---|---|---|---|
| Copper | 0.20 max | Magnesium | 0.20–0.6 | Silicon | 6.5–7.50 |
| Iron | 0.5 | Manganese | 0.3 max | Nickel | 0.1 max |
| Zinc | 0.1 max | Lead | 0.1 max | Tin | 0.05 max |
| Titanium | 0.2 max | Aluminium | Remainder | Others each | 0.05 max |
| Others total | 0.15 max |
MECHANICAL PERFORMANCE
| LM25-M | LM25-TE | LM25-TB7 | LM25-TF | |||||
|---|---|---|---|---|---|---|---|---|
| Sand | Gravity | Sand | Gravity | Sand | Gravity | Sand | Gravity | |
| 0.2% Proof Stress (N/mm²) | 80–100 | 80–100 | 120–150 | 130–200 | 80–110 | 90–110 | 200–250 | 220–260 |
| Tensile Strength (N/mm²) | 130–150 | 160–200 | 150–180 | 190–250 | 160 | 230 | 230–280 | 280–320 |
| Elongation (%) | 2 | 3 | 1 | 2 | 2.5 | 5 | - | 2 |
| Impact Resistance Izod (Nm) | - | - | - | - | - | - | - | - |
| Brinell Hardness | 55–65 | 55–65 | 70–75 | 75–95 | 65–75 | 65–75 | 90–110 | 90–110 |
| Modulus of Elasticity (×10³ N/mm²) | 71 | 71 | 71 | 71 | 71 | 71 | 71 | 71 |
| Shear Strength (N/mm²) | - | - | 140 | - | - | - | 180 | 250 |
HIGH-TEMPERATURE BEHAVIOUR
The elevated-temperature properties of LM25 depend on the casting’s heat-treatment condition.
In short-term exposure (e.g., 30 minutes), LM25 retains strength uniformly up to 230°C, after which the tensile strength of LM25-TF drops to roughly 25% (approx. 90 MPa).
Longer exposure—such as 10,000 hours—causes a marked strength decline around 135°C.
At 200°C, the strength of LM25-TF is about half of its room-temperature value.
Heat treatment offers little benefit if the component must operate at temperatures above roughly 130°C for prolonged periods.
PHYSICAL CHARACTERISTICS
| Coefficient of Thermal Expansion (per °C @ 20–100°C) | 0.000022 |
| Thermal Conductivity (cal/cm²/cm/°C @ 25°C) | 0.36 |
| Electrical Conductivity (% copper standard @ 20°C) | 39 |
| Density (g/cm³) | 2.68 |
| Freezing Range (°C) approx. | 615–550 |
MACHINING QUALITIES OF LM25
In the heat-treated state, LM25 machines reasonably well, though tools—preferably high-speed steel—must remain sharp. A moderate rate of tool wear can be expected. Ample lubrication should be used. (See MRT’s machining resources for more information.)
RESISTANCE TO CORROSION
Similar to LM6, LM25 provides strong resistance to both seawater and marine atmospheres.
ANODISING SUITABILITY
Chromic or sulphuric acid anodising produces a protective anodic coating.
However, the natural grey appearance of LM25 castings may affect final colouring if a decorative finish is required. (MRT provides additional details on anodising options.)
HEAT TREATMENT
LM25 is commonly supplied in three heat-treatment states: LM25-TE (precipitation treated), TB7 (solution-treated and stabilised), and TF (fully heat-treated). MRT provides full details of these processes.
USES AND PRACTICAL NOTES
LM25 is typically chosen where strong mechanical performance is required in castings of complex geometry or in applications that demand a high level of structural integrity.
Because of its strong corrosion resistance, LM25 is used widely in marine environments and chemical plants.
Its toughness makes it suitable for water-cooled cylinder heads, valve bodies, air-compressor pistons, wheels, cylinder blocks, vehicle suspensions, and transport equipment.
The alloy also performs well in both sand-casting and gravity die-casting applications.
Where optimum strength is needed, LM25 is used in the fully heat-treated condition.
Overall, LM25 offers high strength, excellent corrosion resistance, and good weldability, though its fracture-toughness properties are lower than LM6.