Aluminium Casting Alloy LM9
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LM9 ALUMINIUM CASTING ALLOY SUMMARY
CHEMICAL MAKEUP
| % | % | % | |||
|---|---|---|---|---|---|
| Copper | 0.2 | Magnesium | 0.2–0.6 | Silicon | 10.0–13.0 |
| Iron | 0.6 | Manganese | 0.3–0.7 | Nickel | 0.1 max |
| Zinc | 0.1 | Lead | 0.1 max | Tin | 0.05 max |
| Titanium | 0.2 | Aluminium | Remainder | Others each | 0.05 max |
| Others total | 0.15 max |
MECHANICAL PERFORMANCE OF LM9 (SAND & DIE CASTING)
| M GRAVITY DIE CAST | TF SAND CAST | TF GRAVITY DIE CAST | TE SAND CAST | TEGRAVITY DIE CAST | |
|---|---|---|---|---|---|
| 0.2% Proof Stress (N/mm²) | 95–120 | 220–250 | 270–280 | 110–130 | 150–170 |
| Tensile Strength (N/mm²) | 190 | 240 | 295 | 170 | 230 |
| Elongation (%) | 3–5 | 0–1 | 0–1 | 1.5 | 2 |
| Impact Resistance Izod (Nm) | - | 0.7 | 1.4 | 1.4 | 2 |
| Brinell Hardness | 75–85 | 95 | 110 | 70 | 85 |
| Modulus of Elasticity (10³ N/mm²) | - | 71 | 71 | 71 | 71 |
| Shear Strength (N/mm²) | - | 200 | 230 | 120 | 160 |
HIGH-TEMPERATURE BEHAVIOUR
Tensile properties remain largely unchanged up to around 150°C, but extended exposure at higher temperatures leads to a significant drop in strength. For instance, the tensile strength of chill-cast LM9-TF at 200°C (after 500 hours of heating) is roughly half of its value at room temperature, and only about a quarter of its strength at 250°C.
PHYSICAL CHARACTERISTICS OF LM9 (SAND & DIE CASTING)
| Coefficient of Thermal Expansion (per °C @ 20–100°C) | 0.000022 |
| Thermal Conductivity (cal/cm²/cm/°C @ 25°C) | 0.35 |
| Electrical Conductivity (% copper standard @ 20°C) | 38.0 |
| Density (g/cm³) | 2.68 |
| Freezing Range (°C) approx. | 575–550 |
MACHINING QUALITIES
Machining LM9 causes substantial tool wear, though it does not exhibit the same dragging effect seen in high-silicon alloys like LM6. Using carbide tools with large rake angles and slower cutting speeds typically achieves better results. Adequate lubrication and cooling are essential.
RESISTANCE TO CORROSION
LM9 provides strong corrosion resistance under standard atmospheric and marine environments.
ANODISING SUITABILITY
LM9 accepts normal anodising processes effectively, producing protective films that range from grey to dark brown depending on the method used.
Heat Treatment
Heat treatment significantly increases both strength and hardness.
USES AND PRACTICAL NOTES
LM9 is selected where a combination of good fluidity and strong corrosion resistance—similar to LM6—is required, but with added strength and hardness. It is equally suitable for sand casting and gravity die casting and is widely used for low-pressure castings, instrument cases, cover plates, and components intended for electroplating.
The alloy, however, has poor weldability and is not easily brazed.