Aluminium Casting Alloy LM27 – creativeallucast.ifbsindia.com

Aluminium Die Casting Alloy LM27

Aluminium Alloys

LM27 ALUMINIUMCASTING ALLOY SUMMARY

This alloy complies with BS 1490:1988 LM27.

CHEMICAL MAKEUP

	%		%		%
Copper	1.5–2.5	Magnesium	0.35 max	Silicon	6.0–8.0
Iron	0.5 max	Manganese	0.2–0.6	Nickel	0.3 max
Zinc	1.0 max	Lead	0.2 max	Tin	0.1 max
Titanium	0.2 max	Aluminium	Remainder	Others each	0.05 max
Others total	0.15 max

MECHANICAL PERFORMANCE

	SAND CASTING	GRAVITY DIE CASTING
0.2% Proof Stress (N/mm²)	80–90	90–110
Tensile Strength (N/mm²)	140	160
Elongation (%)	1	2
Impact Resistance Izod (Nm)	-	-
Brinell Hardness	70–85	75–90
Modulus of Elasticity (×10³ N/mm²)	71	71
Shear Strength (N/mm²)	-	-

BEHAVIOUR AT HIGH TEMPERATURES

LM27 retains a large share of its room-temperature strength at moderately raised temperatures. Over short durations, the tensile strength of gravity-die castings falls by only about 20% at 200°C and by roughly 40% at 250°C. The loss of proof stress is somewhat smaller.

PHYSICAL CHARACTERISTICS


Coefficient of Thermal Expansion (per °C @ 20–100°C)	0.0000215
Thermal Conductivity (cal/cm²/cm/°C @ 25°C)	0.37
Electrical Conductivity (% copper standard @ 20°C)	27
Density (g/cm³)	2.75
Freezing Range (°C) approx.	605–525

MACHINING QUALITIES

LM27 machines reasonably well, similar to LM4-M. Tungsten carbide tooling is recommended for optimum results. Generous use of coolant and cutting lubricant is advised.

RESISTANCE TO CORROSION

Under typical atmospheric exposure, LM27 provides generally good resistance to corrosion.

ANODISING SUITABILITY

Standard anodising processes produce a greyish, opaque protective film. Decorative anodising is usually not recommended because the depth of coating needed for durability limits the ability to achieve uniform colouring.

HEAT TREATMENT

Although LM27 is supplied mainly in the as-cast condition, tensile properties can be significantly improved through heat treatment when required.

USES AND PRACTICAL NOTES

LM27 is a highly adaptable alloy with strong casting fluidity, making it suitable for general-purpose castings where moderate mechanical strength is acceptable. Typical uses include domestic and office equipment, household hardware, electrical fittings, switchgear, and automotive engine or transmission components.

It performs well in both sand-casting and gravity-die casting processes for thin or thick sections, and it is also suitable for pressure-tight castings. In many applications where LM4 was traditionally used, LM27 now serves as a capable, and often superior, replacement.