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LM27

Aluminium Casting Alloy LM27

This alloy conforms to BS 1490:1988 LM27.

Chemical Composition

  %   %   %
 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 Properties

 

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 (x103 N/mm2)

71

71

Shear Strength (N/mm2)

-

-

Strength at elevated temperatures

LM27 retains a high proportion of its original room temperature strength at moderately elevated temperatures. For short period exposure, the tensile strength of gravity die castings is reduced by only 20% at 200°C and by 40% at 250°C. The reduction in proof stress is considerably less.

Physical properties

 

 

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

Machinability

LM27 has fairly good machining characteristics and is similar in this respect to LM4-M. For the best results, tungsten carbide tools are recommended. Liberal use of cutting lubricant and coolant is advised.

Corrosion Resistance

Resistance to attack under normal atmospheric conditions is fairly good.

Anodising

Treatment by the more common processes produces a protective surface with a greyish opaque film. Anodising for decorative purposes is generally impracticable for the depth of anodic coating required to ensure adequate durability.

Heat Treatment

This alloy is standardised in the as cast condition, but it has been shown that the tensile properties may be substantially increased by appropriate heat treatment.

Applications and General Notes

LM27 is a very versatile alloy and, with its excellent castability, is suitable for most general purpose castings where moderate mechanical properties are desirable, such as general engineering components, domestic and office equipment, household fittings, electrical tools and switch gear, automobile engine and transmission components.

It is equally suitable for sand and gravity die castings of thick or thin sections, and for castings required to be pressure tight. In short, it can be used with the advantage of slightly superior castability for the all the kinds of application for which LM4 is used and may be expected, in time, to supersede the older alloy.

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