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LM29 - Aluminium Casting Alloy

( A1-Si23Cu1Mg1Ni1 )

Colour Code - BROWN/GREEN

This alloy conforms to BS 1490:1988 LM29. Castings are standardized in the precipitation

treated (TE) condition and the fully heat treated (TF) condition.

Chemical Composition

%

Copper 0.8-1.3

Magnesium 0.8-1.3

Silicon 22-25

Iron 0.7 max

Manganese 0.6 max

Nickel 0.8-1.5

Zinc 0.2 max

Lead 0.1 max

Tin 0.1 max

Titanium 0.2 max

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%

Chronium 0.6 max

Cobalt 0.5 max

Aluminium Remainder

Others: each 0.10 max

Others: total 0.30 max

Figures in brackets are ingot compositions where they differ from the casting, single figures are

maxima.

Mechanical Properties

LM29-TE

Sand Cast Chill Cast

0.2% Proof Stress (N/mm 2 ) 120 170

Tensile Stress (N/mm 2 ) 120 190

Elongation (%) 0.5 0.5

Impact Resistance Izod (Nm) - -

Brinell Hardness 100-140 100-140

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Sand Cast Chill Cast

Endurance Limit (5x10 7cycles;N/mm 2 )

- -

Modulus of Elasticity (x10 3N/mm 2 )

88 88

Shear Strength (N/mm 2 ) - -

LM29-TF

Sand Cast Chill Cast

0.2% Proof Stress (N/mm 2 ) 120 170-190

Tensile Stress (N/mm 2 ) 120 190-220

Elongation (%) 0.5 0.5

Impact Resistance Izod (Nm) - -

Brinell Hardness 100-140 100-140

Endurance Limit (5x10 7 cycles;N/mm 2 ) - -

Modulus of Elasticity (x10 3 N/mm 2 ) 88 88

Shear Strength (N/mm 2 ) - -

The values shown are typical ranges for sand and chill cast test bars produced to the

requirement of B.S. 1490. Those in heavier type are minimum specification values.

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Strength at Elevated Temperatures

Castings in LM29 retain a high proportion of their room temperature strength and hardness at

the normal operating temperatures of internal combustion engine pistons, e.g., after heating at

200C for 1000 hours castings may be expected to have half their initial room temperaturestrength. At 300C the tensile strength is of the order of 60 N/mm 2

Physical Properties

Coefficient of Thermal Expansion (perC at 20-100C) 0.0000165

Coefficient of Thermal Expansion (perC at 20-200C) 0.000018

Thermal Conductivity (cal/cm 2 /cm/C at 25C) 0.24-0.27

Electrical Conductivity (% copper standard at 20C) -

Density (g/cm 3 ) 2.65

Freezing Range (C) approx 770-520

Machinability

This alloy and the preceding alloy LM28 have the lowest machinability rating of the Aluminium

casting alloys mainly as a result of the high proportion of Silicon they contain, which can lead to

rapid tool wear. If the alloy is not adequately refined, in addition to the rapid tool wear which will

occur, there is a danger that some of the coarse Silicon particles may be torn from the surface.

If the alloy is properly refined and the Silicon particles as a result are fine and uniformly

distributed, castings can be machined satisfactorily with frequently sharpened carbide tipped

tools, using large rake angles and relatively low cutting speeds. A cutting lubricant and coolant

should be employed. For pistons, the common practice is to use diamond tools.

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Corrosion Resistance

There is very little likelihood of corrosive attack of pistons under service conditions and the high

resistance of the alloy to atmospheric corrosion is of little practical significance.

Anodizing

LM29 can be anodized but the coating is not suitable for decorative purposes.

Casting Characteristics

FLUIDITY - Fair

PRESSURE TIGHTNESS -Fair

HOT-TEARING - Good

TYPICAL POURING TEMPERATURE - 830C

LM29 is refined with Phosphorus containing agents, or Phosphor-Copper to avoid the formationof coarse primary Silicon particles, the formation of which will cause problems in machining,segregation and brittleness. BS1490 permits a maximum primary Silicon particle size of 70microns for individual particles and an average of 40 microns for all Silicon particles.

To obtain the desired structure, a rapid rate of solidification is required so permanent mouldcasting methods are preferable to sand casting. Prolonged degassing treatment may benecessary as, at the high melt temperatures, gas pickup is considerable. Oxidation will increaseat these higher temperatures.

Flux compositions must be free of Sodium to avoid negating the modification process.

High gating ratios are recommended and metal should be poured rapidly to avoid Siliconseparation in the runners.

PATTERNMAKERS' SHRINKAGE - Tall feeders are needed to prevent shrinkage pipesextending into the casting.

Heat Treatment

For pistons, the precise details of the heat treatment employed depends to some extent on the

service conditions and the requirement for the particular piston.

LM29-TF (fully heat treated) -heat for 4 hours at 500C, quench in an air blast, followed by

precipitation hardening for 8 hours at 185C.

LM29-TE (artificially aged) - heat at 185C for a time appropriate to obtain the desired

properties.

Applications

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LM29 is used for pistons for high performance internal combustion engines where advantage

can be taken of its low coefficient of thermal expansion and its high resistance to wear.