BSL169 - Aluminium Casting Alloy

(Al -Si7Mg0.6)   

This alloy conforms to British Standard L169. Castings are standardized in the solution treated and artificially aged condition.

Material supplied as standard 7kg aluminium ingot.

Chemical Composition

Copper 0.10 max
Magnesium 0.50-0.75
Silicon 6.5-7.5
Iron 0.15 max
Manganese 0.10 max
Nickel 0.05 max
Zinc 0.05 max
Lead 0.05 max.
Tin 0.05 max
Titanium 0.10-0.20
Berylium 0.07 max
Aluminium Remainder
Others: each 0.05 max.
Others: total 0.15 max. 

Grain refinement shall be carried out using Titanium and Boron. The release documents for ingots must state the grain refining element(s) used, if any.

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

Specific modifying elements maybe added in sufficient quantities to provide the necessary casting material quality. 

Mechanical Properties

  Sand Cast Chill Cast
0.2% Proof Stress (N/mm 2 ) 240 240
Tensile Stress (N/mm 2 ) 290 320
Elongation (%) 3.0 4.0
Impact Resistance Izod (Nm) - -
Brinell Hardness 80 85
Endurance Limit (5x10 7 cycles;N/mm 2 ) 110 110
Modulus of Elasticity (x10 3 N/mm 2 ) 72 72
Shear Strength (N/mm 2 ) - -


  Investment Cast
0.2% Proof Stress (N/mm 2 ) 240
Tensile Stress (N/mm 2 ) 300
Elongation (%) 3.5
Impact Resistance Izod (Nm) -
Brinell Hardness 80
Endurance Limit (5x10 7 cycles;N/mm 2 ) -
Modulus of Elasticity (x10 3 N/mm 2 ) 72
Shear Strength (N/mm 2 ) -

The values in bold type are standardized properties for separately cast test samples produced to the requirements of BS 4L101; those in normal type are typical properties.

Strength at Elevated Temperatures

On short term testing the properties fall slowly and uniformly up to 200°C. For prolonged heating above 135°C, the properties will be reduced by half.

Physical Properties

Coefficient of Thermal Expansion (per°C at 20-100°C) 0.000021
Thermal Conductivity (cal/cm 2 /cm/°C at 25°C) 38
Electrical Conductivity (% copper standard at 20°C) -
Density (g/cm 3 ) 2.68
Freezing Range (°C) approx 620-550


The heat-treated alloy has fairly good machining properties, but tools should preferably be of high speed steel, and must be kept sharp. A moderately high rate of tool wear may be expected. Liberal cutting lubricant should be employed. 

Corrosion Resistance

Resistance to corrosive attack by sea water and marine atmospheres is high. 


A protective anodic film can be obtained by either the sulphuric or chromic acid process but the grey opaque character of the coatings of normal thickness precludes their colouring in light shades for decorative purposes.

Casting Characteristics

  • FLUIDITY - Good, suitable for fairly thin castings.
  • TIGHTNESS - Good, suitable for castings required to be leak tight.
  • HOT-TEARING - Excellent. Problems due to hot tearing are seldom encountered.
  • The practical temperature may range between 675-790°C, depending on the mould configuration.
  • PATTERNMAKERS' SHRINKAGE - 1.3% or 1/75. 

Heat Treatment

L169 (solution heat treated and artificially aged) - heat at 535-545°C for not less than 10 hours, quench in water or in a polymer quenchant not hotter than 30°C. Artificially age at a temperature in the range of 155-165°C for not less than 2 hours, maintaining the selected temperature within a tolerance of +/-5°C, and air cool.

(The use of a polymer quenchant must be agreed with the purchaser.) 


L169 has high strength and toughness and is used in critical aerospace applications. It is easily weldable and may be heat treated. The permanent mould process is the preferred casting method for this alloy.