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242.0 (CN42A, A02420) Cast Aluminum

242.0 aluminum is an aluminum alloy formulated for casting. 242.0 is the Aluminum Association (AA) designation for this material. A02420 is the UNS number. Additionally, the SAE designation is 39. Older literature may refer to this material as ASTM CN42A, but this is now discouraged.

The properties of 242.0 aluminum include five common variations. This page shows summary ranges across all of them. For more specific values, follow the links immediately below. The graph bars on the material properties cards further below compare 242.0 aluminum to: ANSI/AA cast aluminums (top), all aluminum alloys (middle), and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.

Mechanical Properties

Brinell Hardness

70 to 110

Elastic (Young's, Tensile) Modulus

73 GPa 11 x 106 psi

Elongation at Break

0.5 to 1.5 %

Fatigue Strength

55 to 110 MPa 8.0 to 16 x 103 psi

Poisson's Ratio

0.33

Shear Modulus

27 GPa 4.0 x 106 psi

Shear Strength

150 to 240 MPa 21 to 35 x 103 psi

Tensile Strength: Ultimate (UTS)

180 to 290 MPa 26 to 43 x 103 psi

Tensile Strength: Yield (Proof)

120 to 220 MPa 18 to 32 x 103 psi

Thermal Properties

Latent Heat of Fusion

390 J/g

Maximum Temperature: Mechanical

210 °C 400 °F

Melting Completion (Liquidus)

640 °C 1180 °F

Melting Onset (Solidus)

530 °C 990 °F

Solidification (Pattern Maker's) Shrinkage

1.3 %

Specific Heat Capacity

870 J/kg-K 0.21 BTU/lb-°F

Thermal Conductivity

130 to 170 W/m-K 77 to 97 BTU/h-ft-°F

Thermal Expansion

22 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

33 to 44 % IACS

Electrical Conductivity: Equal Weight (Specific)

96 to 130 % IACS

Otherwise Unclassified Properties

Base Metal Price

12 % relative

Calomel Potential

-650 mV

Density

3.1 g/cm3 190 lb/ft3

Embodied Carbon

8.3 kg CO2/kg material

Embodied Energy

150 MJ/kg 64 x 103 BTU/lb

Embodied Water

1130 L/kg 130 gal/lb

Common Calculations

Resilience: Ultimate (Unit Rupture Work)

1.3 to 3.4 MJ/m3

Resilience: Unit (Modulus of Resilience)

110 to 340 kJ/m3

Stiffness to Weight: Axial

13 points

Stiffness to Weight: Bending

45 points

Strength to Weight: Axial

16 to 26 points

Strength to Weight: Bending

23 to 32 points

Thermal Diffusivity

50 to 62 mm2/s

Thermal Shock Resistance

8.0 to 13 points

Alloy Composition

Among cast aluminum alloys, the composition of 242.0 aluminum is notable for including chromium (Cr) and containing a comparatively high amount of magnesium (Mg). Chromium is used to limit grain growth during hot working or heat treatment, which improves ductility and toughness. Chromium also reduces the alloy's susceptibility to stress corrosion cracking. If the alloy is anodized, the presence of chromium will tend to add a yellow tint to the film. Magnesium promotes hardenability through both heat treatment and strain hardening mechanisms. It also increases susceptibility to intergranular corrosion.

Aluminum (Al) 88.4 to 93.6
Copper (Cu) 3.5 to 4.5
Nickel (Ni) 1.7 to 2.3
Magnesium (Mg) 1.2 to 1.8
Iron (Fe) 0 to 1.0
Silicon (Si) 0 to 0.7
Manganese (Mn) 0 to 0.35
Zinc (Zn) 0 to 0.35
Chromium (Cr) 0 to 0.25
Titanium (Ti) 0 to 0.25
Residuals 0 to 0.15

All values are % weight. Ranges represent what is permitted under applicable standards.

Followup Questions

Similar Alloys

Further Reading

ASTM B618: Standard Specification for Aluminum-Alloy Investment Castings

ASTM B108: Standard Specification for Aluminum-Alloy Permanent Mold Castings

ASTM B26: Standard Specification for Aluminum-Alloy Sand Castings

Iron in Aluminium Alloys: Impurity and Alloying Element, N. A. Belov et al., 2002

Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, ASM Handbook vol. 2, ASM International, 1993