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.
| Al | 88.4 to 93.6 | |
| Cu | 3.5 to 4.5 | |
| Ni | 1.7 to 2.3 | |
| Mg | 1.2 to 1.8 | |
| Fe | 0 to 1.0 | |
| Si | 0 to 0.7 | |
| Mn | 0 to 0.35 | |
| Zn | 0 to 0.35 | |
| Cr | 0 to 0.25 | |
| Ti | 0 to 0.25 | |
| res. | 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