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ASTM A387 Grade 21 Steel vs. 7108 Aluminum

ASTM A387 grade 21 steel belongs to the iron alloys classification, while 7108 aluminum belongs to the aluminum alloys. There are 30 material properties with values for both materials. Properties with values for just one material (2, in this case) are not shown. Please note that the two materials have significantly dissimilar densities. This means that additional care is required when interpreting the data, because some material properties are based on units of mass, while others are based on units of area or volume.

For each property being compared, the top bar is ASTM A387 grade 21 steel and the bottom bar is 7108 aluminum.

Metric UnitsUS Customary Units

Mechanical Properties

Elastic (Young's, Tensile) Modulus, GPa 190
69
Elongation at Break, % 21
11
Fatigue Strength, MPa 160 to 250
120
Poisson's Ratio 0.29
0.33
Shear Modulus, GPa 74
26
Shear Strength, MPa 310 to 370
210
Tensile Strength: Ultimate (UTS), MPa 500 to 590
350
Tensile Strength: Yield (Proof), MPa 230 to 350
290

Thermal Properties

Latent Heat of Fusion, J/g 260
380
Maximum Temperature: Mechanical, °C 480
210
Melting Completion (Liquidus), °C 1470
630
Melting Onset (Solidus), °C 1430
530
Specific Heat Capacity, J/kg-K 470
880
Thermal Conductivity, W/m-K 41
150
Thermal Expansion, µm/m-K 13
24

Electrical Properties

Electrical Conductivity: Equal Volume, % IACS 7.6
39
Electrical Conductivity: Equal Weight (Specific), % IACS 8.8
120

Otherwise Unclassified Properties

Base Metal Price, % relative 4.1
9.5
Density, g/cm3 7.9
2.9
Embodied Carbon, kg CO2/kg material 1.8
8.3
Embodied Energy, MJ/kg 23
150
Embodied Water, L/kg 62
1150

Common Calculations

Resilience: Ultimate (Unit Rupture Work), MJ/m3 84 to 110
38
Resilience: Unit (Modulus of Resilience), kJ/m3 140 to 320
620
Stiffness to Weight: Axial, points 13
13
Stiffness to Weight: Bending, points 24
47
Strength to Weight: Axial, points 18 to 21
34
Strength to Weight: Bending, points 18 to 20
38
Thermal Diffusivity, mm2/s 11
59
Thermal Shock Resistance, points 14 to 17
16

Alloy Composition

Aluminum (Al), % 0
92.4 to 94.7
Carbon (C), % 0.050 to 0.15
0
Chromium (Cr), % 2.8 to 3.3
0
Copper (Cu), % 0
0 to 0.050
Iron (Fe), % 94.4 to 96
0 to 0.1
Magnesium (Mg), % 0
0.7 to 1.4
Manganese (Mn), % 0.3 to 0.6
0 to 0.050
Molybdenum (Mo), % 0.9 to 1.1
0
Phosphorus (P), % 0 to 0.025
0
Silicon (Si), % 0 to 0.5
0 to 0.1
Sulfur (S), % 0 to 0.025
0
Titanium (Ti), % 0
0 to 0.050
Zinc (Zn), % 0
4.5 to 5.5
Zirconium (Zr), % 0
0.12 to 0.25
Residuals, % 0
0 to 0.15