Aluminum castings are produced in a range of alloys demonstrating wide versatility in the characteristics than can be achieved. More than 100 compositions are registered with the Aluminum association, and more than 300 alloys are in international use. Properties displayed by these alloys, without considering the expanded capabilities of metal matrix and other composite structures, include:
Tensile strength, ksi (MPa) 10–72 (70–505)
Yield strength, ksi (MPa) 3–65 (20–455)
Elongation, % <1–30
Hardness, HB 30–150
Electrical conductivity, % IACS 18–60
Thermal conductivity, Btu · in./h · ft 2 ·°Fat77°F (W/m·Kat25°C) 660–1155 (85–175)
Fatigue limit, ksi (MPa) 8–21 (55–145)
Coefficient of linear thermal expansion at 68–212 °F (20–100 °C) 9.8–13.7 [1] 10–6/°F (17.6–24.7) [1] 10–6/°C)
Shear strength, ksi (MPa) 6–46 (42–325)
Modulus of elasticity, 106 psi (GPa) 9.5–11.2 (65–80)
Specific gravity 2.57–2.95
An ability to produce near-net-shape parts with dimensional accuracy, controlled surface finish, complex geometries including internal passages, and properties consistent with specified engineering requirements represents significant manufacturing advantages
- In many cases, multicomponent welded or joined assemblies can be replaced with a single cast part.
- Machining requirements are reduced.
- Aluminum castings display controlled variations in as-cast finish.
- Contrasts between as-cast and machined finishes can be highlighted to create pleasing cosmetic effects.
- Capital requirements are typically less than for wrought products.
- Tooling can range from simple patterns to complex tool steel dies depending on product requirements and production volume.
- Metallurgically or mechanically bonded bimetal parts can be routinely cast.
- Aluminum parts are routinely cast by every known process, offering a broad range of volume, productivity, quality, mechanization, and specialized capabilities.
- Most aluminum casting alloys display solidification characteristics compatible with foundry requirements for the production of quality parts.
- Many aluminum casting alloys display excellent fluidity for casting thin sections and fine detail.
- Aluminum casting alloys melt at relatively low temperatures.
- Aluminum casting processes can be highly automated.
Many limitations do apply. Very thin sections may not be castable. There are practical limitations in size for specific casting processes. The solidification behavior of some alloys precludes casting in difficult engineered configurations or in specific casting processes. The casting process is simpler and less capital intense than processes for producing forgings, extrusions, and rolled products.
However, solidification in complex geometrical shapes, as with other fabrication options, can result in surface discontinuities and internal microstructure features with varying degrees of quality that affect properties and performance.
Aluminum alloy castings can display the tensile properties of most forgings, extrusions, and rolled plate. Because wrought products are normally characterized by finely recrystallized grain structures with specific anisotropy and highly textured microstructural features, ductility in longitudinal directions is typically greater than in castings that contain coarser grain structures. Conversely, the typically uniaxial grain structure and absence of anisotropy in cast structures do not present design engineers with the challenges associated with transverse property limitations.
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