When people ask if cast aluminum is stronger than aluminum, they are comparing two different classes of material produced from the same base metal. The term “aluminum” generally refers to wrought alloys, which are mechanically shaped into common forms like sheets, rods, or extrusions. Determining which material is inherently stronger is not a simple yes or no, as the superior choice depends entirely on the type of stress the material is expected to handle. A material’s performance balances properties like resistance to being pulled apart, the ability to bend without breaking, and hardness against surface wear.
The Difference in Manufacturing Processes
The fundamental distinction between cast and wrought aluminum begins with how the metal is processed from its initial molten state. Cast aluminum is created by pouring the liquid metal into a mold, where it cools and solidifies directly into the final shape, such as an engine block or a complex housing. While effective for creating intricate geometries, this cooling process tends to produce a coarser, more random internal grain structure that can include microscopic defects like porosity.
Wrought aluminum is mechanically worked while in a solid state using processes like rolling, forging, or extruding, rather than being poured into its final form. This intense mechanical deformation refines the grains into a fine, elongated, and aligned pattern. This directional grain structure eliminates many defects found in cast parts, fundamentally altering the material’s mechanical response to stress. The wrought process is ideal for creating standardized profiles, sheets, and structural components requiring high consistency.
Comparing Tensile Strength and Ductility
Wrought aluminum generally exhibits significantly higher tensile strength, which is the material’s resistance to being pulled apart before it fractures. A common wrought alloy like 6061-T6 has an ultimate tensile strength of around 310 megapascals (MPa), compared to roughly 290 MPa for a widely used cast alloy like A380. Crucially, the yield strength—the point at which the material permanently deforms—is much higher in wrought alloys (often 270 MPa) than in cast counterparts (which may only reach 160 MPa).
This difference in strength is closely tied to ductility, or the material’s ability to deform without breaking. Wrought aluminum is highly ductile, meaning it can bend and absorb energy under impact before failure, a property measured by elongation at break. For example, 6061-T6 aluminum can stretch by about 10% before fracturing. Cast aluminum, due to its coarse grain structure and internal imperfections, is typically more brittle, with alloys like A380 showing an elongation of only around 3.3%.
Although weaker in tension and more brittle, cast aluminum excels in other areas. Specific alloying elements, such as the high silicon content in A380, make cast aluminum effective at resisting wear and localized compression. Some cast alloys can also exhibit a higher fatigue strength than certain wrought alloys, allowing them to withstand more cycles of repeated stress before failing. This means cast aluminum’s strength favors resistance to surface stress over overall structural flexibility.
Where Each Material Excels
The differing mechanical properties dictate specific and optimal applications for each class of material, ensuring that the right type is chosen for the job. Cast aluminum is the preferred choice for parts requiring complex, three-dimensional geometry and high production volumes. Examples include automotive engine blocks, transmission housings, and intricate pump bodies. Its ability to fill complex molds easily, coupled with resistance to surface wear, makes it highly suitable for parts containing internal channels or complex mounting points. The cost-effectiveness of the casting process also allows for economical production of these detailed components.
Wrought aluminum is selected for applications where structural integrity, high impact resistance, and a high strength-to-weight ratio are paramount. This material is used extensively in aircraft frames, structural beams, vehicle chassis components, and bicycle frames. Its superior ductility allows it to absorb significant energy from sudden impacts without catastrophic failure, which is required for safety-related and dynamic load-bearing structures. Components needing precise dimensional control and a smooth surface finish also benefit from the uniform, fine grain structure of wrought alloys.