Cast aluminum is aluminum that has been melted and poured into a mold to create a specific shape. Unlike wrought aluminum, which is mechanically worked through rolling, forging, or extrusion, cast aluminum gets its final form directly from the cooling of liquid metal. This makes it one of the most versatile and cost-effective ways to produce complex metal parts, from engine blocks to patio furniture to cookware.
How Cast Aluminum Is Made
The basic idea is simple: heat aluminum (or more commonly, an aluminum alloy) until it melts, pour it into a mold, and let it solidify. But there are several distinct methods, each suited to different needs.
High pressure die casting is the most common process. Molten aluminum is forced under high pressure into a mold made from hardened tool steel, similar to how plastic injection molding works. This produces parts quickly and with good dimensional accuracy, making it the go-to method for mass production.
Low pressure die casting works in reverse, pushing molten aluminum upward into a mold using pressurized gas at around 10 psi. This is the standard process for aluminum road wheels, steering knuckles, and suspension components where structural integrity matters.
Gravity permanent mold casting relies on gravity alone to fill a reusable steel mold. When sand or salt cores are placed inside the mold to create hollow internal features, the process is called semi-permanent mold casting. Beyond these, there are also sand casting (using compacted sand molds that are broken apart after cooling), investment casting (for highly detailed parts), and lost foam casting, where a foam pattern is vaporized by the molten metal as it fills the mold.
What’s Actually in the Alloy
Pure aluminum is rarely cast on its own. Nearly all cast aluminum is an alloy, meaning other elements are mixed in to improve how it flows into molds and how the finished part performs. Silicon is the most important addition. It dramatically improves castability, which is why the most widely used cast aluminum alloys are aluminum-silicon blends.
The two workhorses of the industry are A356 (roughly 7% silicon with a small amount of magnesium) and A319 (about 6% silicon with 3% copper). A356 shows up in structural and aerospace parts. A319 is common in automotive engines. For non-structural items like housings and covers, A380 (8.5% silicon, 3.5% copper) is a standard choice. Copper additions boost strength but reduce corrosion resistance. Magnesium improves strength while keeping corrosion resistance intact.
Key Physical Properties
Cast aluminum is lightweight, with a density about one-third that of steel. Its melting behavior depends on the alloy, but common aluminum-silicon casting alloys begin melting around 577°C (1,071°F), well below steel’s melting point, which is one reason aluminum casting is relatively energy-efficient.
Thermal conductivity varies quite a bit by alloy. Pure aluminum conducts heat at 237 watts per meter-kelvin. Cast alloys are lower. A356, a popular structural alloy, conducts at about 151 W/m·K, while A380 drops to around 96 W/m·K. This still makes cast aluminum a strong heat conductor compared to most metals, which is why it’s widely used in engine components, heat sinks, and cookware.
How It Compares to Wrought Aluminum
The core tradeoff between cast and wrought aluminum comes down to shape complexity versus mechanical strength. Cast aluminum can be formed into virtually any geometry in a single step, while wrought aluminum must be machined, drilled, milled, or otherwise shaped after production. That gives cast aluminum a major advantage for parts with complex curves, internal channels, or unusual profiles.
Wrought aluminum wins on strength and consistency. The mechanical working process aligns the metal’s grain structure and eliminates most internal defects. Cast aluminum, by contrast, tends to contain small voids (porosity) created by trapped gas or shrinkage during cooling. These tiny internal pockets weaken the material. Larger pores near the surface are particularly problematic because they concentrate stress and can become starting points for cracks under repeated loading. This is why cast aluminum typically has lower tensile strength than wrought aluminum and is more prone to brittleness.
Cast aluminum is also cheaper per pound and better suited to high-volume production. Wrought aluminum can be produced as thin as foil, while cast aluminum parts are generally thicker and heavier.
Common Uses
The automotive industry is by far the largest consumer. Engine blocks, cylinder heads, transmission cases, wheels, and structural suspension parts are routinely cast in aluminum. The combination of light weight and the ability to form complex shapes in one step makes it ideal for reducing vehicle mass without sacrificing design flexibility.
Outside of cars, cast aluminum appears in outdoor furniture (valued for its corrosion resistance and durability), lighting fixtures, power tools, pump housings, and electronic enclosures. In the kitchen, cast aluminum cookware is popular because the material heats evenly and is much lighter than cast iron.
Aluminum Leaching in Cookware
One concern specific to cast aluminum cookware is whether aluminum leaches into food, particularly acidic foods like tomato sauce. It does. Lab testing using a 4% acetic acid solution (simulating mildly acidic cooking) found aluminum leaching ranging from 9 mg to 219 mg per serving, depending on the cookware sample. The World Health Organization’s tolerable daily intake for a 70 kg adult is about 20 mg per day, meaning some uncoated cookware can exceed that in a single serving.
The variation is large because it depends on the alloy, the cookware’s surface condition, and whether it has been anodized or coated. Hard-anodized cast aluminum cookware creates a protective oxide layer that dramatically reduces leaching. If you’re concerned, using coated or anodized cookware and avoiding prolonged cooking of acidic foods in bare aluminum are practical steps.
Recyclability
Cast aluminum is fully recyclable, and recycling it uses up to 95% less energy than producing new aluminum from ore. Because aluminum doesn’t degrade during recycling, scrap cast aluminum can be remelted and recast repeatedly without significant loss in quality. This makes cast aluminum one of the more sustainable metal choices for manufactured goods, and a significant portion of the cast aluminum produced today comes from recycled material.