Cast aluminum alloy is an aluminum-based alloy blended with other elements (mainly silicon, copper, magnesium) to improve fluidity during casting, mechanical strength, and corrosion resistance. Unlike wrought aluminum, cast aluminum alloy is formulated specifically to optimize the casting process — particularly mold-filling ability and shrinkage during solidification.
How cast aluminum alloy differs from wrought aluminum
Pure aluminum has low mechanical strength and poor fluidity for filling complex mold cavities. As a result, aluminum used for casting is always alloyed with a significantly higher proportion of other elements than aluminum used for rolling or extrusion.
The most important difference lies in silicon content. Cast aluminum alloys typically contain fairly high silicon (commonly from 7% to over 12% depending on the grade), whereas wrought aluminum rarely contains silicon at this level because silicon reduces workability for rolling or drawing. Conversely, high silicon content is exactly what gives casting alloys good fluidity, effective mold filling, and reduced shrinkage during solidification.
Main alloying elements and the role of each
Silicon — improves fluidity
Silicon is the most important alloying element in most cast aluminum grades. It lowers the alloy’s melting point and significantly improves fluidity, helping molten metal fill thin-walled, complex geometry within the mold before solidifying. High silicon content also reduces shrinkage during solidification, limiting shrinkage porosity defects.
Copper — increases strength, trades off corrosion resistance
Copper increases the alloy’s mechanical strength and hardness, especially after heat treatment. However, high copper content reduces corrosion resistance, particularly in humid or salt-exposed environments. Alloys with higher copper content are therefore typically favored for applications needing higher mechanical strength rather than maximum corrosion resistance.
Magnesium — improves strength and corrosion resistance
Magnesium increases strength and hardness through a precipitation-hardening mechanism, while also offering better corrosion resistance than high-copper alloys. This is why Al-Si-Mg alloys are often chosen for outdoor applications or environments with moisture exposure.
Iron — reduces die soldering but affects ductility
Iron often appears as an impurity that can’t be entirely avoided in recycled cast aluminum alloy, but is also deliberately kept at a certain level because it helps reduce die soldering during pressure die-casting. However, excessive iron content forms brittle phases within the metal structure, reducing ductility and impact strength.
Zinc and manganese — supporting roles
Zinc typically appears in small amounts, affecting strength and heat-treatment response depending on the alloy system. Manganese helps offset some of iron’s negative effect on ductility, while also helping improve high-temperature strength in some specialized alloy systems.
Key mechanical-physical properties to consider when choosing a casting alloy
When selecting an alloy for a specific product, five properties should be weighed simultaneously, since improving one typically involves a trade-off in another.
Tensile strength and elongation determine load-bearing and deformation capacity before failure. Alloys with higher tensile strength typically have lower elongation, meaning they’re more brittle — this trade-off should be weighed based on whether the product experiences static loading or impact.
Fluidity determines the ability to fill thin, complex features — typically proportional to silicon content.
Corrosion resistance matters for products exposed to moisture, chemicals, or salt — typically inversely proportional to copper content.
Thermal and electrical conductivity matter for heat-dissipation or electrical applications — typically decreasing as overall alloying element content increases.
Post-casting machinability affects the speed and surface quality when finishing with CNC machining — some alloys tend to gum up tooling or wear cutting tools faster than others.
Common cast aluminum alloy grades
Cast aluminum alloys are classified under different naming systems depending on the region — the American system (A380, A360), the Japanese system under JIS standard (ADC12, ADC10, ADC6), and the European system. Since Daiwa operates to Japanese technical standards, JIS ADC designations are the most commonly used in actual production.
| Alloy grade | Notable characteristics | Common applications |
|---|---|---|
| ADC12 | Good castability, decent mechanical strength, reasonable cost — the most widely used grade | Engine housings, automotive/motorcycle components, general industrial equipment enclosures |
| ADC10 | Lower copper content than ADC12, balances strength and corrosion resistance | Components needing moderate strength combined with surface aesthetic requirements |
| ADC6 (Al-Mg system) | Outstanding corrosion resistance, good strength but harder to cast | Components exposed to moisture, outdoor applications |
| A380 (US system) | Similar characteristics to ADC12, common under North American standards | Automotive components, electronics under US customer standards |
Alloy grade selection shouldn’t rely on a single standout property, but should be weighed comprehensively against the product’s actual application requirements — including the operating environment and post-casting machining requirements.
Applications by industry based on alloy properties
In the automotive and motorcycle industry, grades such as ADC12 or A380 are typically favored for their good balance of mechanical strength, castability, and cost — suited to parts such as engine housings and moderate-load brackets.
In the electrical and electronics industry, especially products requiring heat dissipation, alloys with lower alloying-element content are typically favored to optimize thermal conductivity, even at some cost to mechanical strength.
In outdoor equipment or moisture-exposed applications, Al-Mg system alloys (such as ADC6) are typically chosen for their outstanding corrosion resistance, despite being harder to cast and requiring more specialized mold techniques and casting-machine parameters.
Frequently asked questions
Is ADC12 always the best choice for pressure die-casting?
ADC12 is the most common grade thanks to a good balance of properties and reasonable cost, but it isn’t the optimal choice for every application — particularly for products needing high corrosion resistance or good thermal conductivity.
Can the alloy grade be changed midway after the mold has already been made?
Technically yes, but casting-machine operating parameters (pouring temperature, pressure) need to be re-evaluated, since each alloy has different fluidity and shrinkage characteristics that can affect product quality if not adjusted properly.
Is recycled cast aluminum alloy lower quality than primary alloy?
Not necessarily, if the recycling process controls impurity content well (especially iron). However, recycled alloy typically has higher iron content due to mixed impurities from various scrap sources, and should be checked for composition before use in applications requiring high ductility.
Contact Daiwa for advice on choosing the right alloy
If you’re not sure which alloy grade suits your product’s mechanical-physical requirements and operating environment, Daiwa’s technical team can advise based on your drawing and the product’s actual operating conditions.