One of the strengths of die casting is the ability to leverage a variety of alloys in the process according to the needs of the part.
HERE, WE’LL DISCUSS THE ADVANTAGES AND DISADVANTAGES OF THREE COMMON GROUPS OF ALLOYS: ALUMINIUM, MAGNESIUM, AND ZINC.
You’ll see that no matter what you’re looking for, there’s very often a good die casting choice to be made!
Aluminum Alloys (Al)
With a specific gravity of approximately 2.7g/cc, aluminum alloys are amongst the lightweight structural metals. It’s also often the most economical die casting metal. In fact, the majority of castings, worldwide, are aluminum alloys.
Aluminum alloys typically involve six other elements: silicon, copper, magnesium, iron, manganese, and zinc. Each affects the metal independently and interactively.
Common Aluminum Die Casting Alloys
Alloy A380 – This is the most commonly used aluminum alloy. It has the best combination of material properties balanced with ease of production. You’ll see it used in electronic and communications equipment, automotive components, engine brackets, transmission and gear cases, appliances, lawn mower housing, power tools, and so on.
Alloy A383 – This is an alternative to A380 for more intricate components that need improved die filling characteristics or more strength at elevated temperatures.
Alloy A360 – When you’re looking for better corrosion resistance, higher strength at higher temperatures, and better ductility, you may turn to A360. The trade-off is it’s harder to cast and production yields decrease.
The machining characteristics of aluminum vary alloy to alloy — A380 has the best machining characteristics of the lot — but they’re all superior to iron, steel, and titanium.
Various surface treatments can be performed too, to protect the surface from exposures to environments, to add a decorative finish, and to increase resistance to wear.
- Powder coat
Protection from Environmental Corrosion
- Iridite coating
For improved wear resistance, hard anodizing can be applied to the part.
Magnesium Alloys (Mg)
Magnesium, with its specific gravity 1.74g/cc, is the lightest commonly used structural metal. The most used magnesium alloy for die castings is AZ91D.
This alloy offers the highest strength commercial magnesium die casting allows and has excellent castability and corrosion resistance too. This powerful corrosion resistance is achieved by imposing strict limits on the allowable impurities of three metals: iron, copper, and nickel.
Where will you find magnesium die cast parts? Steering columns, vacuum cleaners, cameras, sports equipment, sewing machines, and more.
MAGNESIUM IN THE DIE CASTING PROCESS
While magnesium is a solid choice for many die casting applications, it’s worth noting that it can be a dangerous element if it catches fire, or you’re working with molten magnesium.
Magnesium fires are incredibly dangerous because of the enormous temperatures involved — a magnesium fire can reach 3,100°C, with water only accelerating the fire.
Your parts will be fine. However, because of the danger, while magnesium has the best machinability of all commercially used metal alloys, special precautions must be taken when machining or grinding it.
For surface treatments, magnesium alloys can receive decorative chromate treatment, painting, plating, and phosphate coatings. Magnesium underbody auto parts do not use any special coatings or protections even though they are exposed to extremely harsh environmental conditions.
Magnesium used in computer parts will use chemical treatments to protect against tarnishing or slight surface corrosion. Painting and anodizing may also be used to protect against corrosion. Hard anodizing and hard chrome plating can further improve the wear resistance of magnesium.
ZINC ALLOYS (ZN)
Zinc alloys have the broadest of physical and mechanical properties — and have great castability and finishing characteristics.
You’re also able to get thinner sections than any other commonly used alloy.
- Generally allows for greater variation in section design
- Maintains dimensional tolerances better
- Higher impact strength than other common die cast alloys, with exception of brass
- Zinc is cast as much lower temperatures so die life is significantly longer and maintenance is minimized
COMMON ZINC DIE CASTING ALLOYS
Zinc Alloys include Zamak (acronym for Zinc, Aluminum, Magnesium, and Copper). The common ones are Zamak Series No. 2, 3, 5 and 7.
You’ll also see the high aluminum content group: ZA-8 through ZA-27.
Zamak contains nominally 4% aluminum and small amounts of magnesium to improve hardness and strength and to protect castings from corrosion. Zamak alloys all use the hot chamber process which allows for maximum casting speed.
Zinc 3 has the best combination of mechanical properties, castability and material cost and is the most used in North America. Other Zamak alloys are more expensive and typically reserved for rare occasions when specific properties are needed.
The ZA Series contain more aluminum than the Zamak group. The numerical number next to the ZA actually represents its aluminum content in %: ZA-12 is 12% aluminum, for instance.
The higher aluminum and copper in the ZA series gives some advantages over the Zamak series.
- Higher strength
- Better resistance to wear
- Creep resistance
- Lower densities
Zamak and ZA alloys lend themselves well to machining because high quality surface finishes can be achieved.
Zinc is used without surface treatment for many different applications, but painting, phosphate coating, chrome plating, and chromating can all be used for a decorative finish.
Painting, chromating, anodizing and iridite coatings are used as corrosion barriers. Hard chrome plating used for wear resistance — except for ZA-27.
Bright chrome plating of Zamak and ZA alloys make then a frequent choice for hardware applications.
DIE CASTING WITH SIMALEX
We’ve been in the die casting business for almost 60 years — and we know a thing or two about all these alloys. Whatever you’re looking to produce, we can take your specifications and requirements and make reliable, consistent recommendations about what your options are and which to choose.
To get in touch, head over to our contact page and let’s start talking about what we can do to make your parts a reality.