Aluminum, magnesium, and zinc are the most common alloys used in the die casting process. Aluminum and magnesium are considered to be relatively “lightweight” metals, and zinc alloys are a preferred metal to use in the miniature die casting processes and applications requiring thinner walls.
Deciding which alloy is best suited for a specific application of a die cast part is usually based on the design specifications – the alloy usually provides physical and mechanical properties that fit the end product application. It is important for a product designer seeking a die casting supplier to understand each type of alloy being offered and what benefits are involved.
Aluminum Die Casting Alloy
Aluminum is by far the most frequently used alloy in die casting. The most common aluminum die casting alloy is A380, which offers the best combination of material properties and castability. Aluminum alloy die castings are used in a wide variety of industries. It is common to see this alloy in electronics, communications equipment, automotive components, gear cases, lawn mower housings, hand and power tools, and many other products.
There are a number of aluminum alloys used in die casting. Each alloy has its own unique set of properties. Aluminum alloys for die casting have superior machining characteristics in comparison to iron, steel, and titanium. Amongst the other types of aluminum alloys, A380 has better than average machining characteristics.
Magnesium Die Casting Alloy
Magnesium alloys are the lightest of the commonly used structural metals used for die casting. Magnesium alloy AZ91D offers the highest strength of all commercial magnesium die casting alloys. It is also the most widely used. AZ91D Magnesium is a high purity die casting alloy which offers the following qualities:
– Excellent Corrosion Resistance
– Excellent Castability
– Excellent Strength
Corrosion resistance is achieved by enforcing strict limits on three metallic impurities: Iron, Nickel, and Copper.
Some of the more common applications for magnesium die castings are:
Automotive: cam covers, steering columns, steering wheels, brake and clutch pedals, clutch housings, seat frames, and dashboard supports; Portable tools such as: chain saws, drills, grinders, lawn mowers, string trimmers and pruners; portable electronics such as: projectors, cameras, radar indicators, calculators, and navigation devices; telecommunications equipment, levels; and recreational products such as: snowmobile components, archery bows, spotting scopes, etc.
While there are special precautions to take when machining or grinding magnesium die castings, magnesium alloys machine easily, requiring less power to machine than the other die casting alloys.
Finishing magnesium castings is similar to other alloys and any special treatments and coatings are usually taken into account when considering the end product and application.
Zinc and ZA Die Casting Alloys
Zinc and ZA alloys are commonly used for smaller die castings or die castings that require thinner sections. Zinc alloys generally allow greater variation in section thickness and can maintain closer tolerances. The impact strength of zinc die cast components are higher than the other common metal alloys, with the exception of brass. Also, because Zinc and ZA alloys require lower pressure and temperatures in comparison to magnesium and aluminum alloys, the die life is significantly longer and maintenance is relatively minimal.
Zamak alloys all contain approximately 4% aluminum and a smaller percentage of magnesium to make sure strength, hardness, and corrosion resistance properties can be achieved.
When it comes to miniature die castings, zinc is definitely the route to take. Miniature zinc die castings can be produced at high volume using special hot-chamber die casting machines that yield castings which are flash-free, with minimal draft and very close tolerances, requiring no secondary trimming or machining.
Zamak #3 is the most common of the Zinc alloys for die casting, offering the best combination of mechanical properties, castability, and economics. These zinc alloy metals have the ability to produce castings that have intricate details and surface finish at high production rates.
ZA alloys have more aluminum and copper content in them than the Zamak group for several reasons: higher strength, superior wear resistance, superior creep resistance, and lower densities. ZA-8 is the sole ZA alloy that can be die cast by the faster hot-chamber process.
Machining characteristics of Zamak and ZA are very good and both alloys have the ability to accommodate high-quality surface finishes when routine guidelines for machining zinc are followed.