How to Choose an Aluminium Alloy for Die Casting

One of the most frequently asked questions we receive at Saige is, “what alloy should I use for my casting?” We love getting asked this question. The alloy utilized in your casting affects the final properties, function, and price of your casting as well as the life on your die-cast tool.  Below is a simple checklist to define the best alloy for your application.

Answer the following simple questions to narrow down your search:

• Will your casting experience wear from motion against another part?
• Will your casting experience temperatures in excess of 500F during use?
• Will your casting spend its life outside and be exposed to water and salt?
• Does your casting need to be pressure tight?
• Will your casting experience high loads and be expected to function as a structural component?
• Will your casting require heat treating?

If you answered “no” to all of these questions, then you should use an alloy in the 380 Family. 

383 alloy is ideal for several reasons.

• It produces a casting with very good mechanical properties that meet the requirement of most applications.
• It has the lowest price per Kg because its chemical composition is very common in the secondary aluminum to recycle stream.
• It is a very friendly alloy for the die caster as it fills cavities well, minimizes soldering, and can be held at lower temperatures than other alloys.

If you answered “yes” to any of the questions, then a more specialized alloy should be considered. We’ve broken down common applications and their ideal alloys:

If your casting will experience high temperatures and be used in a wear application, then B390 alloy is an excellent choice.  Components such as engine cylinders, pistons, pumps, pulleys, and brake systems are produced with B390.

B390 alloy is considered a Hypereutectic alloy because it has between 16-18% silicon.  Molten aluminum becomes saturated with silicon at 13%.  The excess silicon forms crystals in the metal structure that function as hard-bearing material for wear and strengthen the casting at high temperatures. 

B390 alloy is an excellent material in the correct application, but it has certain challenges.

B390 alloy is difficult to machine.  The primary silicon crystals will wear machining tools more quickly than a typical 380 family casting.  It is important that the die caster understand how to handle molten B390 alloy.  Improper melt treatment results in the Silicon crystals fusing together.  If the crystals grow in excess of 150 microns they can cause significant machining tool wear and can even cause stress risers in the casting.

B390 alloy is very aggressive on die-cast tooling as well.  The molten material must be held at temperatures in excess of 1300F.  The higher temperatures and free-floating silicon crystals cause significant wear to the die-cast tooling, cold chamber, and melting furnaces.  You can expect at least 20% less tool life using B390 than you would experience with 380 alloys.

Alloys for Corrosion Resistance

Will your casting spend its life outside and need to resist corrosion?

Copper is an aluminum die casting alloy that reduces corrosion resistance.  360 alloy with only .6% Copper is an excellent choice for castings with this requirement.   Marine components and pumps are frequently produced from 360 alloys for this reason.

Alloys for Pressure Tight Applications

413 alloy is the Al-Si eutectic alloy.  This means it solidifies over the narrowest range of any of the die casting alloys.  Aluminum castings solidification begins at the die surface and the process continues progressively inward towards the thermal center of the casting.  The solidification front produces a sound skin that is pressure-tight.  Since this alloy solidifies in such a tight range, the pressure-tight skin extends much deeper into the casting than other alloys.

A casting produced from the 380 families can also be pressure-tight if the casting is designed with this in mind and the skin is not removed by a secondary machining process.

Structural Alloys

New alloys have been developed which allow die castings to be used for structural parts.  Examples of structural parts are automotive body components such as shock mounts, door panels, and engine cradles.  Structural alloys are also frequently be found in frames for the marine industry and the off-road recreation industry.  Structural castings will experience high mechanical loads during use and can be welded or riveted during assembly.

Iron is a necessary impurity in aluminum die casting alloys as it prevents the aluminum from soldering to the die steel during the casting process.  Structural alloys replace iron with Manganese and Strontium to prevent soldering.  Removing the iron significantly increases the mechanical properties of the alloy, allowing it to be used in structural applications.

Alloys play a huge role in the overall cost and performance of your die-cast tool. We developed our checklist to assist you in choosing the right alloy.  However, it is important to speak with your die caster about your casting’s specific requirements In order to determine the best alloy for your application. Interested in discussing your latest die casting project? Contact us at harry@seipo.cn.