When brining a new product to market, it is important to select the right manufacturing process and the right material. Once a design engineer has identified that die-casting is the right process, there are several good casting materials to choose from. Zinc and aluminum are both common choices for die-casting. It’s important to consider the specific pros and cons of your product application when considering zinc alloy vs aluminum alloy. Although there is some overlap, often making the right material choice for the application will improve cost and performance.
This comparison examines zinc vs aluminum for die casting across tool life, costs, and performance. You will see which material fits your project best.
The material properties of the die cast metal you choose informs differences in application.
Zinc: low melting point, low abrasiveness, high fluidity, higher density
Aluminum: higher melting point, higher abrasiveness, lower fluidity, lower density
These few material properties impact almost all of the differences in the manufacturing use case of zinc vs aluminum, from tool life, to strength, to piece price, to tolerances, to secondary operations and more.
Die casting dies for zinc alloys last far longer than die cast aluminum tools. In general, a zinc mold can produce as many as ten times more shots than an aluminum casting die for the same part. For example, where a zinc tool may run 1,000,000 shots before the mold is worn beyond repair, an aluminum tool of the same part may only last 100,000 shots.
The molten zinc creates less stress on the mold and cavity thanks to a lower temp, lower abrasiveness, and higher fluidity. While there may not be an obvious difference on any given shot, these little differences accumulate to a much longer tooling life.
If a part has high-volume, the tooling expense will be much more painful for an aluminum casting compared to the same part in zinc. However, if the part is low volume, the customer may have a much less painful tooling burden as the tool may not need to be replaced for multiple years.
Zinc stands out with high-volume running parts. Long tool life cuts costs dramatically, and fast cycles add to the savings. Medium volumes work with either material. Make sure you compare your specific costs carefully. Taking into consideration both future tooling and part prices.
Aluminum die casting is more effective for low-volume components when annual usage is under 50,000 parts. At Deco, we expect zinc tools to last between 750,000 – 1,000,000 shots. However, we’ve seen several tools with simple geometry run several million shots without issue.
Zinc and aluminum are both commodities, and their prices fluctuate in real time based on trading on the London Metal Exchange (LME). There is no outright advantage to one or the other from a commodity market perspective, as prices will continue to move around as global supply and demand change day to day.
However, aluminum and zinc are both sold by weight. Aluminum is less than half the density of zinc. As such, it takes less “material” of aluminum to fill the same cavity as zinc alloy for the same casting. In general, this means that larger parts, or parts that have more weight sensitive applications will typically align better with aluminum than zinc due to the amount of material.
It is possible for zinc to compete with aluminum if the design can be altered. Zinc castings can be made with thinner walls, and can offer higher impact strength than aluminum. Anytime we help a customer convert an aluminum casting to a zinc casting, the first question we will ask is “can we alter the design”. These design alterations can help produce a product that has the same overall profile and performance, but less weight to help optimize the price point of the casting.
In addition to designing thinner walls to save money, zinc is also great for product applications that require thin walls thanks to its high fluidity. In some designs, we can cast walls under 0.030 inches thick. Aluminum is not as fluid as zinc and requires thicker walls to fill out the part.
The ability to cast thin walls is derived directly from zinc’s superior fluidity.
The ability to produce parts with thinner walls also promotes more design flexibility with zinc alloys. Design flexibility increases with zinc alloys. In addition to thin walls, zinc can also fill difficult features thanks to the high fluidity.
Thin walls, tough corners, and complex shapes work better in zinc because the material flows like water as the molten zinc flows into the part. Other intricate details, such as external threads, can also be designed into the casting, rather than planned as secondary operations.
Although both zinc castings and aluminum castings may require additional operations after being cast, zinc’s high fluidity allows for both more complex features and tighter tolerances. This may eliminate additional machining operations when the casting is designed in zinc rather than aluminum. Thus, although a given part may have a lower material cost if made in aluminum versus zinc, the secondary operations of the aluminum may quickly outpace the material savings
Die casting zinc tends to produce an excellent finish quality thanks to the fluidity. Molten zinc is able to rapidly fill the cavity and form a dense “skin” on the outside of the casting. This “skin” makes an excellent surface for painting or plating. The casting can also be left unprocessed thanks to its natural corrosion resistance.
If a product has a decorative or visible application, it is commonly the cast that the zinc product can be shipped with fewer finishing operations, such as polishing or buffing, thanks to its fluidity.
Zinc holds tight tolerances well. All castings will undergo what is referred to as “heat-shrink”. When a casting is freshly made, it is still quite hot despite being cooled to a solid form. As the excited molcules of the casting continue to cool and slow down, they push against each other with less energy. Thus, as heat continues to escape the casting, the part will slowly shrink into it’s ultimate long-term shape.
Thanks to the lower melting temp of zinc, there is less cooling and less heat-shrink compared to other casting metals, which require much hotter temperatures. The zinc alloys we work with only shrink around 0.6% percent while cooling. Less heat leads to less shrink, which allows for better accuracy, tighter tolerances, and better stability.
Both zinc and aluminum are both nearly 100% recyclable. The salvaged material performs identically to the raw materially, meaning there is not strength or performance loss by salvaging any of the process scrap or waste. This means that working with aluminum and zinc castings have virtually no waste, outside of the heat to remelt the material.
However, zinc’s lower melting point offers a significant energy advantage: you need much less heat to melt zinc alloy compared to aluminum. From a practical standpoint, the production costs of working with zinc can be lower, since there is less input required.
This also means a substantially smaller environmental impact to work with zinc materials versus aluminum materials. Converting aluminum castings to zinc can offer both improved energy savings and a smaller environmental impact.
Zinc forms a protective outer layer of zinc oxide naturally. This layer protects against corrosion. The material self-sustaining process handles many environments well.
Aluminum alloys resist corrosion in different conditions. Both materials work in various applications; it is best to match the material to your environment.
Both metals accept surface treatments, such as powder coating and plating, which work well and add extra protection.
For more details on zinc’s corrosion behavior, read our article: Does Zinc Rust? Is Zinc a Good Corrosion Resistant Metal?
Zinc and aluminum have very similar static strength profiles.
However, for applications that need to optimize static strength per unit weight, aluminum is the superior choice. Alternatively, if the need is to optimize impact strength per unit of weight, zinc is likely the optimal material.
This applications will also depend on how large the overall part is. For very large parts, aluminum’s advantage is even more pronounced, as it can add strength without adding substantial weight.
Our engineers are well-versed in the use-case of zinc and will always let you know if you should consider an alternate material for your use case. In general, we tend to recommend anyone with a part weigh of more than 8 pounds to go directly to aluminum. At Deco, we’ve run parts as large as 6 pounds, but we find the sweet spot is more around 2 pounds or less, depending on the product.
When considering material for manufacturing die casting parts, look at the complete picture when evaluating costs. Zinc and aluminum die casting both have clear use-cases when they are a superior economic and technical choice. There is also quite a bit of overlap between the two use-cases. We use the following as a general rule: