Zinc Alloys - Standardized Quality from Primary and Secondary Raw Materials

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9/22/2022 Basic knowledge

Zinc Alloys - Standardized Quality from Primary and Secondary Raw Materials

Many products we encounter in our daily routine contain zinc. Products manufactured by the zinc die-casting process are frequently encountered, usually completely unknowingly. Today, components made of zinc die casting are high-tech products that are used for a wide range of applications and are used in many areas of daily life, in automotive engineering, for e-mobility, but also in mechanical engineering, electrical engineering and electronics, for SmartHome as well as in construction.

Examples for zinc die casting - gear shift and shower head Zinc die casting impresses through its economy, precise casting technology, and high-quality surface design

Due to the sustainable properties of zinc and the manufacturing process, zinc die casting continues to gain importance. Zinc die casting enables the implementation of complex geometries with thin wall thicknesses at high reproducibility in tight tolerances and with high strength values. Quality and quality monitoring are crucial in the process chain - from the standard-compliant zinc die casting alloy to the finished castings. High-quality zinc die casting products require continuous quality monitoring - from the alloy, through the zinc die casting process, surface treatment, to the finished product.

Zinc Die Casting Alloys

 The alloys ZP0400, ZP0410, ZP0430, which were developed using the zinc die casting process back in the early 1930s, have become particularly popular in practice. They form the basis for the development of further zinc die casting alloys, for special applications such as very thin-walled casting or for the optimization of special surface properties. The alloys are based on fine zinc with a purity of 99.995 percent zinc. Pure aluminum, copper and magnesium are further components that significantly influence the property profile of the alloys: Copper improves tensile strength and hardness, and magnesium prevents intergranular corrosion. Aluminum favors the workability of the zinc as well as the most important service properties, i.e. tensile strength, elongation at break and impact bending strength. At the same time, aluminum drastically reduces the reactivity of ferrous materials in contact with the liquid melt at temperatures below 450 degrees Celsius. As a result, all zinc-aluminum alloys can be processed in the fast and highly productive hot-chamber die casting process.

Most zinc die casting applications in Germany today are carried out in ZP0410. The second most commonly used alloy, ZP0430, has a higher tensile strength due to its higher copper content and is harder. It is used in many die casting applications with particular frictional stresses, but also in tool and die making. Alloy ZP0400 is characterized by good physical and mechanical properties. It is used mainly in English-speaking countries and is preferred where dimensional stability is important. Alloy ZP 0810 is the alternative to ZP0430 and is also frequently used in the English-speaking world, with mechanical properties comparable to those of alloy ZP0430.

Properties of zinc die casting

  • Short casting cycle times due to low melting temperature (380-390°C)
  • Long die service life 
  • High economic efficiency
  • Excellent flow behavior (thin-wall casting)
  • Tightest casting tolerances
  • Good mechanical material properties (for ZP0410 e.g. tensile strength 330 MPa, yield strength (0.2%) 295 MPa, modulus of elasticity 84 GPa
  • Excellent conditions for surface finishing
  • Lowest lift-off chamfers; near-net-shape production
  • Electromagnetic shielding
  • Low energy consumption due to comparatively low melting temperature
  • 100 % recyclability
  • Circular economy potential End-of-life (collection, sorting, recycling)
Examples for zinc die casting in daily life Zinc die casting in everyday life - stable, top design, functional, sustainable

 

Standards

With the introduction of the European standards EN 1774 (zinc alloys) and EN 12844 (zinc die castings), the different European designations of zinc alloys and their chemical compositions have been harmonized: "It goes without saying that a zinc die casting alloy must comply with a standard, because the manufacturer must prove that this ensures optimum zinc die casting. The casting process must also be optimized to the highest standards in order to prevent changes in the alloy composition during the melting and casting process. Didier Rollez, Sales and Technical Consulting, Grillo-Werke AG, comments: "The criteria of EN 12844 give zinc die casting customers the necessary assurance that castings reliably and reproducibly meet the desired properties and can withstand the stresses during use over a long period of service."

 
Table of specifications for zinc die casting components Table 1: Specification of zinc die casting components according to EN 12844 EN 1774 for zinc die casting alloys (weight in %)

Quality Assurance

The basis of quality assurance is compliance with the required EN 1774 and EN 12884 standards: If, for example, the specified tolerance values for aluminum, copper and magnesium are undershot or overshot, this affects the mechanical properties and thus the functionality of the castings. Even very small amounts of lead, cadmium and tin - they often occur together in the ores and are separated during zinc extraction - lead to intergranular corrosion or grain boundary corrosion. As a result, quality problems can already occur during refining and castings can no longer withstand mechanical stresses after only a short time. Minor elements such as nickel, iron and silicon are also undesirable because they cause surface and finishing problems. Due to the increased requirements for closing material cycles (circular economy), alloys for zinc die casting are increasingly being produced from recycled raw materials. These processes require special attention to the alloy tolerances, because the recycled raw material already has a certain basic material composition/alloy from its initial use phase and must be adapted to the recipe of the zinc die casting alloys in the manufacturing process. To ensure alloy compositions that conform to standards, manufacturers rely on transparent quality management and high standards. During production, material samples are tested at several process steps by means of spectral analysis. The required alloying metals aluminum, copper and magnesium are matched to the desired alloy type. Clear product identification of the finished alloy ingots ensures complete traceability of the customer-specific batches. In this way, the requirements of standardization, as well as customer requests for alloys that are reproduced within low tolerance values are met.

Innovations

Starting from the proven zinc die casting alloys, there are continuous further developments of the alloys and the casting process. Reducing the weight of castings while maintaining the desired strength and shape is of particular interest for many applications. The following criteria are taken into account:

  • Lightweighting - reduction of the unit weight while maintaining the same strength. For this purpose, zinc foam is also used inside the casting, for example. A weight saving of up to 50% can be achieved here. The outer surface of the castings is closed and of high quality and optimized for subsequent surface treatment.
  • Resource conservation through thin walls - with a view to sustainability and with the aid of FEM simulation, castings are optimized in terms of design so that they can be implemented with low resource input, which in turn has a positive effect on cost efficiency. By adapting the alloy composition, among other things by using grain-reducing elements, the flow and mold filling properties have been optimized in such a way that the highest quality requirements can be realized, particularly for very thin-walled components (down to 0.3 mm) or high surface demands.

Outlook

Zinc die casting is widely used, for example, in automotive construction/mobility, mechanical engineering, furniture and fittings. For applications in the field of security and locking technology, zinc die casting scores points thanks to its good mechanical properties. The fact that zinc die casting is also capable of meeting new requirements is demonstrated by recent innovations focusing on constructive lightweight design, where the main emphasis is on weight reduction while retaining surface properties and mechanical properties. However, reliable and reproducible quality can only be achieved if the material quality and the quality in the casting process are coordinated and given top priority. In addition to operational measures, compliance with European standards for both zinc die casting alloys and zinc die casting parts is decisive in this respect.

 
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Authors

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Frank Neumann

Initiative ZINK Management

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Didier Rollez

Grillo-Werke AG