Die-cast zinc-based composite materials
Die-cast zinc-based composites use a zinc alloy matrix and incorporate reinforcements to create a novel structural material. These materials combine the high fluidity and low melting point of zinc alloy with the high strength of the reinforcements, resulting in widespread applications in electronics, toys, automotive parts, and other fields. The melting point of the zinc alloy matrix is only 380-420°C, significantly lower than the 660°C of aluminum alloy. This reduces energy consumption during the die-casting process and extends mold life. Furthermore, the fluidity of zinc alloy is 1.5-2 times that of aluminum alloy, enabling the molding of complex precision parts with walls as thin as 0.5mm. The introduction of reinforcements significantly enhances the material’s hardness and wear resistance. For example, a zinc-based composite material with 10% glass fiber achieves a Brinell hardness of 120HB, more than twice that of pure zinc alloy.
Material composition design is central to optimizing the performance of die-cast zinc-based composites. Common zinc alloy matrices include Zn-Al-Cu and Zn-Al-Mg. ZA27 alloy (27% Al, 2.5% Cu) is the preferred matrix for composites due to its high strength and toughness. The choice of reinforcement phase must balance compatibility with the matrix and cost. Currently, alumina particles, carbon fibers, and boron fibers are widely used. Research has shown that when alumina particle size is controlled between 5 and 20 μm and the volume fraction is 15%, the composite material can achieve a tensile strength of 350 MPa and an impact toughness above 30 J/cm², meeting structural strength requirements without excessively sacrificing the material’s plasticity.
Die-casting process parameters significantly influence the molding quality of zinc-based composites. Due to the low melting point of zinc alloys, the die-casting temperature is typically controlled at 420-480°C, more than 200°C lower than that of aluminum alloys. This reduces the risk of oxidation of the reinforcing phase at high temperatures. However, zinc alloys solidify rapidly, and improper control of the injection speed can easily lead to uneven distribution of the reinforcing phase. Modern die-casting technology effectively addresses this problem by adopting a two-stage process of low-speed filling and high-speed injection: the low-speed stage (0.5-1m/s) ensures smooth entry of the melt into the mold cavity, while the high-speed stage (3-5m/s) prevents sedimentation of the reinforcing phase. In addition, the mold temperature must be maintained at 150-200°C to prevent premature solidification of the melt and ensure the density of the casting.
In terms of expanding application areas, die-cast zinc-based composite materials demonstrate unique advantages. In the electronics industry, connector housings made of composite materials not only meet plug-in and unplug requirements through high dimensional precision, but also reduce signal interference by enhancing the electromagnetic shielding performance of the phase. In the automotive industry, composite door handle components are three times more corrosion-resistant than traditional zinc alloys and can adapt to long-term use in humid environments. It is worth noting that the density of zinc-based composite materials (6.0-6.5g/cm³) is higher than that of aluminum alloys, which limits their application in lightweighting areas. However, it makes them irreplaceable in parts that require a certain sense of weight (such as high-end musical instrument accessories). According to market research, in 2024, electronic components will account for 45% of the global zinc-based composite die-casting market, becoming the largest application area.
The development of die-cast zinc-based composite materials still faces some technical bottlenecks. The corrosion resistance of the zinc alloy matrix is poor, especially in high temperature and high humidity environments, where intergranular corrosion is prone to occur, and needs to be improved through surface treatment (such as electroplating and passivation); the interface bonding strength between the reinforcement phase and the matrix is insufficient, and it is easy to peel off when subjected to force, affecting the overall performance of the material. To address these problems, researchers can increase the interface bonding strength by more than 40% by coating the surface of the reinforcement phase with a metal coating (such as a nickel coating); and the application of new corrosion inhibitors can increase the salt spray resistance of the composite material from 200 hours to more than 500 hours. In the future, with breakthroughs in low-cost reinforcement phase preparation technology, zinc-based composite materials are expected to replace traditional metal materials in more fields and achieve a balance between performance and cost.
