CREEP AND FATIGUE OF ZINC ALLOYS

Zinc alloys have reached a high level of usage today, often replacing aluminum due to their excellent strength, workability, and recyclability, making them a highly versatile material. Additionally, they are well-suited for processing via hot-chamber die-casting. As a result, zinc alloys are used in various sectors, from automotive to building products, constructions and electronics, meeting high performance standards both functionally and aesthetically. One disadvantage, due to their low melting point, is that zinc alloy components are susceptible to creep, a mechanism that could compromise the function of a component or lead to its failure. The primary objective of this work is to study the creep behavior of four zinc alloys produced via hot-chamber die-casting. Specifically, two well-known market alloys, Z410 and Z430, and two newly developed alloys, ZAMAK® Ultra, containing 50 ppm of titanium, and ZEP®1510, with a higher aluminum content than traditional ZAMAK alloys. Both new alloys were developed by Grillo-Werke AG and Didier Rollez, aiming to improve the mechanical properties of the alloy, particularly its creep resistance, thereby creating a product that fits better into the market and further increases the usage of zinc alloys made from hot-chamber die-casting. Metallographic analyses were performed using optical microscopy and SEM-EDS microscopy to study the microstructure and composition of the different phases. The microstructure, in addition to revealing the grain structure characterized by the high cooling rate in the surface layer, also allowed the identification of various morphologies of the alloys, with Z410 showing a more dendritic form compared to the others. The fine surface microstructure of the Z430 and ZAMAK Ultra alloys does not influence their respective creep behavior. Moreover, a high porosity was observed in the ZEP1510 alloy. SEM-EDS analysis indicated that titanium is homogeneously distributed across the different phases and increases the solubility of aluminum in both phases. The overall compositions of the various alloy phases were also determined. The creep phenomenon was studied by applying a constant load while maintaining the sample at a defined temperature. The tests were conducted under three different stresses (10 MPa, 30 MPa, 60 MPa) and at three different temperatures (60°C, 90°C, 120°C). The Z410 alloy exhibited good creep resistance under all conditions. ZAMAK Ultra performed well under extreme conditions, whereas ZEP1510 showed good creep resistance under mild stress conditions, although its behavior was unstable across various conditions. A secondary objective was to conduct some fatigue tests on the Z410 alloy using uniaxial dynamic tests with the "V2H 25 HCF" dynamic testing machine from DYNA-MESS GmbH, available at Aalen University's laboratory. These tests were carried out under stress control, at room temperature, with R = 0 and a frequency of 80 Hz. From these tests, a certain amount of specimen deformation was detected, so the objective became to study the simultaneous creep-fatigue behavior, attempting to correlate the results of creep and fatigue tests to identify any patterns. The results showed that frequency and stress do not influence elongation, but only the test duration changes. However, with a cycle ratio of R = -1, no deformation was observed. Creep tests conducted under the same temperature and stress conditions as the dynamic tests revealed that, at equal test durations, the deformation was 25 times lower in the creep tests compared to the dynamic tests. Therefore, it can be concluded that during dynamic tests, specimens undergo a certain amount of deformation, but this is not solely due to creep effects.