Experimental investigation of the damage characteristics of two cast aluminium alloys: Part I – Temperature dependent low cycle and thermomechanical fatigue behavior
Section snippets
Introduction and overview
Regarding the ecology of combustion engines, the present development and design is focused on the reduction of mileage and nitrogen oxides. The fuel efficiency is achieved by more efficient and highly loaded engines as well as by a lighter vehicle design. In many parts of combustion engines cast aluminium-silicon alloys are used, e.g. cylinder heads, pistons and engine blocks [1], [2]. The class of cast aluminium materials exhibits a high light weight potential due to its low density combined
Microstructure characterization and experimental details
In this chapter, the investigated materials and their specific microstructure are introduced in Section 2.1. The identification of the intermetallic phases is presented in Section 2.2. Further microstructural descriptors are determined in Section 2.3. Details of the test setup for the different experiment types are described in Section 2.4.
Basic material characterization
The cylinder head and piston cast aluminium alloys are characterized with regards to their temperature dependent fatigue properties. Tensile tests, isothermal complex low cycle fatigue (CLCF) and non-isothermal thermomechanical fatigue (TMF) tests were performed under strain control. The test results are used to calibrate and validate time and temperature dependent plasticity and lifetime models, which will be published in the future.
Temperature-dependence of isothermal Woehler curves
While the isothermal lifetimes in Fig. 13a of the cylinder head alloy AlSi7Cu0.5Mg-T7 alloy are hardly affected by the testing temperature for all investigated mechanical strain amplitudes, the isothermal lifetime behavior of the piston alloy AlSi12Cu3Ni2Mg-T7 in Fig. 13b is found to be strongly dependent on the temperature and the applied mechanical loading. Based on the observations above, it is assumed that the material’s specific microstructural behavior influences the mechanism of crack
Conclusions
In order to characterize the fatigue behavior of two cast aluminium alloys used for cylinder heads and pistons in combustion engines, tensile, low cycle and thermomechanical fatigue tests were performed over a wide temperature and loading range. The results are concluded as follows:
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Microstructural investigations using light microscopy and energy dispersive X-ray spectroscopy show, that the cylinder head alloy AlSi7Cu0.5Mg-T7 exhibits a finer microstructure in terms of silicon particle and pore
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors greatly acknowledge the financial support of the industrial collective research program (IGF No. 18921 N) supported by the Federal Ministry for Economic Affairs and Energy (BMWi) through the AiF (German Federation of Industrial Research Associations eV). Special thanks go to Karin Hintz for assisting during the EDX measurements and performing the metallographic and fractographic analyzes.
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