Hochfeste Al-Mg2Si-Gusslegierungen

Translated title of the contribution: High strength Al-Mg2Si casting alloys

Georg Dambauer

Research output: ThesisDoctoral Thesis

Abstract

Aim of the present work is to optimize the mechanical properties of hypoeutectic alloys of the type Al-Mg2Si. At the beginning of the alloy development, two reference alloys, which have good potentials concerning the static mechanical properties, are defined. The first one is a wrought alloy with high ultimate strain (EN AW 6101), the second one is a casting alloy showing high strength (EN AC-AlSi7Mg0,6). The first step is the examination of the static mechanical properties of the reference alloys for different heat treatment parameters. A test alloy of Al-Mg2Si-type is defined, which mechanical properties lie between the two reference alloys. Based on this test alloy, Nickel and Cobalt are added to bond the iron in an Al9Co2-phase and to increase strength by formation of Al3Ni, which exhibits a dispersion hardening effect. The last step of the alloy development is the addition of silver, which forms metastabile semi-coherent Ag2Al-phases during heat treatment, which further increase strength and hardness. Subsequently two test alloys with different silver amounts are examined further. The static mechanical properties are investigated up to a temperature of 250°C. The results are compared to an EN AC-AlSi7Mg with and without an addition of 0,5 % Copper. In all cases, the silver containing alloys have better properties. The dynamic mechanical properties are examined under high cycle fatigue at temperatures up to 200°C with stress-Woehler-lines. The results are compared to a reference AlSi7Mg0,3Cu alloy. At room temperature, the reference alloy shows slightly better mechanical properties, while at 200°C the difference to the Ag containing alloys is more significant. Subsequently low cycle fatigue (LCF) for isothermal and thermo-mechanical fatigue (TMF) conditions are investigated. The LCF-tests are performed at room temperature and 200°C, the TMF-tests up to 250°C. For LCF-conditions, the test alloy is compareable with the AlSi7Mg0,3Cu alloy, under TMF-conditions, the gap between the test and the reference alloy grows bigger. To obtain improved results in TMF-tests, further investigations with small changes in chemical composition and heat treatment parameters should be conducted. The results of the casting technology trials are satisfying, obtaining a fine morphology and globulitic grain structure. However the alloy shows a tendency of hot cracking, which can be reduced by modifying the casting system. With some adaptions to the riser and gating system, engine and engineering parts are produced with good results regarding castability and performance. Phase simulations with Thermo-Calc and the investigation of physical properties complete the alloy examination in this work.
Translated title of the contributionHigh strength Al-Mg2Si casting alloys
Original languageGerman
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Schumacher, Peter, Assessor A (internal)
  • Antrekowitsch, Helmut, Assessor B (internal)
Publication statusPublished - 2010

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