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Abstract No.: |
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Scheduled at:
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Tuesday, May 21, 2019, Saal Brüssel 5:20 PM Properties of brazed joints 1
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Title: |
Corrosion fatigue performance of brazed 304L stainless steel joints
using gold based brazing alloys
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Authors: |
Anke Kalenborn* / Dortmund University of Technology, Germany Matthias Manka / TU Dortmund University, Dortmund Wolfgang Tillmann/ TU Dortmund University, Institute of Materials Engineering, Dortmund Frank Walther/ TU Dortmund University, Institute of Materials Engineering, Dortmund
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Abstract: |
Brazing is considered as an economic joining technology that is even applicable for non-weldable material combinations and therefore established in a wide range of industrial applications, such as automotive parts. During the operation of e.g. exhaust gas heat exchangers, the fatigue loading of brazed components is superimposed by corrosive attack due to aggressive exhaust gases. In the present study, the influence of corrosion on the microstructure and the depending mechanical properties under cyclic loading of austenitic stainless steel AISI 304L brazed at 1.050 °C with the gold based brazing alloy BAu-4 is investigated. The corrosion fatigue behavior was characterized in synthetic test condensates with a composition according to VDA test sheet 230-214, which is established for condensate corrosion in exhaust gas-carrying components. Brazed joints were cyclically tested in air as well as in corrosive environments using a corrosion cell. Therefore, stepwise load increase tests complemented with plastic strain, temperature, electrical, magnetic, and electrochemical measurements were applied to estimate the fatigue properties. The results have been validated with constant amplitude tests until 2E6 cycles. Corrosion- and deformation-induced microstructural changes of base materials and diffusion zones were evaluated using light and scanning electron microscopy. Brazed AISI304L/BAu-4 joints show fatigue properties, comparable to the base material, with a fatigue strength of 397 MPa. An evaluation method, developed for metastable austenitic steels, was successfully applied for the brazed specimens in order to estimate the fatigue strength with a deviation of 4%. In this context, the DIC system has proven to be appropriate to evaluate the strain distribution and to identify the local damage mechanisms of the thin brazing seam. A significant degradation of the fatigue performance due to the superimposed corrosion was determined and quantified for the investigated brazed joints.
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