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Ageing and cyclic stressing of 6xxx alloy core brazed sheet and its influence on the fatigue behavior
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2013 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

For heavy duty vehicles, radiators are typically made of aluminum brazing sheet with sometimes hardenable core. The 3 main components of a radiator are headers, tubes, and fins. At TitanX Engine Cooling, aluminum alloy 6xxx series have shown a good performance to produce radiators. Time and temperature, technological parameters, have strong influence on precipitation hardening and thereby mechanical properties of these alloys. 

In TitanX Engine Cooling, radiators undergo 14 days of Natural Ageing (NA) before set into service temperature of 95 ˚C. The aim of the study was to (1) shorten the 14 days NA while attaining the same mechanical properties and (2) evaluate the microstructure during simultaneous ageing and cyclic stressing. These were performed by means of mechanical tests (fatigue test, microhardness test, and tensile test) and advanced microscopy methods (Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), Electron Backscattered Diffraction (EBSD), Light Optical Microscopy (LOM) and fractography) on the header part of the radiator under different heat treatment conditions. 

Microstructure of FA7870 consists of primary particles, constituents, dispersoids and precipitates. The state of precipitation after 14 days NA is in co/clusters or/and Guiner- Preston zones. Analyzing the state of precipitation and dislocation-particle interaction for different heat treatment conditions (combination of both NA at room temperature and Artificial Ageing (AA) at 95˚C) with STEM did not provide any comparable results. This is due to the limitation of STEM to identify very small particles, GPZ. 

Based on the results obtained from mechanical tests, there is no correlation between static strength and dynamic strength. 6 days of NA+2days of AA at 95˚C provide the closest fatigue life to the reference heat treatment and is suggested to TitanX .

Place, publisher, year, edition, pages
2013. , 89 p.
Keyword [en]
Aluminium alloys, Fatigue, Heat treatment, Microstructure
National Category
Other Materials Engineering
URN: urn:nbn:se:kth:diva-122139OAI: diva2:620968
Educational program
Master of Science in Engineering - Materials Design and Engineering
2013-04-25, KTH, stockholm, 08:50 (English)
Available from: 2013-06-03 Created: 2013-05-13 Last updated: 2013-06-03Bibliographically approved

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