Abstract
Time-temperature-precipitation (TTP) diagrams deliver important material data, such as temperature and time ranges critical for precipitation during the quenching step of the age hardening procedure. Although the quenching step is continuous, isothermal TTP diagrams are often applied. Together with a so-called Quench Factor Analysis, they can be used to describe very different cooling paths. Typically, these diagrams are constructed based on mechanical properties or microstructures after an interrupted quenching, i.e., ex situ analyses. In recent years, an in situ calorimetric method to record continuous cooling precipitation diagrams of aluminum alloys has been developed to the application level by our group. This method has now been transferred to isothermal experiments, in which the whole heat treatment cycle was performed in a differential scanning calorimeter. The Al-Mg-Si-wrought alloy 6005A was investigated. Solution annealing at 540 °C and overcritical quenching to several temperatures between 450 °C and 250 °C were followed by isothermal soaking. Based on the heat flow curves during isothermal soaking, TTP diagrams were determined. An appropriate evaluation method has been developed. It was found that three different precipitation reactions in characteristic temperature intervals exist. Some of the low temperature reactions are not accessible in continuous cooling experiments and require isothermal studies.
Highlights
The most important heat treatment to increase the strength of aluminum alloys is precipitation hardening, which is composed of three steps: solution annealing, quenching and ageing
All diagrams are scaled in the same way to enable the reader to see the differences in the signal intensity directly, which are dependent on temperature and time
The aim of this work was the development of a reliable method to record isothermal time-temperature-precipitation diagrams of aluminum alloys by in situ differential scanning calorimetry (DSC)
Summary
The most important heat treatment to increase the strength of aluminum alloys is precipitation hardening, which is composed of three steps: solution annealing, quenching and ageing. If quenching is too slow, coarse precipitates will form during cooling Those coarse precipitates do not increase the strength, but reduce the remaining solid solution available for the growth of strengthening precipitates during ageing. A broad range of isothermal time-temperature-transformation (TTT) diagrams and continuous TTT diagrams exist [1], because they can be determined by in situ dilatometric methods. For aluminum alloys, such time-temperature-precipitation (TTP) diagrams have been scarcely available in the past, due to the lack of suitable in situ characterization methods. A few isothermal TTP diagrams for aluminum alloys exist; these have been determined by ex situ characterization methods
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
