Construction of cooling rig and investigation of cooling sensitivity for aluminum crash alloy

Abstract: The work presented in this master thesis deal with the issue of quenching, investigation regarding different cooling rates and its effect on the material properties of aluminum alloy in the 6xxx series used for crash purposes in cars, such as crash boxes, beams and other crash relevant parts. Precipitation of Mg2Si due to different cooling rates affects the material properties such as crash performance, thus the aluminum alloy used is sensitive to different cooling rates. In order to perform tests with different cooling rates a cooling rig was constructed. In order to evaluate the different cooling rates both mechanical testing such as tensile test and 3-point bending test and compression test were performed. Also analyses with scanning electron microscope/energy-dispersive x-ray spectroscopy were performed to estimate grain boundary decoration of Mg2Si due to the different cooling rates. Furthermore LOM analyses were performed to evaluate if the experimental setup had any effect on material properties such as grain size. The constructed cooling rig produced different cooling rates with reliable repeatability as intended. Cooling rates between 130 ̊C/s and 20 ̊C/s were accomplished. Mg2Si occurred in all investigated test samples with various amounts. Higher cooling rates decreases the precipitation of Mg2Si to the grain boundaries, higher cooling rates also increased the bending angle achieved from the 3-point bending test. Furthermore, extensive solution heat treatment at elevated temperatures leads to grain growth.