Influence of natural aging and repeated solid solution treatments on the microstructure and the mechanical properties of the alloys 7020 and 7175Thursday (09.11.2017) 10:55 - 11:15 Part of:
The 7xxx series (AL-Mg-Zn alloys) forms the group of the high strength aluminium alloys. Due to their high strength they are very interesting for the industry. However, the field of application is currently restricted due to their low ductility. Furthermore, during the storage at room temperature 7xxx alloys can age naturally by the precipitation of Guinier-Preston (I) zones, which are influencing the mechanical properties.
The aim of this study is to clarify how the natural aging and a repeated solid solution annealing are influencing the microstructure and the mechanical properties.
The alloys 7020 and 7175 were hot extruded and simultaneously solid solution annealed. After the extrusion process the alloys were analyzed in three different conditions: 1. after a subsequent peak aging, 2. after 18 month natural aging and subsequent peak aging, 3. after a repeated solid solution and subsequent peak aging. The microstructure was investigated using optical, scanning and transmission electron microscopy, the crystallographic texture by electron backscatter diffraction. The mechanical properties were investigated by tensile and compression tests.
The combination of extrusion processes and artificial aging leads to a significant increase in the elongation at fracture up to 16.7 % (increase of 20 %) in case of alloy 7020 and 14.5 % (increase of 30 %) in case of alloy 7175. Furthermore, it is shown that in case of the 7xxx alloys the natural aging does not lead to an embrittlement of the material after a subsequent artificial aging, which is a big advantage for industrial processing routes.