Investigation of the Possibility for Compensating the HAZ Softening of AA7075-T6

Abstract

New generations of high strength aluminum alloys are increasingly used in automotive industry. AA7075 is one of the strongest aluminum alloys in industrial use today. The outstanding strength properties open the possibility to use this alloy in automotive industry as a possible alternative material for car body elements instead of steels. Growing industrial demand of aluminum alloys led to the development new technologies, processes. Solution heat treatment, forming, and in-die quenching is one such technology. In our research work the different parts of the heat affected zone of AA7075-T6 high strength aluminum were examined. The thermal cycle of the heat affected zone was tested at four different temperatures (280 °C, 380 °C, 440 °C, 550 °C) with the help of physical simulation. The aim was to define the softening tendency of the heat affected zone after gas tungsten arc welding. Two heat input values 100 J/mm and 200 J/mm were selected in order to simulate a low and a high heat input welding at the given sheet thickness and welding technology by the application of Rykalin 2D model. Then the most critical subzone was selected for the further investigations. Therefore, the 380 °C temperature was examined in case of five more technical processes, which based on the solution heat treatment, forming, and in-die quenching process. The properties of the investigated subzone were examined by optical microscope and hardness test.