Electron beam welding of 7075 aluminum alloy: Microstructure and fracture properties

Abstract

Aluminum alloys have widespread use due to their superior properties. However, it exhibits complex effects with its various intermetallic compounds formed by clustering of other elements in its welded joints. In this study, electron beam welding (EBW) of the 7075 aluminum alloys (Al-alloys) was examined. Two different welding current values ​​are used in the welding process (20 and 25 mA). The welded specimens were subjected to tensile testing to determine their mechanical properties. In addition, the fractured surfaces were examined. The microhardness, scanning electron microscopy (SEM) and energy-dispersive spectroscopy analysis (EDS), EDS line analysis and EDS mapping were conducted. The microstructural evolution of EB welded plates investigated in the base metal (BM), heat affected zone (HAZ), and fusion zone (FZ), using SEM. Results indicated that after EBW, microhardness increment was observed in the FZ as compared to the BM and HAZ. The lowest hardness was observed in HAZ. The intermetallic formations in the FZ, and the effects of the elements on fracture were tried to be identified. At parameters 20 mA and 25 mA, 7075 alloys weld joints were brittlely broken. It was observed that the amount of Cu element increased at a high rate in the fracture zones of 7075 alloys (25 mA), it was clumped and active in fracture. Furthermore, it is estimated that a new formation is observed in the FZ of the welded joint made at 20 mA current in this study. As a result of the literature review, it is predicted that a natural structure similar to the one found in our study was not encountered for 7075 alloys or other welded Al-alloys. This formation was named, and the theory was put forward about the formation. The size, shape, chemistry and how this new formation came about were analysed.