In situ SEM based fatigue crack propagation behavior of hybrid laser welded 7075-T6

The fatigue crack propagation behavior of welded 7075-T6 aluminium alloy was investigated by scanning electron microscope in-situ observation in room temperature. These results indicated that differences of fatigue crack propagation behavior among fusion zone, HAZ (heat affected zone) and base metal were attributed to microstructural feature. The crack propagated in fusion zone perpendicular to the stress axis; Zigzag crack propagation path was formed in HAZ; Many secondary cracks were observed at the surface of fusion zone and HAZ. "Single crack" mode was found in base metal. In addition, the Paris law of fusion zone, HAZ and base metal for welded 7075-T6 aluminium alloy was obtained by calculating through the lengths of fatigue crack and cycles.