Effect of residual stress on fatigue crack growth behavior of 2024-T3
and 7075-T6 aluminum friction stir welded joint
Abstract
Since aluminum alloys have the low melting point and high thermal
conductivity, friction stir weld (FSW)has been successfully used in the
aerospace industry as an alternative to traditional welding methods. In
the service of FSWed structures, the residual stress and external load
would result in a secondary deformation and residual stress
redistribution. Therefore, it is necessary to investigate the effect of
residual stress on the FSWed fatigue responses. This paper studied the
fatigue crack growth behavior of 2024-T3 and 7075-T6 homogeneous and
dissimilar FSWed joints. The finite element model was built to calculate
the fatigue crack growth rate of FSWed specimen, and the results were
compared with the experiment results. It was demonstrated that residual
stress significantly affected on the fatigue crack growth rate. Tensile
residual stress promoted the crack growth, and it offset the decrease of
fatigue crack growth rate by grain refinement. The numerical results
also indicated that the longitudinal residual stress showed the greatest
effect on the crack deflection. Under the same welding speed, the
fatigue crack growth rate of 2024 increased with the increasing
rotational speed. For the same rotational speed, the fatigue crack
propagation rate of 7075 decreased with the increasing welding speed.