Evolution of silicon particle damage on fatigue crack initiation and early propagation in an aluminum alloy

Low-cycle fatigue tests under both mechanical cyclic and thermal cyclic loadings were conducted to study the behavior of fatigue crack initiation and early propagation by means of metallographic and scanning electron microscopy(SEM).The damage mode of silicon particles has significant influence on crack behavior.Cracks are induced from fractured particles in mechanical fatigue or from debonded particles in thermal fatigue.Initiation of cracks by breaking through particles happens in particles with non-equiaxial particles,while initiation of cracks from debonded interfaces happens widely in clustered particles.For cracks induced by fracture particles,the subsequent coalescence of microcracks proceeds through the alternation of brittle fracture of particles.The sequent broken of particles takes the important part in the early propagation stage of fatigue crack.