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The influence of tensile pre-strain on the fatigue strength of asqueeze cast aluminum alloy cut out from a car wheel was investigatedunder rotating bending through the successive observations of the specimensurface by the plastic replication method. A crack was initiated from eithersurface slip bands or at an interface between eutectic Si particles and thematrix but was suppressed by eutectic Si particles in the materials withoutpre-strain.With tensile pre-strain, cracking or weakening occurred at aninterface between eutectic Si particles and the matrix, and consequently theinitiation of a fatigue crack was accelerated. However, the propagationprocess of a longer crack was suppressed by pre-strain.