Analysis on Causes of Flaring Cracks in Thin-Walled 5A02 Aluminum Alloy Tubes

Abstract

In flaring process of some thin-walled 5A02 aluminum alloy tubes (“the tubes”) upon cold rolling and annealing, longitudinal cracks occur at the flared ends. In order to figure out the reason for these flaring cracks, observations and experiments are conducted on the cracks at flared ends by means of macroscopic examination, metallurgical microscope, scanning electron microscope, energy spectrometer and electronic universal testing machine. The experimental results show that for the tubes with flaring cracks, both the grain size and the difference among grain sizes are large. The distribution of second phase particles is nonuniform and aggregation of precipitation phase exist. The cracks nucleate and propagate under stress in regions where the inclusions are located. The defects, such as scratches and pitting, existing on the inner surface of the tubes, cause the nucleation and propagation of cracks in the defect regions under stress.