MIG welding tests were carried out on specimens with and without cortical layer at the end of the 6005 A railcar body,respectively.The influence of the cortical layer on welded joint crack was studied.The results showed that under the same stress level,the cortical layer significantly reduced the fatigue life of the specimen,leading to unqualified fatigue performance.The coarser the grain size of the base metal near the weld zone,the more obvious the melting of grain boundaries,and the greater the tendency to pro-duce liquefaction cracks in this region.The fatigue fracture of the welded specimen with the cortical layer was straight and rough,with recrystallized structure in the heat-affected zone of the base metal on both sides of the filled metal,and the recrystallization phenomenon on the fracture side was more significant and the grains were coarser.And the microstructure characterized were the presence of particle and oxide inclusions within the filled metal structure,and microcracks in the heat-affected zone near the welding line.
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