In order to study the formation cause of abnormal bright spots on the surface of 1420 Al-Li alloy bottom cover plate for aerospace applications,the abnormal traces were analyzed by means of microstructure analysis,fracture morphology observation,energy dispersion spectrum analysis,micro-hardness test and chemical composition analysis.The results show that the abnormal traces on the surface of the bottom cover plate are bright crystalline defects which penetrate through the whole plate.The microstructure and composition of the traces are abnormal.Considering the production process of the bottom cover plate,the bright crystalline defects are formed during the melting of 1420 aluminum-lithium alloy ingots,which are metallurgical defects.Due to the poor quality of the film layer in the defect section,the bright spots are formed during the process of phosphoric acid anodizing.