Corrosion Properties And Fatigue Properties Of 6005A-5083 Dissimilar Aluminum Alloy Welded Joints

Aluminum alloy has become the material of choice for manufacturing new highspeed train bodies due to its low density,high specific strength,and good formability.Aluminum alloy welded structural components are widely used in trains.Due to the significant differences in composition and organization in the joint area,they often become the weakest part of the joint,resulting in corrosion damage and fatigue damage in the process of use,which affects the safe operation of trains.Especially in the welded structure of dissimilar aluminum alloy,there are differences in alloy composition,grain size,and second-phase particle distribution in each region,resulting in dissimilar electrochemical properties,which increase the corrosion sensitivity of welded joints and make them susceptible to corrosion fatigue cracking under the coupling effect of cyclic loads.Dissimilar aluminum alloy welded joints are affected by different corrosive environments,the location of the occurrence of corrosion is still inconclusive,from the base material area to the weld core area there is the possibility of corrosion leading to fatigue failure,the internal causes still need further clarification.Therefore,this topic to 6005A-5083 dissimilar aluminum alloy welded joints for rail transportation as the object of study,its microstructural characteristics,mechanical properties,corrosion resistance,and fatigue properties of the systematic study,to explore the corrosion susceptibility of the joint,to reveal the joint fatigue performance degradation of the weak points and key factors,the topic can be used for rail transportation heterogeneous aluminum alloy welded joints of corrosion resistance and fatigue performance This project can provide theoretical and experimental support for the study of corrosion resistance and fatigue performance of heterogeneous aluminum alloy welded joints for rail transportation.The main conclusions are as follows:6005A-5083 joints in the welding process,the Mg element in weld zone to6005 A heat-affected zone(6005A-HAZ)diffusion,the solid solution strengthening of Mg in the region,while the influence of welding heat,6005A-HAZ internal uniform distribution of β" phase coarsening,in the combined effect of the above two factors,6005A-HAZ appear obvious the hardness of Softening zone,the lowest value of hardness 51 Hv.The average yield strength,tensile strength and elongation of 6005A-5083 welded joints were 149.8MPa,196.3MPa,and 5.1%,respectively.All tensile specimens fractured at the lowest value of hardness in 6005A-HAZ,indicating that the softening zone is the weak point for tensile fracture of welded joints.6005A-5083 welded joints in each region of the intergranular corrosion and exfoliation corrosion sensitivity from low to high were WZ<6005A-HAZ<6005ABM<5083-HAZ<5083-BM.Electrochemical analysis shows that the corrosion potential of different areas of the welded joint is different,and the electrical coupling effect occurs in the corrosive solution.The highest corrosion potential in the WZ(-1.088V)and the lowest in the 5083-BM(-1.322V),so that in the corrosion cell,5083-BM(anode)exhibits accelerated corrosion to protect the WZ(cathode).The slow strain rate tensile results of the welded joints showed that they were not stressed corrosion sensitive for 3.5 wt.% Na Cl solution,and the stress corrosion fracture location was also located in the 6005A-HAZ softening zone,and the fracture showed tensile fracture characteristics.The intergranular corrosion resistance of welded joints in three different salinity and acidity of corrosion solutions are different,intergranular corrosion crack expansion is more sensitive to HCl solution,and the depth of intergranular corrosion in the 5083-BM is the largest.Under corrosion-free conditions,the fatigue ultimate stress of 6005A-5083 welded joints is 96 MPa,and the defects in the weld joint area are the main factors for fatigue specimen cracking.When intergranular corrosion cracks exist in the joint,it is found that when the corrosion depth is <248μm,welding defects are still the dominant factor in determining the location of the fracture,fatigue performance degradation of the weak region for the WZ zone;and when the corrosion depth >248μm,intergranular corrosion cracks in the 5083-BM region will become the main crack of fatigue cracking,resulting in a change in the location of fatigue cracking.6005A-5083 welded joints of corrosion damage tolerance 248μm can be used as the basis for the assessment of the actual use of this joint in overhaul and maintenance.