Effect Of Corrosion Conditions On Mechanical Behavior Of 5083/6005A Welded Joint

5083/6005A aluminum alloy,with lightweight,good formability,good corrosion resistance and other advantages,has been widely used in the manufacture of high-speed train body structure,hanging pieces and other vital components.5083/6005A aluminum alloys are often connected by welding in these critical parts.In practical operation,the critical components of high-speed trains usually have to suffer cyclic loading such as stop and vibration,and withstand various corrosive environments such as humidity and salt fog.These aluminum alloy welds are prone to crack initiation and failure fracture under the combined action of long-term stress and corrosive medium.However,the effect of corrosion on mechanical properties of welded joints is not clear.In this paper,the effects of corrosion conditions on the mechanical behavior of 5083/6005A welded joint were studied.The results are as follows.（1）The influence degree of the three corrosion solutions on the tensile properties and fatigue properties of 5083/6005A welded joints is 3.5%NaCl+0.01mol/LNaHSO₃,3.5%NaCl and 0.6mol/L NaHSO₃in descending order.The corrosion products of 5083/6005A welded joint in 3.5%NaCl+0.01mol/L NaHSO₃and 3.5%NaCl solution are Al Cl₃,Al（OH）₃,and the corrosion products of 0.6mol/LNaHSO₃solution are Al₂（SO₄）₃and Al（OH）₃.（2）With the increase of corrosion time,concentration and stress,the mechanical properties of 5083/6005A welded joints decrease and the corrosion becomes more and more serious.After 3,7,15 and 30 days of corrosion in 3.5%NaCl+0.01 mol/L NaHSO₃solution,the mechanical properties of 5083/6005A welded joint decreased by 17.5%,20.6%,26.7%and 29.5%respectively,and the fatigue life decreased by 84.5%,90.7%,93.1%and 95.7%respectively.The elongation of 5083/6005A welded joints in 3.5%NaCl+0.01mol/L NaHSO₃solution after 3,7,15 and 30 days decreased by 25.5%,26.6%,28.9%and 31%respectively,and the fatigue life decreased by 93.8%,96.3%,98.2%,99.9%respectively.（3）With the increase of maximum stress(σ_max),the crack propagation zone of5083/6005A welded joint decreases gradually.After 30 days of corrosion and stress corrosion,the 5083/6005A welded joint has multiple crack sources and uneven fracture morphology.Stress corrosion has a significant effect on the crack initiation behavior of 5083/6005A welded joints.Most of 5083/6005A welded joints without stress corrosion fracture on the6005A side,while most of 5083 welded joints fracture on the 5083 side after stress corrosion.（4）In the process of no stress corrosion of 5083/6005A welded joint,aluminum alloy defects or the second to get along with formation of the oxide film under the action of corrosive medium,are destroyed in the first place.At this point,the aluminum substrate and the second phase particles exposure in solution to form primary battery,leading aluminum alloy pitting corrosion.Then,the second phase near the substrate with the increase of corrosion time undergoes further corrosion.When the aluminum alloy matrix around the second phase is completely corroded,the second phase falls off and eventually forms corrosion pits.（5）During the stress corrosion process of 5083/6005A welded joint,aluminum alloy cracks or the surface peels off in the second phase under the action of stress and corrosive medium,leading to the rupture of oxide film.At this time,aluminum matrix and second phase particles are exposed to the solution and gradually dissolve to produce hydrogen and H⁺,forming corrosion pits.As the corrosion continues,the solution in the corrosion pit is acidified locally,and finally hydrogen embrittlement and microcracks occur.