Corrosion Behavior Of 2219 Aluminum Alloy Self-Reacting Friction Stir Welded Joint

Self-reacting friction stir welding is an important complimentary technique for friction stir welding,especially fit for the girth welding of the 2219 aluminum alloy aviation tank.However,the corrosion behavior and corrosion mechanism of the self-reacting friction stir welded joints are unclear.The application and popularization of this technology are restricted in a great extent.In this dissertation,the 2219 aluminum alloy self-reacting friction stir welded joint was studied.The electrochemical test?the neutral continuous salt spray corrosion test and immersion corrosion test were adopted to consider the corrosion behavior and evolution law of the joint.Finally,reveal the corrosion mechanism of2219 aluminum alloy self-reacting friction stir welded joint.The results indicate that in the 3.5%NaCl solution,the self-corrosion potential of the base metal is more negative than that of the weld zone,which is prone to corrosion;the dynamic potential polarization curve show the same trend,and the corrosion rate of the base metal is faster than the weld zone by analysised the corrosion current density.The localized electrochemical impedance spectroscopy shows that the impedance of the center of the weld nugget zone is the largest,and the impedance value decreases toward the base metal zone.The corrosion tendency of each zone of the joint is:base metal>heat affected zone>thermo-mechanically affect zone>weld nugget zone.Through neutral continuous salt spray corrosion test and immersion corrosion test,it is manifested that the weld nugget zone exhibited superior corrosion resistance,only mild pitting corrosion occurs,but the the base metal corroded most serious,from pitting corrosion to exfoliation corrosion.Corrosion behavior of base metal signified that the development of corrosion occurred with pitting and intergranular corrosion,and eventually expand to exfoliation corrosion.By dynamics analysis of the weight loss of the samples after salt spray corrosion,the weight loss per unit area and the corrosion rate trend as y=a·t~b within a certain corrosion time.A preliminary exploration of the corrosion mechanism of the 2219aluminum alloy self-reacting friction stir welded joints revealed that the second phase particles played an important role in the corrosion procedure and they were the initial corrosion position.In the corrosive medium,the Cl~-destroyed passive film and penetrated into the matrix,thus,pitting begins;there is a potential difference between the copper-rich second phase particles and the matrix,which constitutes an etching cell,and the surrounding matrix dissolves to cause intergranular corrosion,which aggravates the degree of pitting;Ultimately,multiple pitting pits merged and lead to exfoliate corrosion.