Study On The Corrosion Behavior Of Friction Stir Welding Processed For Al/Cu Dissimilar Metals

The welding of dissimilar materials, like aluminum to copper, it is easily lead to hard and brittlesecond phase, thus affecting the mechanical properties of welded joints and service life. This articlemain studies on the corrosion behavior of welding joints who using friction stir welding ofaluminum/copper in different environments, hoping provide a theoretical basis for the application ofthe friction stir welding in aluminum to copper, and give relevant information for the optimization ofwelding process.In this paper, the corrosion behavior of5A06/T2welding joints is studied by immersion test,exfoliation corrosion test, intergranular corrosion test, acid salt spray test. The different regions of thewelded joints and macro-and micro-corrosion morphology was observed by using optical microscopeand scanning electronic microscope, and the electrochemical analysis on the different welding area isusing of the polarization curves and electrochemical impedance spectroscopy. There are severalresults as following.Large number of pitting corrosion appeared in the transition zone of the shaft shoulder whereclose to the copper matrix in the immersion test, preliminary line scan results show that the Mgelements segregated in this region, which is the main reason, induced pitting corrosion. The weld zonewas not sensitive with the intergranular corrosion test, the “tunnel type” was found in the junction ofaluminum and copper, it was due to aluminum/copper potential difference. Peeling corrosion wasfound in the weld joints, the pits were developing to the internal, and eventually lead to a largenumber of aluminum metal layers etched away, and form ravine morphology. The weld samples in theacidic salt spray were more serious corrosion, mainly concentrated in the central region,microstructure observed that corrosion developed to the material internal and were crack-like; weinferred that corrosion along the grain boundaries horizontal expansion, and with the tensile stress,intergranular corrosion developed into exfoliation corrosion. The shot peening does not improve thecorrosion resistance of the weld joints, and the mechanical properties of weld joints decreased rapidlywith the increase of corrosion time.Polarization curves showed that the aluminum thermo-mechanical affected zone and heataffected zone of the corrosion potential were the lowest, and the corrosion resistance are worse. Thenuclear area and aluminum parent material have the same equivalent circuit, the Nyquist plots in theheat-affected zone of copper side have the large capacitor curvature, and Impedance modulus was relatively large in the Bode chart, which showed that the thermo-mechanical affected zone of thecopper side had better corrosion resistance.