Study On Electrochemical Corrosion Of 6082 Aluminum Alloy Under Different Processes

6082 aluminium alloy is heat-treated strengthening alloy,which has medium strength,excellent weldability and corrosion resistance.It is widely used in transportation industry.However,under specific conditions?snow water containing NaCl snow melting agent?,6082aluminium alloy is prone to electrochemical corrosion,which brings hidden dangers to traffic safety.In this paper,6082 aluminium alloy was treated by different processes?shot peening and laser melting?.The potentiodynamic polarization curves of the treated samples were measured.The microstructures of the samples were observed by optical microscopy?OM?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and Electron backscattered diffraction?EBSD?.Energy dispersive spectrometer?EDS?and X-ray diffractometer?XRD?were used to analyze the elements qualitatively and quantitatively in the surface micro-area of the sample.The hardness of the aluminium alloy samples before and after treatment was tested by hardness tester.The results showed that in 1.5% NaCl corrosive medium,the corrosion began at the secondary phase?Mg₂Si phase,Si phase and AlMnFeSi phase?,and gradually developed from single pitting corrosion in micro-area to large-area intergranular corrosion,which ultimately led to the complete failure of aluminum alloy materials.The surface roughness,compressive stress and microhardness of 6082 aluminium alloy increased after shot peening treatment.The electrochemical test results showed that the passivation zone of the sample after shot peening was elongated,the dimension passivation current decreased,the corrosion current density also decreased greatly,the corrosion rate of the alloy material descended,and the corrosion resistance improved.After laser melting treatment of 6082 aluminum alloy,the size,shape and number of the secondary phase particles in the melted layer changed significantly,which showed that the second phase of Mg₂Si basically dissolved,and the second phase of Si concentrates at the grain boundary.The microstructures of the solidified layer showed obvious grain refinement,and the homogenization degree of the structure was deepened.The samples were divided into solidified zone,transition zone and matrix zone from the surface to the interior of the solidified layer.The melting surface was equiaxed crystals with small grain size and there was dendrite with large size in transition zone.With the increase of laser power,the melting depth and grain size in each region increased,but the hardness decreased gradually.The results of polarization curve test showed that the corrosion resistance of 6082 aluminum alloy was enhanced after laser melting treatment,and the corrosion current density decreased greatly in macroscopic and the maximum corrosion depth decreased in microscopic.Under the same experimental conditions,when the laser power was 2000 W and the scanning speed was 900 mm/min,the corrosion resistance of 6082aluminum alloy sample was the best.