Study On Corrosion Behavior Of Steel-Aluminum Jointing Materials Of Vehicle In Typical Environments

In order to achieve the goal of saving energy and resources,the automotive industry can use the method of reducing the body quality to achieve the constraints of the cars' energy consumption.At present,(galvanized)IF steels are mainly utilized to support the non-load-bearing structure of the automotive body.For reflecting the weight-reduction effect,the aluminum alloys are gradually introduced into the automobile sheet production market to replace some conventional(galvanized)IF steels.Therefore,to accomplish the connection between(galvanized)IF steels and aluminum alloys,the existing connection methods are mechanical connection and traditional welding.Due to the complex environments in which the cars are driven,the corrosion resistance of the car body in these typical environments has become an issue to be explored.Regarding the corrosion performance of IF-steel materials and their joints for automobile bodies in typical environments,many researches were attached on the corrosion characteristics of hot-dip galvanized IF steel/6000 aluminum alloys welding system.A little recent research advance in corrosion characteristics of typical environments were found.This experiment uses open circuit voltage,electrochemical impedance spectroscopy,potentiodynamic polarization curve,Mott-Schottky and other electrochemical test methods,combined with field emission scanning electron microscopy,X-ray photoelectron spectroscopy,EDS,metallographic microscope and other detection and analysis techniques.Respectively,the corrosion characteristics of galvanized IF steel/EN 6061-T6 aluminum alloy joints in typical environment under the connection of tox punching connection,self-piercing rivet,and arc brazing were studied and their corrosion resistance was also evaluated.Conductive comparative analyses are applied to explore the corrosion differences of different connecting method.The experiment achieved the following results:In the typical environment,the corrosion forms of SPR riveted IF steel/EN 6061-T6 aluminum alloy and tox punching joint(galvanized)IF steel/EN 6061-T6 aluminum alloy are galvanic corrosion.In the galvanized IF steel/EN 6061-T6 aluminum alloy joint,the tox punching joint exhibits more severe electrochemical corrosion after stress deformation than the SPR rivet joint,and the potential difference of the deformed/undeformed joint promotes circuit closure.The formation of circuit corrosion currents results in severe contact corrosion effects.The strain conditions of the stress pool at the tox stamping joint,such as extrusion and stretching,affect the corrosion performance of the local area.Arc brazing(galvanized)IF steel/EN 6061-T6 aluminum alloy exhibits severe contact corrosion due to the apparently active electrochemical activity of the weld zone.The AC impedance of SPR riveted galvanized IF steel/EN 6061-T6 aluminum alloy is represented by resistance-capacitance characteristics.The corrosion kinetic curve indicates that all connected samples have the passivation process in the anode region,and the electrode process is controlled by at least two time-constants.Pitting corrosion of EN 6061-T6 aluminum alloy is caused by the close proximity of the heterogeneity potential difference and the pitting potential.It exhibits severe pitting and denudation in neutral and acidic accelerated corrosion environments,and it also shows intergranular corrosion under SEM.Obviously,the aluminum alloy in the IF steel/EN 6061-T6 aluminum alloy tox punching joint has the most severe pitting corrosion.Due to the higher electrochemical activity of the welding zone,arc brazing(galvanized)IF steel/EN 6061-T6 aluminum alloy will form a "small anode large cathode" in three typical environments,resulting in contact corrosion effects.It shows galvanic corrosion.Galvanized-IF steel/EN 6061-T6 aluminum alloy riveted by SPR mainly exhibits uniform corrosion.The presence of SPR rivet inhibits the ion exchange of small anode and large cathode,which weakens the contact corrosion effect and has higher anti-corrosion application value.Therefore,SPR riveting galvanized IF steel/EN 6061-T6 aluminum alloy is the best choice for automotive steel and aluminum connecting materials to meet the development of energy saving,anti-corrosion and environmental protection.