Investigation Of Nugget Corrosion In Resistance Spot Welding

The phenomenon of metal corrosion has existed in various fields of national economy and defense construction. It has brought great loss. Now, many remarkable results on metal corrosion have been realized after some decades of years. However, with the rapid development of modern industry, the weld zones in metal components are more and more, so the corrosion of weld zone has become a hot issue. As an important branch of welding, resistance spot welding (RSW) has been applied in aerospace, automotive industries and other areas recently. The RSW process results in nugget, the corrosion behavior of which is different from base material. In this article, recent research development of corrosion behavior of weld is reviewed firstly, the influence factors are analyzed and the developing trend is prospected.The purpose of this paper is to study the corrosion behavior of 5052 aluminum alloy base metal and the nugget in 3.5% NaCl solution and water, and based on the theory of cellular automaton, the corrosion damage evolution process of nugget are simulated by Matlab, in order to make the corrosion process more intuitive.The main contents of this paper are as follow: firstly, nuggets of 5052 aluminum alloy and Q235 cold rolled steel were compared with base metal by analyzing the changes of open-circuit potential in 3.5% NaCl solution. Along with the corrosion morphology, the corresponding relation between microstructure and corrosion behavior is estimated. Secondly, the different corrosion behavior of nugget and base metal of 5052 aluminum alloy and Q235 cold rolled steel were investigated in order to assess the corrosive susceptibility with polarization under accelerated corrosion environment. Thirdly, the corrosion mechanism of nugget and base metal of 5052 aluminum alloy and Q235 cold rolled steel 5052 were studied with electrochemical impedance spectroscopy (EIS). Fourth, the simulation of nugget corrosion loss process is realized base on the cellular automata theory in Matlab language environment.Finally, the experimental and simulation results show: (1) The corrosion morphology of nugget and base metal of 5052 aluminum alloy and Q235 cold rolled steel belongs to pit corrosion, it is also found exfoliating corrosion; (2) For the nugget and base metal of 5052 aluminum alloy and Q235 cold rolled steel, the longitudinal section corrosive performance slightly is slightly better than the cross-section; (3) No matter what kind of materials the corrosive performance of nugget is slightly better than that of base metal; (4) The simulation results show that, with the increasing of time, the number of pitting is more and more, the size of pitting is bigger and bigger, but after a certain time the process of corrosion became more difficult, the rate of corrosion became more slow; at the same step of time, the concentration of electrolyte is bigger, the probability of dissolved is greater, the size of pitting is bigger and the situation of corrosion damage is more serious.