Corrosion Characteristics Of Welded Joints Of Body And Protection Measures In Marine Environment

With the progress of domestic manufacturing technology, the rapid development of automobile, locomotive, high-speed rail and other industries, the export volume of domestic cars and locomotives gradually increased. Export methods are mainly for shipping and air transport. In marine environment, steel structure parts prone to large area of rust, especially welded joint of welding parts, corrosion on mechanical properties, appearance, etc. Which have caused adverse effects. Therefore, the study about corrosion behavior of the vehicle body, especially the welded joint,and protection methods in the marine environment, which has important scientific and engineering applications value.To determine the effect of microstructure and morphology on the corrosion rate of welded joint, through the method of roughness and microstructure analysis. At the same time, to test corrosion rate of the sample which made from the different welding processes (CO2 gas shielded arc welding and SAW) and different position of welded joints (weld, heat affected zone and parent metal) through electrochemical method, discusses the reasons for different rate of corrosion, to obtain the corrosion law of two kinds of welding methods in 3.5% NaCl solution. Through Cyclic corrosion test to test corrosion corrosion of sample which made from different welding methods and different positions of welded joints and further validate the test results of electrochemical methods. Finally, through the natural environment exposure test and neutral salt spray test to test the protective effect of routine packaging protection, such as PE bag sealed packaging, VCI(volatile corrosion inhibitor) bag and a new kind of packaging protection, and observe the welding joint corrosion characteristics and rules. Results show that:1) The welded joint of Q235 steel is positive relative to parent material. The weld and heat affected zone have greater corrosion tendency relative to the parent material. Electrochemical tests showed that no matter two kinds of welding process, weld has the maximum corrosion current, followed by heat-affected zone (HAZ).2) After 30 days’salt spray test, in PE bags, welding seam and HAZ have emerged signs of corrosion, which is more serious than parent material; in VCI bags, there is no rust except a little corrosion on weld; Under the protection of new packaging technology (VCI and cold spraying zinc), there is no any sighs of corrosion.3) Conventional packaging protection method has a certain protective effect on the parent metal and can not play a very good protection. The new packaging technology (VCI and cold spraying zinc) combines the double advantages of VCI technology and cold spray zinc technology, which have good protective effect on weld, HAZ and parent material, and does not affect the subsequent coating and the welding technology. The combination can be effectively applied to the prevent the welding parts from corrosion which needs export through shipping.