Corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding in alkaline solution

Abstract

This study was done to evaluate the nugget zone (NZ) corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding (FSLW) in a solution of 0.015 mol/L borax (pH 9.3). To this end, dissimilar copper/ brass plates were welded with two dissimilar heat inputs (low and high) during the welding procedure. The high and low heat inputs were conducted with 710 r/min, 16 mm/min and 450 r/min, 25 mm/min, respectively. Using open circuit potential (OCP) measurements, electrochemical impedance spectroscopy (EIS) and Tafel polarization tests, the electrochemical behavior of the specimens in borate buffer solution was assessed. With the help of scanning electron microscope (SEM), the morphology of welded specimen surfaces was examined after immersion in the test solution. According to the results, the NZ grain size and resistance improvement reduced due to the nugget zone corrosion with a decreased heat input. The results obtained from Tafel polarization and EIS indicated the improved corrosion behavior of the welded specimen NZ with a decrease in the heat input during the welding process unlike the copper and brass metals. Furthermore, an increased heat input during the welding process shows a reduction in the conditions for forming the passive films with higher protection behavior.

摘要

本研究旨在研究0.015 mol/L 硼砂溶液(pH 9.3)中铜/黄铜异种搅拌摩擦焊(FSLW)接头的点焊熔 核区(NZ)的腐蚀行为。在焊接过程中,采用高热和低热两种热输入异种焊接铜/黄铜板,高热和低热输 入分别为710 r/min,16 mm/min 和450 r/min,25 mm/min。通过开路电位(OCP)测量、电化学阻抗光 谱(EIS)和Tafel 极化实验对硼酸盐缓冲溶液中试样的电化学行为进行评估。用扫描电子显微镜对试样 表面形貌进行观察。结果表明,由于热输入量的减小导致的NZ 腐蚀,点焊熔核区的晶粒尺寸和电阻 升高的幅度降低。Tafel 极化实验和电化学阻抗光谱分析结果表明,与金属铜和黄铜不同的是,在焊接 过程中,NZ 试样的热输入的减少改善了腐蚀行为。此外,焊接过程中热输入的增加对形成具有较高 保护性能被动薄膜的条件不利。