Role of the Microstructure on the Galvanic Cell Behavior in Iron/Copper Bimetallic Composites Based upon an Ancient Quranic Metal Matrix Composite (QMMC)

Abstract Bimetallic corrosion results in accelerated deterioration of the less noble metal due to the galvanic coupling. Electrochemical reactions between metals lead to one metal acting as an anode, corroding more rapidly, while the other acts as a cathode, experiencing reduced corrosion. This process impacts various industries, from defense structures to electronics. A bimetallic composite comprising iron rods and a copper matrix was prepared by casting. Most bimetallic corrosion studies have focused on the effects of environmental conditions and the cathode/anode area ratio on coating layers in bimetallic joints. However, the present work introduces an innovation by investigating the influence of the interfacial microstructure between the two metals, as determined by different casting parameters, on the bimetallic corrosion of iron/copper composites. The casting parameters subject to variation were the steel rod numbers and preheat temperatures, as well as the cast composite’s cooling conditions. The different bimetallic composites, inside the mold, were cooled at three different rates. The interfacial zone microstructure was investigated by scanning electron microscopy, and electrochemical methods were used to assess its impact on the corrosion process in a 3.5 wt.% stagnant solution at ambient temperature. The obtained results indicated that the width of the interference region in bimetallic systems is directly proportional to the corrosion rate, as influenced by the galvanic cell effect. Therefore, when the width of the interference region increased from 2.5 µm to 6.3 µm, the corrosion current density increased from 35 µA/cm 2 to 54 µA/cm 2 , respectively. Beyond the interference zone, the corrosion rate decreased, indicating a shift toward pure metal pitting corrosion behavior. Furthermore, it was found that both the cathode-to-anode area ratio and the grain size exhibit a direct proportional relationship with the corrosion rate. This directly improves the durability of components used in electrical connections, thermocouples, and military applications, where Cu–Fe systems are widely implemented.