Investigation of Surface Oxidation Behavior on High-Tensile Brass and its Effect on Hot Forging

CW722R and CW617N brasses are well known for their good formability at elevated temperatures; hence, both alloys find application in forging applications. In practice, it has been observed that CW722R alloy requires a slightly higher forging temperature than CW617N. Studies on other alloys have shown that the response to manufacturing is related to the characteristics of the oxide formed in the surface. However, no studies have been performed to show the effect of surface oxidation on brass during forging. Therefore, the surface oxidation behavior of a CW722R and CW617N alloy was investigated during manufacturing, and its effect on forging was explored. For this purpose, SEM–EDS analysis was performed on the surface of the samples in order to measure the depth of the oxide layer and identify the composition of the oxide. In addition, thermodynamic and Pilling–Bedworth ratio calculations were employed to determine the chemical composition of the oxide layers and explain their mechanical response. The results show that the oxide layer consists of Cu2O/ZnO/PbO with an average width of 0.81μm to 4.1μm according to SEM–EDS analysis and thermodynamic simulation. The Pilling–Bedworth ratio was assessed, showing that the oxide layer is cohesive and protects the surface from further oxidation. In addition, the oxide layer has lower thermal conductivity than the alloy; therefore, during hot forging, the lower thermal conductivity of oxide layer helps to maintain the temperature at higher degrees and thus reduces the forging load.