The effect of arc brazing process parameters on the microstructure and mechanical properties of high-strength steel HCT780XD using the copper-based filler metal CuAl8

The effect of undermatching, describing the joining of high-strength base materials with the use of lower strength filler materials, is one of the major common concerns resulting in the limited industrial application of arc brazing. A missing database of mechanical properties and in particular reachable joint strengths is a reason for not adopting the process in production. For this purpose, arc brazed joints of the high-strength steel, HCT780XD, with the copper-based filler-metal, CuAl8, were investigated. The objective of this work was to analyze quantitatively the influence of the CMT-SynchroPulse process and of the resulting intermetallic phase Fe3AlyCuz on the microstructure and mechanical properties of an overlap joint. Tensile strength tests and fatigue strength tests were conducted as well as metallurgical analyzation. The results showed that current industrial concerns about undermatching were not confirmed. For the CMT-SynchroPulse process and a defined amount of intermetallic phases a positive influence on the tensile strength could be determined. For an amount of approximately 8.5% of intermetallic phase within the brazing seam, samples failure occurred in the heat-affected zone of the base material. During the cyclic tests, a negative influence of a predefined gap between the lower and the upper sheet on the fatigue strength could be identified.