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Effects of Surface Roughness of Base Metals on the Residual Stress of Filler Metals at Brazed Joints

The purpose of this study is to make clear some effects of surface roughness of the base metals on the residual stress of the filler metals at brazed joints. Although brazing and soldering techniques have been used in the mechanical industry as the metallurgical joining process for a long time, both techniques are still extensively applied to assemble electric circuits, electronic instruments and other precision machine parts. This paper presents some experimental data of the relationship between the surface roughness of the base metals (mild steel, SUS410, pure Titanium and Ti-6A1-4V) and residual stress of the filler metals (Ag-Cu eutectic alloy, Pd-Ag alloy and Pd-Cu alloy) at brazed joints using 7kW resistance vacuum furnace. Through the study we arrived at the following conclusions: the residual stress at the brazed joints of the specimens with coarse surface of the base metals have a higher value than that of one with smooth surface of the base metals. In the process it's observed that the actual brazed area at the joint of the specimens with higher roughness has a higher stress value than that of one with smooth surface, that is, the shape factor value of the coarse roughness have the larger value than that of one with smooth surface of the brazed surface. And also, concerning the tensile strength of the brazed specimens, we have observed that the tensile strength of the brazed specimens with coarse surface have a higher value than that of one with smooth surface of the base metal. The above observation holds consistently for all the different materials used in this study.