Friction spot extrusion brazing of copper to AISI 304 stainless steel with Zn interlayer: effect of shoulder surface modification

The friction spot extrusion brazing of Cu and AISI 304 stainless plates was carried out with a pure Zn interlayer medium to prevent Cu-Fe reaction by changing the tool shoulder surfaces from smooth to scrolled shoulder. The metallurgical and mechanical characterizations and fracture behaviors of the as-welded joints were studied. The change in tool shoulder surface had no significant effect on the chemical composition and the formation of interlocked or the plastically deformed material flow zone of the joint at an unchanged processing parameter setting. The kernel average misorientation fraction, high angle grain boundaries, and dislocation density are slightly higher at the stir zone of the smooth shoulder-produced welds owing to the higher heat input in the scroll shoulder-produced counterparts. The change of the tool from a smooth shoulder to a scroll shoulder tool produced a slightly more flash (non-uniform), increased peak temperature (409–459 °C), caused a rise in the average grains (6.58–7.73 µm) and promoted the fracture load (1359–2249 N) of the welds. Because there is no upper sheet bulging-induced interfacial gap at the brazed zone the tensile result of the scroll shoulder-produced joint has improved.