Development of a laboratory-scale Upset Protrusion Joining (UPJ) system for dissimilar materials

Magnesium alloys have a significant benefit over steel and aluminum alloys in manufacturing components for many automotive and structural applications because of their higher light-weighting potential, lowest density, and higher strength to weight ratio. However, one of the impediments to the success of multi-material integration of the above materials for automotive manufacturing is joining these materials together without any cracking or corrosion during in-service use. The present work aims to develop and demonstrate a cost-effective, novel, and versatile mechanical joining technique, named Upset Protrusion Joining (UPJ), to mechanically and rapidly join a cast magnesium component to an aluminum alloy sheet. The process involves a cylindrical protrusion emanating perpendicular to the flat surface of a cast plate that fits through a hole in an aluminum sheet. The two components are then clamped together, electrically heated, and compressed perpendicular to the protrusion axis. During compression, the protrusion expands circumferentially to fill the hole as well as the region above the hole, thus entrapping the sheet metal between the mushroomed head and the casting. The effect of different UPJ process parameters such as applied current, current duration, compression loading rate, and compression distance were studied through experimentation on die-cast magnesium alloy, with protrusion of 11 mm diameter and 14 mm height. Material-specific process window was identified to achieve a satisfactory joint quality in terms of post-UPJ joint strength with appearance. UPJ method shows a great promise to implement in automotive and other industrial manufacturing environments for fastening cast components to a similar or dissimilar wrought sheet component.Graphical abstract