Joining dissimilar grade aluminum alloy sheets using multi-hole dieless friction stir riveting process

Abstract

A recently developed spot joining process namely dieless friction stir riveting is explored for understanding the effect of multi-hole configurations on the joint formation in dissimilar grades of aluminum alloy sheets. These spot joints are strengthened by mechanical interlocking together with metallurgical bonding and possesses the absence of hook defect as well as pin hole defect. This contributes to superior lap shear fracture load than conventional spot joints. The mechanical load performance tests, detailed macro/micro structure analysis, the hardness measurement, external morphological study, and fracture mode analysis are conducted. Single-hole configuration yields appreciable mechanical performance than multi-hole configurations by achieving lap shear fracture load accounting about 7.42 kN and cross-tension fracture load accounting about 2.89 kN. The farther the holes in multi-hole configurations, the more imperfect the mechanical interlocking becomes. The dynamic recrystallization, associated grain growth, and its relation with the extent of plastic deformation in distinct zones of the joint are also identified. The frictional heat flux and severe plastic deformation have significantly affected the hardness of the two sheets. Critical weak zones leading to various fracture modes of the joint are also identified.