Joining magnesium and aluminum alloy sheets by a novel hole hemming process

Abstract

The use of magnesium alloys represents a novel trend in the automotive industry, being used to manufacture high performance vehicle structures. These alloys possess the lowest density among all structural metals. However, the use of joining processes based on plastic deformation of magnesium alloys is restricted by the low formability of these materials at room temperature. In this research work, a novel joining process, called hole hemming, is developed for attaching magnesium AZ31 and aluminum AA6082-T4 alloy sheets in which only one of the sheets should be sufficiently ductile and there is no need for heating or using additional elements, such as rivets. Firstly, the fracture limits of the materials were characterized under different loading states. Then, the process for joining the mentioned material combination was designed with the support of finite element analysis and the critical regions prone to fracture and their loading paths were specified. In addition, the influence of process parameters on the mechanical interlock was investigated to determine process windows. A flexible tool was then developed and, for the first time, novel hole-hemmed joints were manufactured with different process parameters to thoroughly evaluate the performance of the designed process. Finally, single-lap joints were tested under shear loads. The results of this tests show that the novel hole hemming process can suitably join the magnesium and aluminum alloy sheets, with the hole-hemmed joints supporting a maximum load of 2.9 kN with a gradual failure mechanism of hole bearing. Thus, the hole hemming process is shown to be a viable technique for joining materials with very different formability.