To join together the dissimilar metals of steel and aluminium, the simultaneous establishment of several different technologies was required such as technologies to prevent corrosion (electrical corrosion) and thermal deformation caused by the different expansion rates of steel and aluminum.
Honda newly developed three technologies that enabled adoption of aluminum for the outer door panel.
Technology to join dissimilar materials: Adoption of ‘3D Lock Seam’ structure, where the steel panel and aluminum panel are layered and hemmed together twice. [See figure above].
Technology to prevent electrical corrosion: Adoption of highly anti-corrosive steel for the inner panel and a new form that assures the complete filling of the gap with adhesive agent. [See figure below]
Technology to control thermal deformation: Adoption of adhesive agent with low elastic modulus and optimised position of the 3D Lock Seam.
The advantages of these new technologies include elimination of a spot welding process required to join conventional steel door panels. Moreover, these technologies do not require a dedicated process; as a result, existing production lines can accommodate these new technologies.
The new technology contributes to the improvement of fuel economy and dynamic performance of the vehicle by reducing door panel weight by approximately 17 percent compared to the conventional all-steel door panel. In addition, weight reduction at the outer side of the vehicle body enables to concentrate the point of gravity toward the centre of the vehicle, contributing to improved stability in vehicle maneuvering.
Honda has been making a number of efforts to further reduce vehicle weight. In 2012, with the North American version of the all-new 2013 Accord, Honda began mass-production of a front sub-frame featuring the steel-aluminium hybrid structure that was made possible by the Friction Stir Welding (FSW) technology.