Friction Stir.pdf

1. Introduction The use of zinc-coated steels for the automotive body construction has increased significantly in the last 2 decades to enhance the durability of vehicle structures. The automotive industries are currently working to develop lighter and more fuel- efficient vehicles. A significant proportion of this effort is currently being directed toward the substitution of aluminum for steel in the body structure. Aluminum is considerably lower in strength and stiffness than steel, and the design of the spaceframe coupled with the use of thicker material sections, successfully compensates for this1). Nevertheless, the replacement of material presents a vital challenge with respect to the methods of joining to be used for fabrication in volume production. Over the last decade, friction stir welding (FSW) has offered excellent welding quality to the joining of aluminum, magnesium2，3), titanium4), copper5), and Fe alloys6－8). Recently, some trials have been made to join the dissimilar materials, for examples dissimilar Al alloys9) and aluminum to steel joints10－13). However, most of the FSW efforts to date have not involved joining aluminum to zinc-coated steel. From an industrial point of view, there seems to be considerable interest in extending the process to this joint. Therefore, this research has been aimed at investigating the performance of aluminum-to-zinc coated steel (Al/Zn-coated steel) lap joint by friction stir welding and metallurgical factors controlling the performance. 2. Experimental Details The materials used were a plate of commercially pure aluminum A1100H24 2.0 mm thick and a plate of low carbon Zn- coated steel 1.0 mm thick. The steel had Zn coating of 10μm thickness. The chemical compositions of base metals are shown in Tables 1 and 2. The microstructures of the base metals are shown in Fig. 1. The aluminum base metal presented grains elongated in the rolling direction, and the steel base metal showed ferritic structure due to it