Konferenzbeiträge

Nowadays, the use of light alloys in automotive and aerospace industries is increased, due to the higher demand for weight reduction. Substitution of copper by aluminium is widely persuaded in order to save weight and material costs, for battery components and wire connectors. The decreasing in the energy requirements of the manufacturing processes is also desirable, as well as the stability of material cost on the market. Therefore, the development of joining technologies of aluminium and its alloys, with acceptable weld characteristics and minimal energy consumption is demanded [1-3]. Friction stir welding (FSW) is the technique which was developed at The Welding Institute (TWI) UK in 1991 [3-8]. It offers various advantages such as small or no distortion, high mechanical properties, low energy consumption, no consumable material or shielding gas are needed, it offers convenient microstructure and is especially well suited to the welding of aluminium alloys [7]. The basic concept is relatively simple. A rotating tool with a special designed pin and shoulder penetrates the upper side of the sheet in the overlapping area until a certain plunge depth is reached. The process lasts until the sheets are joined. Then the rotational tool retracts, and a keyhole is formed. The keyhole affects surface quality and mechanical properties of the joints, especially on thin aluminium sheets. In this paper, the convex pin-less tool is used to overcome this disadvantage. The aim of this study is to evaluate influence of rotational speed on the microstructure of four-layer lap-joint from ultrathin aluminium-magnesium sheets during friction stir spot welding (FSSW).