Influence of process temperature on hardness of friction stir welded high strength aluminum alloys for aerospace applications

AbstractThe increasing application of innovative materials, such as high strength aluminum alloys, is challenging the manufacturing processes of the Aerospace and Aeronautics Industries. Despite this challenge the processes need to comply with high requirements regarding the reproducibility and the quality of the products. For this reason the adaption of conventional welding technologies to the new materials is considered to be difficult. Therefore, innovative welding technologies such as Friction Stir Welding (FSW) have been developed [1].This paper deals with the implementation of FSW into a new production process for lightweight dome structures of fuel tanks: Starting at temper condition O two AA 2219 plates are joined using FSW technology to form a larger blank. After that, the blanks are formed to shape using spinforming technology. The manufacturing process is accompanied by several steps of heat treatment to accomplish a finished tank-dome in temper condition T8.The studies presented in this paper aimed on finding a correlation between the process parameters and the properties of the welding seam, which are essential for the following spinforming process. For this purpose the experiments were conducted using design of experiments (DoE). The resulting hardness increase of the welding seam was chosen as target variable. Based on the acquired data a regression model was established and used to estimate optimal parameters for dome production

Formation of joining mechanisms in friction stir welded dissimilar Al-Ti lap joints

Friction Stir Welding (FSW) is a suitable technology for joining dissimilar materials. As the process temperature during FSW typically does not exceed the solidus temperature, like in fusion welding, high quality joints can be produced with a minimum of intermetallic phases. A comprehensive description of the effective joining mechanisms of friction stir welded dissimilar material joints is still subject of research. In this study the results of an analysis of the effect of the pin length, which is supposed to have a significant influence on the characteristics of the joining mechanisms, are presented. Especially the influence on the bonding conditions and the mechanical properties of the joints has been investigated. For this purpose combinations of aluminum and titanium have been welded with varying pin length at different rotational speeds. The experiments show that at a sufficient distance between the interface zone and the pin tip the bonding is realized by a substance-to-substance bond and microscopic form-fit. As this distance decreases, a visible macroscopic form-fit is generated. However, this macroscopic form-fit causes no significant elevation of the joint strength. First scanning transmission electron microscopy (STEM) images reveal an interfacial layer, which indicates a diffusion of the two materials.</jats:p