Hybrid joints manufactured by ultrasound enhanced friction stir welding (USE-FSW) - corrosion properties
S. Benfer, W. Fürbeth, M. Thomä, G. Wagner, B. Straß, B. Wolter
IOP Conf. Series: Materials Science and Engineering 181 (2017) 012004; DOI: 10.1088/1757-899X/181/1/012004
To realize lightweight structures of material combinations like aluminum/magnesium and aluminum/steel an Ultrasound Enhanced Friction Stir Welding (USE-FSW) process was used. This process has a beneficial influence on the resulting microstructure (elimination of the brittle intermetallic phase Al3Mg2 as coherent layer) and the mechanical properties (increased tensile strength) of Al/Mg-joints and was now also applied for Al/steel-hybrid joints. Besides the mechanical properties the corrosion properties of the hybrid joints may play a significant role concerning the later use of the hybrid materials. Therefore, the corrosion properties of various hybrid joints have been investigated by different methods. With the Scanning Kelvin Probe (SKP) Volta potential differences between the base alloys and the welded area were investigated in air. The two-dimensional color-plots illustrate not only the Volta potential differences between the different phases but also their oxidation properties in air during the measurement time. Electrochemical measurements (open circuit potential and potentiodynamic polarization) have been carried out for the investigation of the corrosion properties of the FSW and USE-FSW hybrid joints in 0.5 molar NaCl solution. A three electrode setup within a mini-cell was used to enable measurements on different areas of the joints. This allows to observe the corrosion activity of the base alloys and the nugget phase separately. Differences between Al/steel-hybrid joints processed with and without ultrasound enhancement are discussed and compared with Al/Mg-hybrids.