Corrosion properties of Al/steel-hybrid joints manufactured by ultrasound enhanced friction stir welding (USE-FSW)Thursday (09.11.2017) 09:15 - 09:35 Part of:
The demand for environment-friendly products and production is steadily increasing and the realization of innovative lightweight structures is of great interest. In this regard aluminium/ steel is a beneficial material combination. Fusion welding of these dissimilar metals is in the most cases difficult or even impossible because of different melting points of the materials and the development of undesirable brittle intermetallic phases. This often leads to joint strengths considerable below the tensile strength of the base materials. Therefore 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 as shown in  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. 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 investigate the corrosion activity of the base alloys and the nugget phase separately. A distinct influence of the additional ultrasound on the amount of intermetallic phases, which could be identified by SEM/EDX, was observed.
 S. Benfer, B. Straß, G. Wagner and W. Fürbeth, Surface and Interface Analysis, Vol. 48(8), 843-852, 2016; DOI 10.1002/sia.5871.