- Friction stir welding (FSW) allows to join Al and Mg alloys, which could hardly be welded by other techniques. Within the project a modified FSW process was developed, which uses additionally submitted power ultrasound during the joining of the Al‐cast and Mg‐cast alloys with the aim to improve the stirring in the welded area and to eliminate the formation of brittle intermetallic phases as coherent layers which reduce the attainable strength of the joints. To understand the development of the microstructure in the bonding zone a detailed analysis has been carried out. The resulting microstructure may influence the corrosion properties, which have been investigated by different methods. Voltapotential differences between the base alloys and the welded area were measured with the Scanning Kelvin Probe. Electrochemical measurements (open circuit potential, impedance spectroscopy and potentiodynamic polarization) were carried out at different positions on the hybrid joints by using an electrochemical minicell (∅ 3 mm). This allows to observe the passivation behavior and corrosion activity of the base alloys and the nugget phase separately. As expected the Mg alloy exhibits a much stronger corrosion in sodium chloride solution than the Al alloy. In the transitional area between the Mg alloy and the nugget phase the overall corrosion rate strongly increases while the corrosion of the nugget is reduced at the expense of the Mg alloy. Differences between hybrid joints processed with and without ultrasound support are discussed. Copyright © 2015 John Wiley & Sons, Ltd.
