INFLUENCE OF FRICTION STIR WELDING ( FSW) ON MECHANICAL AND CORROSION PROPERTIES OF AW-7020M AND AW-7020 ALLOYS

Abstract

Friction welding associated with mixing the weld material (FSW - Friction Stir Welding ) is an alternative to MIG and TIG welding techniques for Al-alloys. This paper presents experimental results obtained from static tension tests on specimens made of AW-7020M and AW-7020 alloys and their joints welded by using FSW method carried out on flat specimens, according to Polish standards: PN-EN ISO 4136:2011 and PN-EN ISO 6892-1:2010. Results of corrosion resistance tests are also presented. The tests were performed by using the electrochemical impedance spectroscopy (EIS). EIS measurement was conducted with the use of three-electrode system in a substitute sea water environment (3,5% NaCl - water solution). The impedance tests were carried out under corrosion potential. Voltage signal amplitude was equal to 10mV, and its frequency range - 100 kHz ÷ 0,1 Hz. Atlas 0531 EU&IA potentiostat was used for the tests. For the tested object an equivalent model was selected in the form of a substitute electric circuit. Results of the impedance spectroscopy tests are presented in the form of parameters which characterize corrosion process, as well as on Nyquist’s graphs together with the best-fit theoretical curve. Analysis of the test results showed that the value of charge transfer resistance through double layer, Rct, for the FSWwelded specimen, was lower than that for the basic material, and that much greater difference was found in the case of AW-7020M alloy. The impedance spectroscopy tests showed that both the FSW-welded joints and basic material of AW 7020M and AW-7020 alloys were characterized by a good resistance against electrochemical corrosion in sea water environment, and that FSW –welded joints revealed a greater corrosion rate. The performed tests and subject-matter literature research indicate that application of FSW method to joining Al-alloys in shipbuilding is rational.