Influence of friction stir welding (FSW) on mechanical and corrosion properties of AW-7020M and AW-7020 alloys
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 FSW- welded 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
- 1. Bugłacki H., Neser G.: Properties of welded Al-alloys applicable in shipbuilding (in Polish). Biuletyn Instytutu Spawalnictwa w Gliwicach (Bull. of Welding Institute, Gliwice), No. 5/2001.
- 2. Cudny K., Puchaczewski N.: Metal alloys for ship hull structures and ocean engineering objects ( in Polish). Wydawnictwo Politechniki Gdańskiej ( Publishing House of Gdańsk University of Technology), Gdańsk 1995.
- 3. Czechowski M.: Effect of anodic polarization on stress corrosion cracking of some aluminium alloys, Advances in Materials Science, Vol 7, pp. 13-20, number 1(11) 2007.
- 4. Czechowski M.: Low-cycle fatigue of friction stir welded Al-Mg alloys. Journal of Materials Processing Technology, 164-165(2005), pp. 1001÷1006.
- 5. Dudzik K., Czechowski M.: Analysis of possible shipbuilding application of Friction Stir Welding (FSW) method to joining elements made of AlZn5Mg1 alloy. Polish Maritime Research No.4/2009.
- 6. Dudzik K., Jurczak W.: Influence of friction stir welding on corrosion properties of AW-7020M alloy in sea water. Advances in Materials Science, Vol. 15, No. 1 (43), March 2015.
- 7. Ferraris S, Volpone L.M.: Aluminium alloys in third millennium shipbuilding: materials, technologies, perspectives, The Fifth International Forum on Aluminium Ships, Tokyo, 2005.
- 8. Jurczak W.: Problems and prospects of Al-alloys in their application to marine structures ( in Polish) . Zeszyty naukowe Akademii Marynarki Wojennej ( Scientific bulletins of Polish Naval University ), Vol. 41 , No. 4 (183) 2010, Gdynia 2010.
- 9. Jurczak W.: The effect of heat treatment on the structure and corrosion resistance of Al-Zn-Mg alloys. Polish Maritime Research , Vol. 15 , No.4(58)/2008.
- 10. Lahti K.: FSW – possibilities in shipbuilding, Svetsaren, The ESAB Welding and Cutting Journal, Vol. 58, No.1/2003.
- 11. Mazzolani F. M.: Aluminium Alloy Structures (second edition), E&FN SPON, an imprint of Chapman & Hall, London 1994.
- 12. Pietras A., Zadroga L., Łomozik M.: Characteristics of weld produced by using friction welding technique associated with mixing weld material (FSW) ( in Polish), Biuletyn instytutu spawalnictwa w Gliwicach ( Bul. of Welding Institute , Gliwice), No.3/2003.
- 13. Sharma C., Dwivedi D. K., Kumar P.: Effect of welding parameters on microstructure and mechanical properties of friction stir welded joints of AA7039 aluminum alloy. Materials and Design, 36 (2012).
- 14. Trzaska M., Trzaska Z.: Electrochemical impedance spectroscopy in material engineering ( in Polish). Oficyna Wydawnicza Politechniki Warszawskiej (Publishing House of Warsaw University of Technology), Warsaw, 2010.
- 15. ASTM G 3 Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing. ?
- 16. ASTM G 106 Standard Practice for Verification of Algorithm and Equipment for Electrochemical Impedance Measurements.