Corrosion resistance of AZ91 magnesium alloy after laser remelting treatment

Abstract

The main objective of the study was the modification of the surface layer of magnesium alloy by the CO₂ laser. The studied material was the commercial AZ91 magnesium alloy. The effectiveness of the alternations caused by the remelting process was verified on the basis of microscopic observation and corrosion investigations, i e, recording of potentiodynamic polarization curves, electrochemical noise measurements and hydrogen evolution rate measurements. For the adopted range of the treatment parameters, favourable changes were observed in the surface layer such as the refinement of structure and more uniform arrangement of individual phases. As a consequence of those favourable structural changes the improvement of the corrosion resistance of the alloy was achieved in comparison to its non-remelted equivalent. For the treated material corrosion rates expressed as corrosion current densities were at least three times lower than the appropriate values for the untreated alloy comparing them for the same period of samples immersion in the test solution. The obtained results have confirmed the effectiveness of the applied surface treatment resulting in favourable changes in the structure and corrosion properties of the AZ91 magnesium alloy.

Keywords

magnesium alloy / CO₂ laser / surface layer modification / corrosion

References

[1] Mordike B L, Ebert T. Magnesium: Properties-applicationspotential[J]. Mater. Sci. Eng. A, 2001, 302: 37-45.

[2] Braszczynska-Malik K N, Zawadzki I, Walczak W, et al. Mechanical Properties of High-pressure Die-casting AZ91 Magnesium Alloy[J]. Arch. Found. Eng., 2008, 8(4): 15-18.

[3] Dobrzanski L A, Tanski T, Cižek L, et al. Structure and Properties of Magnesium Cast Alloys[J]. J. Mater. Process. Tech., 2007, 192-193: 567-574.

[4] Piatkowski J, Binczyk F. Wlasciwosci i Zastosowanie Odlewniczych stopów Mg-Al[J]. Arch. Found., 2002, 2(4): 426-433.

[5] Blau P J, Walukas M. Sliding Friction and Wear of Magnesium Alloy AZ91D Produced by Two Different Methods[J]. Tribol. Int., 2000, 33: 573-579.

[6] Cižek L, Greger M, Pawlica L, et al. Study of Selected Properties of Magnesium Alloy AZ91 After Heat Treatment and Forming[J]. J. Mater. Process. Tech., 2004, 157-158: 466-471.

[7] Easton M, Beer A, Barnett M, et al. Magnesium Alloy Applications in Automotive Structures, Magnesium for Automative Applications[J]. J. Met., 2008, 60(11): 57-62.

[8] Fajkiel A, Bialobrzeski A, Dudek P, et al. Nowoczesne Stopy Oraz Metody Odlewania Magnezu w Zastosowaniach Motoryzacyjnych[J]. Przeglad mechaniczny, 2009, 2: 30-36.

[9] Pardo A, Merino M C, Coy A E, et al. Corrosion Behaviour of Magnesium/Aluminium Alloys in 3,5 wt% NaCl[J]. Corros. Sci., 2008, 50: 823-834.

[10] Liu M, Uggowitzer J, Nagasekhar A V, et al. Calculated Phase Diagrams and the Corrosion of Die-cast Mg-Al Alloy[J]. Corros. Sci., 2009, 51: 602-619.

[11] Mondal A K, Kumar S, Blawert C, et al. Effect of Laser Surface Treatment on Corrosion and Wear Resistance of ACM720 Mg Alloy[J]. Surf. Coat. Tech., 2008, 202: 387-398.

[12] Chakraborty Banerjee P, Singh Raman R K, Durandet Y, et al. Electrochemical Investigation of the Influence of Laser Surface Melting on the Microstructure and Corrosion Behaviour of ZE41 Magnesium Alloy-An EIS Based Study[J]. Corros. Sci., 2011, 53: 1505-1514.

[13] Zhang Y, Chen J, Lei W, et al. Effect of Laser Surface Melting on Friction and Wear Behavior of AM50 Magnesium Alloy[J]. Surf. Coat. Tech., 2008, 202: 3175-3179.

[14] Jun Y, Sun G P, Jia S S. Characterization and Wear Resistance of Laser Surface Melting AZ91D Alloy[J]. J. Alloy. Compd., 2008, 455: 142-147.

[15] Khalfaoui W, Valerio E, Masse J E, et al. Excimer Laser Treatment of ZE41 Magnesium Alloy for Corrosion Resistance and Microhardness Improvement[J]. Opt. Laser. Eng., 2010, 48: 926-931.

[16] Coy A E, Viejo F, Garcia-Garcia F J, et al. Effect of Excimer Laser Surface Melting on the Microstructure and Corrosion Performance of the Die Cast AZ91D Magnesium Alloy[J]. Corros. Sci., 2010, 52: 387-397.

[17] Dutta Majumdar J, Galun R, Mordike B L, et al. Effect of Laser Surface Melting on Corrosion and Wear Resistance of a Commercial Magnesium Alloy[J]. Mater. Sci. Eng. A, 2003, 361: 119-129.

[18] Zhang T, Liu X, Shao Y, et al. Electrochemical Noise Analysis on the Pit Corrosion Susceptibility of Mg–10Gd–2Y–0.5Zr, AZ91D Alloy and Pure Magnesium Using Stochastic Model [J]. Corros. Sci., 2008, 50: 3500-3507.

[19] Zhang T, Shao Y, Meng G, et al. Electrochemical Noise Analysis of the AZ91D Magnesium Alloy in Alkaline Chloride Solution[J]. Electrochim. Acta, 2007, 53: 561-568.

[20] Friedrich H E, Mordike B L. Magnesium Technology: Metallurgy, Design Data, Applications[M], 2006 Berlin Heidelberg: Springer-Verlag.