UNDERSTANDING THE CORROSION BEHAVIOR OF FRICTION-STIR-WELDED DIE CAST AM50 AND AZ31-H24 MAGNESIUM ALLOYS

Mg alloys are attractive candidates to replace aluminum and steel for many structural applications. However for these applications, the matter of joining should be referred. Conventional fusion welding process creates porosity which deteriorates the mechanical properties and reduces corrosion resistance. Thus, Friction Stir Welding (FSW) which has not exhibited complications mentioned above [1], is one of the most promising methods which should be explored more thoroughly. FSW process results in dynamic recrystallization which might be continuous or discontinuous [2], effecting the microstructure and final physical and chemical properties. Therefore, it is of outmost importance to characterize the process and generalize its influence depending on an alloy type.

In current research, the influence of the FSW on the corrosion behavior of die cast AM50 and wrought AZ31-H24 Mg alloys was studied. Due to the intimate link among the properties and the microstructure of the materials, the difference in the corrosion behavior was attributed to the microstructural changes occurred in these alloys. Estimated value of the Stacking Fault Energy (SFE) was connected to the different evolution of the microstructure in both studied alloys. It was concluded that due to the higher SFE - recrystallization process occurring in AM50 was continuous, manifested by the rearrangement of dislocation and grain subdivision. Lower SFE in AZ31 led to discontinuous recrystallization through the rotation of twins, turning them into low angle grain boundaries.

[1] R.C. Zeng, J. Chen, W. Dietzel, R. Zettler, J.F. dos Santos, M. Lucia Nascimento, Corros. Sci. 51 (2009) 1738–1746.

[2] M.O. Pekguleryuz, K.U. Kainer, A.A. Kaya, Fundamentals of magnesium alloy metallurgy, Cambridge, 2013.