Effect of a trace of sodium on the high temperature ductility of 5083 aluminum alloy

In order to clarify the effect of a trace sodium at high temperature ductility of 5083 aluminum alloys, elevated temperature tensile tests and microstructure observations were carried out in 5083 alloys containing various amounts of sodium (1-237 ppm). It was shown that sodium content has little effect on grain size and microstructure of 5083 alloys. The author detected sodium element at inclusions on grain boundaries in 5083 alloys containing 237 ppm of sodium using EDS. This suggests that a trace of sodium in 5083 alloys segregate at the inclusions. More than 7 ppm of sodium brought about ductility loss in 5083 alloys at 773 K regardless of grain size in a similar way as reported in 5183 alloys. The author showed that 16 ppm of sodium promote the nucleation of coarse voids during deformation in 5083 alloys. Thus, it is clear that a trace of sodium plays an important role in high temperature ductility loss. On the other hand, 237 ppm of sodium brought about severe embitterment even at room temperature. The result of fracture surface analysis indicates that such a large amount of sodium impurity induces room temperature embrit-tlement because of significant decohesion of precipitate-matrix interface resulting from sodium segregation. © 2016 The Japan Institute of Light Metals.