Issue 35

A. Pawełek et alii, Frattura ed Integrità Strutturale, 35 (2016) 21-30; DOI: 10.3221/IGF-ESIS.35.03 27 (a) (b) (c) (d) Figure 8 : AE behavior and the course of external load: (a) up to all-out breaking and (b) exactly just before breaking of the Mg4Li5Al sample; (c) and (d) – corresponding SEM images. (a) (b) Figure 9 : Optical images illustrating the fully developed shear band (a) and the slip bands and microshear bands crossing over many grains (b) . Mg4Li4Zn alloys – tensile tests In order to investigate the role of alloy addition, e.g. of zinc instead aluminium, a Mg4Li4Zn alloy was chosen, especially because the plastic instability connected with the PL effect in these alloys is known in literature [19]. The results of the preliminary studies for these alloys are presented in Fig.10. The AE behavior and external stress are shown in Fig.10a for room temperature and in Fig.10b for 200ºC. The SEM images are presented respectively in Fig.10c,d, whereas in Fig.10e,f the SEM pictures are placed as additional observations and they correspond to the fracture at 400ºC. Unfortunately, when analysing Fig.10a,b it seems that the effect PL in Mg4Li4Zn alloys did not occur or it was not visible. There is by the reason that these alloys were prepared by casting of raw materials, whereas in work [19], where it was clearly visible, those alloys were prepared by extrusion followed with homogenization at 623K. On the other hand, the SEM pictures (Fig.10c,d,e and f) show that the character of fracture did not substantially change and it was mostly of intergranular type. Thus, it is necessary to carry on the research improving the technical aspects of the experiments (better