Microphotographs obtained by SEM observations revealed that fracture surfaces exhibit three 
different sizes of ductile dimples (Fig.3a,b). The large dimples are associated with coarse 
intermetallic Mg,Si-phase (1+10pum) and smaller ones associated with fine second-phase particles 
as (Fe, Mn)Alg and MnAl4 (0.05+0.5um) in the microstructure. It seems that in case of the thinner 
tensile specimen (/=0.75mm or w/t=8.3) with fully recrystallized structure, considerably coarser 
dimples were noticed (Fig.3b) than in the thicker specimen (/=2.25mm or w/r=2.8) (Fig.3a). It can 
be explained by different hydrostatic stress level in thinner and thicker sample, as it was obseved 
earlier [13]. The morphology of fracture surfaces in the tested alloy (Fig.3a,b) indicates that failure 
have started by void initiation as ductile dimple type, as it was observed in other Al-Mg alloys [2,6- 
9]. It was supposed that the failure does not propagate by voids growth and its coalescence, but it 
occurs by shearing along the planes of localized deformation (in shear bands or in PLC bands) and 
the post uniform elongation (due to voids growth) is neglected, as it has shown in Fig.1. 
Summary 
AlMg6.5 alloy sheet samples with different width to thickness ratios (w/r=2.5+8.3), were tested in 
uniaxial tension test. The sheet samples were produced by cold rolling to different thicknesses 
(=2.25mm to 0.75mm), and annealing at 320°C/3h. The ductility parameters were independent on 
the specimen geometry, and also on the grain size variation, but their relations were influenced by 
dynamic strain aging (DSA) process (&r-€hom~0 and epom<r). 
The tensile failure appearance was analyzed by scanning electron microscope (SEM). SEM 
observations have shown that the fracture in the tested material is transgranular ductile dimple type, 
which occurs by shear mode. The position of fracture surfaces to tensile axis depends on the 
specimen geometry (through w/t ratio variation, which reflects the transition from plane stress to 
plane strain condition) and also on the grain size (through the grain size effect on the intensity of 
PLC bands appearance). For fine-grained fully recrystallized structure, with high w/ ratio 
(w/t=6.3+8.3 - approximate plane stress condition), the fracture occurs at ~60-70° to the tensile axis, 
parallel to the PLC bands, which are very intensive in that case. For coarse-grained non-fully 
recrystallized structure, with low w/t ratio (w/f=2.5+5.0 - approximate plane strain condition), the 
appearance of PLC bands is less evident, and the fracture occurs at ~55° through the specimen 
thickness, and at 90° in respect to the tensile axis. 
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