Results and Discussion 
Different w/t ratios, obtained by changing the thicknesses of AlMg6.5 sheets (in the range of 
2.25mm to 0.75mm), were accompanied by certain grain size or appropriate mechanical properties 
variation. The tensile properties and the average grain size produced by different cold rolling 
reductions (from 5% to 70%) and subsequent annealing (at 320°C/3h) are summarized in Table 2. 
After 5% and 10% reductions and annealing at 320°C/3h, the structures were coarse grained, but 
not fully recrystallized (as indicated in Table 2). After higher degrees of cold rolling reductions 
(from 15% to 70%) and subsequent annealing, all the samples have shown fully recrystallized 
structures. The gradual yield stress (YS) increasing from ~147MPa to ~188MPa, that is caused by 
increasing the rolling reductions or by the appropriate grain sizes refinement, reflects the Hall-Petch 
type relation [1], about the grain size effect on the flow stress (Table 2). 
Table 2: Width to thickness ratios, grain sizes and tensile properties of AIMg6.5 sheet samples 
viii 28 x 53 
pm i] 
UTS, MPa 346.4 [342.0 [342.8 | 344.0 | 346.0 | 347.0 | 347.8 [349.2 | 
as-received material 
") Non-fully recrystallized structure 
Previous study on the tested AlMg6.5 alloy 
0.40- sheet [10] has shown that room temperature 
tensile deformation is characterized by 
035- work hardening exponent (n) intensive serrated flow, which is induced by 
—a—Bad AD A dynamic strain aging (DSA) process. It was also : 
0:30: 5 a observed that the straining of the tested alloy 
0.25 strain to failure (6) a : under serrated flow condition was terminated 
53: by shear fracture occurence, just beyond the 
0.20 EB — ger maximum load [10], as it was noticed in other - 
uniform strain (,) Al-Mg alloys with lower Mg content [6-9]. IM 
0.15 Fig.1 illustrates the relation between uniform low 
- strain (nom), Strain to failure (gf) and work I; 
010+ nn ee hardening exponent (n) in the tested AIMg6.5 : 
10 15 20 25 30 35 40 45 50  glloy sheet. It has shown that the uniform strain 
grain size, pm and strain to failure were very close, gnom~0.21 
Fig.l: The relationship between uniform and and €r~0.23, respectively, and also the post 
total strain and work hardening exponent under uniform elongation (elongation due to neck 
serrated flow condition in AIMg6.5 alloy sheet. growth) is neglected, ie. &r€nom~0, as the 
fracture occurs just beyond the maximum load. 
It can be seen that the ductility parameters 
(nom, € and n) were independent on the grain size and also on the specimen geometry (Fig.1). The 
work hardening exponent (rn) calculated using the expression o=K-€", was also found rather 
independent on the grain size (as well as on the specimen geometry). An average value of n~0.31 
was obtained for fully recrystallized structure, and for non-fully recrystallized structure it was 
decreased to value of n~0.27 (as indicated by the arrows in Fig.1). It can be supposed that negative 
strain sensitivity (SRS) in the tested AIMg6.5 alloy sheet, m=-0.01+-0.02 [11], also causes the 
constriction between uniform strain and strain to failure (Fig.l) and promotes shear failure 
occurrence just beyond the maximum load along the planes of localized deformation, within shear 
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