## 3 Results and Discussion  
### Mechanical Properties of Sheet Metals  
Figure 3a-d show tensile stress-strain curves depending on the material hardening state and orientation relative to the rolling direction. Table 5 presents the values of the mechanical properties of the test materials. The obtained values of mechanical parameters for each sample orientation and tempering designation were similar. Solutionising and artificial ageing (T6) increase strength properties while reducing plastic properties compared to the annealed state. A slight anisotropy of mechanical properties was observed (Figure 4a-d). In the case of elongation, EN AW-6082-O, EN AW-6082-W and EN AW-6082-T4 sheets exhibit similar values of elongation range from 26 to 28% (Figure 5). Only in the case of the artificially aged material (T6) were significantly lower elongation values (A = 9.4%) observed. Artificial ageing also contributed to significantly higher strength properties of the material (Figure 6). At the same time, a small plasticity reserve could be observed, which is the difference between the UTS and the YS. A small value of this parameter means a low tendency of the material for deep drawing. For the solution-heat-treated (W) and naturally aged (T4) materials, similar values of mechanical properties were found. These parameters had a significant influence on the process of incremental sheet forming.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Temper Designation** & **Description** & **Ay\%** & **Ay\%** & **Ay\%** \\ \hline O + T6 & Annealed sample after forming, solutionizing and artificial ageing (sample placed in a furnace at 575 \({}^{\circ}\)C for 2 h and artificially aged at 170 \({}^{\circ}\)C for 6 h) & \\ W + T4 & Solution-heat-treated sample after forming, solution heat treated and naturally aged (sample placed in a furnace at 575 \({}^{\circ}\)C for 2 h and naturally aged at room temperature for 30 days) & \\ W + T6 & Solution-heat-treated sample after forming, solution heat treated and artificially aged (sample placed in a furnace at 575 \({}^{\circ}\)C for 2 h and artificially aged at 170 \({}^{\circ}\)C for 6 h) & \\ T4 + T6 & Solution-heat-treated and naturally aged sample after forming, solution-heat-treated and artificially aged sample & \\ T6 + T6 & Solution-heat-treated and artificially aged sample after forming, solution-heat-treated and artificially aged sample & \\ \hline \end{tabular}
\end{table}
Table 4: Conditions of additional heat treatment of selected samples after forming.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Temper Designation** & **Sample Orientation, \({}^{\circ}\)** & **YS, MPa** & **UTS, MPa** & **Ag\%** & **A\%** \\ \hline \multirow{4}{*}{O} & 0 & 43.2 & 128.4 & 23.0 & 28.8 \\  & 45 & 43.5 & 127.1 & 21.6 & 27.4 \\  & 90 & 45.0 & 127.3 & 22.0 & 28.0 \\  & Average & 43.8 & 127.5 & 22.1 & 27.9 \\ \hline \multirow{4}{*}{W} & 0 & 145.7 & 265.7 & 2  
Figure 4: Influence of sample orientation and processing conditions of EN AW-6082 aluminium alloy on (**a**) YS, (**b**) UTS, (**c**) A\({}_{\rm g}\) and (**d**) A.  
Figure 3: Tensile stress-strain curves of aluminium alloys: (**a**) EN AW-6082-O, (**b**) EN AW-6082-W, (**c**) EN AW-6082-T4 and (**d**) EN AW-6082-T6.