## 4 Conclusions  
The article presents the results of the analysis of the effect of heat treatment of EN AW-6082 aluminium alloy sheet on the quality of drawpieces and formability of the material during the incremental sheet-forming process. The influence of additional heat treatment on the microstructure and mechanical properties of the drawpieces was also analysed. Based on the results, the following conclusions can be drawn:  
* Incremental forming had no effect on the size and number of the observed precipitates in the material. However, additional heat treatment after forming contributed to the observation of additional precipitates in the test materials, especially in the case of drawpieces made from solutionised sheet metal and sheet metal that was aged after the ISF process. * The hardening state of the workpiece material had a significant effect on the formability of the material in the ISF process. It was found that with the increase in the strength  
Figure 18: Photograph of the inner surface of the drawpiece with the linear cyclic grooves the distribution of which mainly depends on the vertical step size and tool path strategy. of the material (from the O condition to the T6 tempering state), the value of the limit-forming angle of the drawpiece wall decreased from 69\({}^{\circ}\) (for annealed sheet) to 61\({}^{\circ}\) (for artificially aged material), which was also associated with a decrease in the plasticity of the material. * As a result of incremental forming, the strength properties and hardness of the ISFed pyramids increased, despite the temperature increase at the contact area between the forming tool and the sheet metal to 130 \({}^{\circ}\)C. This was due to the dominant influence of work hardening on the material properties after forming. The greatest increase was observed for the drawpiece made of annealed sheet metal. In the case of material in the T6 condition, the lowest values of the limit-forming angle were obtained and, consequently, the lowest increase in material strength. * Additional heat treatment after forming contributed to the increase in strength and hardness properties only in the case of drawpieces made of solutionised workpiece metal (and naturally aged after forming) and naturally aged workpiece material (and artificially aged after forming). In these materials, further precipitation hardening of the EN AW-6082 aluminium alloy occurred. In the remaining cases, especially for the T6 + T6 material, there was a decrease in strength, which may be related to the ageing of the material as a result of excessively long heating at 170 \({}^{\circ}\)C (for 6 h). * The surface roughness of the walls of the drawpieces was higher than that of the sheet metal in the as-received state, especially when measured in the direction parallel to the drawpiece wall axis. This was related to the ISF process conditions, especially the vertical step size. The use of a lower vertical stem size value could contribute to lower values of the Ra and Rz parameters. A hardened state of material has a significant impact on the degree of deformation in the ISF process. The forming of annealed sheets (O condition) contributes to obtaining drawpieces under a higher forming angle, but their strength properties are lower than those of other hardened states of material, despite work-hardening and additional heat treatment. On the other hand, sheets made from EN AW-6082-T6 aluminium alloy allow for obtaining drawpieces of high strength, but with a lower height than in the other cases. The most optimal case seems to be the manufacturing of drawpieces by incremental forming processes, from sheets that were subjected to solutionizing immediately before ISF and then additionally naturally aged after forming. A sufficiently high strength of the drawpieces material with relatively good formability can also be ensured by the strategy of forming EN AW-6082-T4 sheets, which are then subjected to artificial ageing. Conceptualization, L.K. and K.Z. ; methodology, L.K. and M.B. ; validation, K.Z. and T.T.