Superplastic deformation of thin sheets is widely used in aerospace, automotive and other industries. In this paper, a mathematical model of plane strain superplastic pressure forming of a sheet specimen into a die is proposed. A die under consideration has a shape of a long box with an isosceles trapezoid cross section, but the model can be generalized for more complex die shapes. It is assumed that sticking happens between a shell and a die and thickness remains unchanged once contact occurs. The process of forming was divided into different phases, which are determined by the die geometry. For each phase, ordinary differential equations for thickness were derived along with the initial conditions. Solutions of obtained ODEs allow estimating the shell thickness at any point of a specimen as a function of coordinate along walls of the die and to determine the duration of each superplastic pressure forming phase for a given pressure-time function. Norton’s power law was used as a constitutive equation. Due to the simplicity of Norton`s law it is possible to solve some of ODEs analytically. The proposed model can be used with other types of constitutive relations, in particular with relations that include microstructure parameters etc. The superplastic forming of a Ti-6Al-4V titanium alloy sheet for the piecewise pressure-time function has been modelled. Some special cases of die geometry are analyzed.
Enhancing the strength, hardness, and wear resistance of aluminum alloys can be done through composite forming. According to the methods of production, composites can be classified into two types: ex situ and in situ composites. In ex situ composites, the reinforcing particles do not interact with the matrix, whereas in in situ composites, a chemical reaction occurs between the reinforcing particles and the matrix. Friction stir processing (FSP) is a promising approach to forming in situ composites, as it involves the frictional mixing of solid-state metal through the combined rotational and linear movement of the tool. The aim of this work was to study the impact of multi-pass FSP on the microstructure and microhardness of the in situ composite formed on the surface of an AA6063 alloy with pre-incorporated NiO particles. For this purpose, 4-, 10-, and 20‑pass FSP of AA6063 alloy sheets with grooves filled with fine NiO powder were performed. The chemical reaction between NiO and the aluminum matrix leading to the formation of Al3Ni and Al2O3 was studied using EDS, EBSD and X-ray diffraction techniques. It was found that the quantity of Al3Ni and Al2O3 particles increased with the number of FSP passes. The maximum surface microhardness of 253 HV is reached after 10 passes. As the number of FSP passes increases, the grain / subgrain sizes of the aluminum matrix decrease. After 10 passes, the grain / subgrain sizes stabilize at a level of 0.8 – 0.9 μm.