This study presents a comprehensive evaluation of the effects of multi-channel spiral twist extrusion (MCSTE) processing on the mechanical properties and structural evolution of AA5083. The structural evolution and texture developed were mapped by electron backscatter diffraction (EBSD) for three successive passes and compared with an as-annealed plate. An evaluation of the hardness and tensile properties was presented and correlated with the EBSD findings. The displayed EBSD results revealed that grain refinement was strongly associated with the presence of a high density of low-angle grain boundaries (LAGBs) after one pass, which developed into fine grains of less than 20 μm and high-angle grain boundaries (HAGBs) after three MCSTE passes. The three pass processing led to a 65% reduction in grain size. This reduction in grain size was coupled with an enhancement in the hardness and tensile properties. Additionally, the crystallographic texture study represented a slightly random texture due to the presence of intermetallic particles in AA5083. This study demonstrates the efficacy of MCSTE as a grain refinement tool.

The mechanical properties of Al castings are reduced by inclusions, particularly double oxide films, or bifilms, which are formed due to surface turbulence of the liquid metal during handling and/or pouring. These defects have been reported not only to decrease the tensile and fatigue properties of Al alloy castings, but also to increase their scatter. Recent research has suggested that the nature of oxide film defects may change with time, as the air inside the bifilm would react with the surrounding melt leading to its consumption, which may enhance the mechanical properties of Al alloy castings. In order to follow changes in the composition of the internal atmosphere of a double oxide film defect within an Al melt, a series of analogue experiments were carried out to determine the changes in gas composition of an air bubble trapped in a melt of commercial purity Al, subjected to stirring. The bubble contents were analysed using a mass spectrometer to determine their change in composition with time. Also, the solid species inside the bubbles solidified in the melt were analysed. The results suggested that first oxygen and then nitrogen inside the bubble were consumed, with consumption rates of 2.5x10^-6 and 1.3x10^-6 mol m^-2s^-1, respectively. Also, hydrogen diffused into the bubble from the melt at an average rate of 3.4x10^-7 mol m^-2s^-1, although the rate of H diffusion increased significantly after the consumption of most of the oxygen inside the bubble. Based upon these reaction rates the time required for a typical alumina bifilm to lose all its oxygen and nitrogen was determined to be just under 10 minutes.

Several physics-based models have been utilized in material design for the simulation and prediction of material properties. In this study, several machine-learning (ML) approaches were used to construct a prediction model to analyze the influence of equal-channel angular pressing (ECAP) parameters on the microstructural, corrosion and mechanical behavior of the biodegradable magnesium alloy ZK30. The ML approaches employed were linear regression, the Gaussian process, and support vector regression. For the optimization of the alloy’s performance, experiments were conducted on ZK30 billets using different ECAP routes, channel angles, and number of passes. The adopted ML model is an adequate predictive model which agreed with the experimental results. ECAP die angles had an insignificant effect on grain refinement, compared to the route type. ECAP via four passes of route Bc (rotating the sample 90° on its longitudinal axis after each pass in the same direction) was the most effective condition producing homogenous ultrafine grain distribution of 1.92 µm. Processing via 4-Bc and 90° die angle produced the highest hardness (97-HV) coupled with the highest tensile strength (344 MPa). The optimum corrosion rate of 0.140 mils penetration per year (mpy) and the optimum corrosion resistance of 1101 Ω·cm² resulted from processing through 1-pass using the 120°-die. Grain refinement resulted in reducing the corrosion rates and increased corrosion resistance, which agreed with the ML findings.

Wire arc additive manufacturing (WAAM) with high deposition rates has attracted industry interest for the demonstrated economic production of medium-to-large-scale metallic components. The structural integrity and mechanical properties of the built parts depend on the selection of the optimum deposition parameters and the tool path strategy. In this study, an alternate orthogonal deposition strategy was employed. The influence of the beads’ geometry and the associated heat input on the mechanical and structural behavior of mild steel (ER70S-6) were investigated. The influence of the bead width (BW) and the overlapping percentage (OP) between the adjacent beads on the average and layer-by-layer hardness of the blocks along the building direction were evaluated. Tensile strength was also characterized. The alternate orthogonal building strategy enhanced the geometrical uniformity of the built blocks and the microstructural isotropy along the building direction. Increasing the BW increased the total heat input per bead per layer, which significantly reduced the hardness and tensile strength of the built blocks by 19% and 17% compared to 8% and 7% when increasing the OP, respectively. Total heat input, number of heating cycles, and cooling rates triggered the phases formed, and their morphologies along the building direction were also characterized.