Microstructural Evolution of Cold-Rolled AA7075 Sheet during Solution Treatment

Effects of Heating Rates on Microstructural Evolution of Hot Extruded 7075 Aluminum Alloy in the Semi-Solid State and Thixotropic Deformation Behavior

The non-dendritic microstructure plays a crucial role in determining the rheological properties of semi-solid alloys, which are of the utmost importance for the successful industrial application of the thixoforging process. To further understand the impact of the reheating process on the evolution of microstructure and thixotropic deformation behavior in the semi-solid state, a hot extruded and T6 treated 7075 aluminum alloy was reheated to the selected temperature ranges using varying heating rates. Subsequently, thixo-compression tests were performed. The study found that during reheating and isothermal holding, the elongated microstructure of the as-supplied alloy can transform into equiaxed or spherical grains. The presence of recrystallized grains was found to be closely linked to the penetration of the liquid phase into the recrystallized grain boundaries. Furthermore, it was observed that higher heating rates resulted in smaller grain sizes. The thixotropic flow behavior of the alloy with various microstructures was analyzed using the true stress-strain curves obtained by thixo-compression experiments, which exhibited three stages: a rapid increase in true stress to a peak value, followed by a decrease in true stress and a steady stress until the end of compression. The stress fluctuated with strain during the formation of the slurry at a strain rate of 10 s-1, indicating the significant role of strain rate in material flow during semisolid formation.

Microstructures and Mechanical Properties of Al-Zn-Mg-Cu Alloys under Multi-Directional Severe Strain and Aging

Microstructure is a significant factor that influences the mechanical properties of alloys. The effect of multiaxial forging (MAF) and subsequent aging treatment on the precipitated phases of Al-Zn-Mg-Cu alloy remains unclear. Therefore, an Al-Zn-Mg-Cu alloy was processed by means of solid solution and aging treatment, and MAF and aging treatment in this work, and the composition and distribution of precipitated phases were characterized in detail. The MAF results for dislocation multiplication and grain refinement were found. The high density of dislocation greatly accelerates the nucleation and growth of precipitated phases. Thus, the GP-zones almost transform into precipitated phases during subsequent aging. The MAF and aging alloy has more precipitated phases than the solid solution and aging treated alloy. The precipitates on the grain boundary are coarse and discontinuously distributed due to dislocation and grain boundary promoting the nucleation, growth and coarsening of the precipitates. The hardness, strength, ductility and microstructures of the alloy have been studied. Without compromising the ductility much, the MAF and aging alloy has higher hardness and strength, with values of 202 HV and 606 MPa, respectively, and an appreciable ductility of 16.2%.

Surface Roughness Evaluation in Thin EN AW-6086-T6 Alloy Plates after Face Milling Process with Different Strategies

Lightweight alloys made from aluminium are used to manufacture cars, trains and planes. The main parts most often manufactured from thin sheets requiring the use of milling in the manufacturing process are front panels for control systems, housing parts for electrical and electronic components. As a result of the final phase of the manufacturing process, cold rolling, residual stresses remain in the surface layers, which can influence the cutting processes carried out on these materials. The main aim of this study was to verify whether the strategy of removing the outer material layers of aluminium alloy sheets affects the surface roughness after the face milling process. EN AW-6082-T6 aluminium alloy thin plates with three different thicknesses and with two directions relative to the cold rolling process direction (longitudinal and transverse) were analysed. Three different strategies for removing the outer layers of the material by face milling were considered. Noticeable differences in surface roughness 2D and 3D parameters were found among all machining strategies and for both rolling directions, but these differences were not statistically significant. The lowest values of Ra = 0.34 µm were measured for the S#3 strategy, which asymmetrically removed material from both sides of the plate (main and back), for an 8-mm-thick plate in the transverse rolling direction. The highest values of Ra = 0.48 µm were measured for a 6-mm-thick plate milled with the S#2 strategy, which symmetrically removed material from both sides of the plate, in the longitudinal rolling direction. However, the position of the face cutter axis during the machining process was observed to have a significant effect on the surface roughness. A higher surface roughness was measured in the areas of the tool point transition from the up-milling direction to the down-milling direction (tool axis path) for all analysed strategies (Ra = 0.63–0.68 µm). The best values were obtained for the up-milling direction, but in the area of the smooth execution of the process (Ra = 0.26–0.29 µm), not in the area of the blade entry into the material. A similar relationship was obtained for analysed medians of the arithmetic mean height (Sa) and the root-mean-square height (Sq). However, in the case of the S#3 strategy, the spreads of results were the lowest.