Search

Wire and arc additive manufacturing of aluminium-ceramic composites shows great potential to produce high strength materials. By incorporation of nanoparticles in the feedstock wire, fine-grained material with low susceptibility for solidification cracking and enhanced strength can be obtained. In fact, this study utilised the novel screw extrusion method to prepare an aluminium alloy containing TiC nanoparticles. The commercial aluminium alloy AA5183 was selected for WAAM to assess and benchmark the effects of screw extrusion and TiC. The materials have been assessed in terms of microstructure, porosity content and mechanical properties. The presence of TiC reduced the average grain diameter by 70%, while Vickers hardness increased with 13%. However, number of pores per unit volume increased by one order of magnitude. The porosity is believed to stem from hydrogen introduced in the AA5183-material through screw extrusion processing, in addition to hydrogen trapping and pore nucleation on TiC nanoparticles.

Co-extrusion method is used for production of a dual Aluminum rod. The surface layer material for co-extrusion is prepared by rapid solidification process. The alloys Al-4.5Mg-1.0Ag (wt%) and Al-4.5Mg are selected as the surface and the bulk materials, respectively, and are co-extruded at high temperature range (450-480°C). The microstructures of rapid solidified Al in co-extruded rod consist of small grains (50 µ m) and some small particles (0.1-1 µ m). A proper annealing on the extruded rod increases the surface hardness more than 30%. Since the co-extruded material contains small T-phase particles, this increase in hardness indicates precipitation of a metastable Mg-Ag phase or a Mg-Ag-Al phase at 160°C during annealing. [ABSTRACT FROM AUTHOR]

Plastic deformation studies of a peak-aged AA6082 alloy by means of tensile tests at 77 K and 295 K, and related microstructure characteristics obtained by Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD), Transmission Electron Microscopy (TEM) and Atom Force Microscopy (AFM), revealed new results. A simultaneous improvement in ductility and strength occurred at 77 K, but not at 295 K. A higher work hardening accompanied by a more homogeneous slip mode explained the improved properties at 77 K. Pre-stretching at these two temperatures and subsequent tensile testing at room temperature revealed a marked yield point. However, pre-stretching at 77 K exhibited a slightly higher room temperature yield strength and ductility than the condition pre-stretched at 295 K. Annealing after pre-stretching improved ductility and reduced the magnitude of the yield point. Pre-stretching at 77 K and subsequent annealing introduced somewhat higher strength and ductility as compared to the counterpart pre-stretched at 295 K. The observed mechanical behaviour and associated phenomena were directly linked to microstructure characteristics such as deformation substructure history, slip localization, dislocation density and the precipitate β ' /β '' ratio. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical properties of a wide range of aluminium alloys are compared after being subjected to severe plastic deformation (SPD), i.e. equal channel angular pressing (ECAP). Alloys involved are AlMg, AlMn, AlMgSi, and AlMgSc. The effect of SPD on mechanical properties is mostly beneficial with age-hardenable alloys, whereas non-age-hardenable alloys tend to be relatively less reacting to SPD as compared to conventional processing. Finally, some challenges in regard to commercialization will be discussed briefly. [Copyright &y& Elsevier]

Abstract: Deformation banding and accompanying texture component rotations towards more stable orientations played an important role to grain sub-division and during the development of new high angle grain boundaries. The low energy dislocation structure (LEDS) approach predicted deformation band size in close correspondence to the present observations, and the proposed grain refinement mechanism. Formation of twin boundaries seemed to play an important role at strains beyond two. [Copyright &y& Elsevier]

Processing of aluminum alloys by wire arc additive manufacturing (WAAM) gained significant attention from industry and academia in the last decade. With the possibility to create large and relatively complex parts at low investment and operational expenses, WAAM is well-suited for implementation in a range of industries. The process nature involves fusion melting of a feedstock wire by an electric arc where metal droplets are strategically deposited in a layer-by-layer fashion to create the final shape. The inherent fusion and solidification characteristics in WAAM are governing several aspects of the final material, herein process-related defects such as porosity and cracking, microstructure, properties, and performance. Coupled to all mentioned aspects is the alloy composition, which at present is highly restricted for WAAM of aluminum but received considerable attention in later years. This review article describes common quality issues related to WAAM of aluminum, i.e., porosity, residual stresses, and cracking. Measures to combat these challenges are further outlined, with special attention to the alloy composition. The state-of-the-art of aluminum alloy selection and measures to further enhance the performance of aluminum WAAM materials are presented. Strategies for further development of new alloys are discussed, with attention on the importance of reducing crack susceptibility and grain refinement. [ABSTRACT FROM AUTHOR]

Bulk nanostructured (NS) metallic materials usually have high strength but extremely low ductility. In this study, we successfully prepared a bulk NS binary Al–7 Mg alloy possessing both high strength and high uniform ductility, approaching ∼600 MPa and ∼14%, respectively, by utilizing room temperature equal channel angular pressing (ECAP) combined with inter-pass annealing. The mechanism that governs the high ductility in the alloy and especially the role of the high Mg solute concentration was explored in terms of microstructure analysis. [ABSTRACT FROM AUTHOR]

Abstract: Metallic materials processed by severe plastic deformation generally possess very high strength but a rather low uniform elongation, usually <5%. In the present Al–7Mg alloy processed by room temperature equal channel angular pressing combined with inter-pass annealing, impressive combination of high ductility (elongation~14.5%) and high strength (UTS~600MPa) was achieved. The high ductility was rationalized by an enhanced work hardening originated from the pronounced dynamic strain aging effect and a bimodal grain structure. The high strength was mainly due to a prominent grain refinement and high dislocation density. [Copyright &y& Elsevier]

An Al-0.4Fe-0.15Zr-0.25Er alloy was processed by high pressure torsion (HPT) at room temperature in order to explore the evolution of property, microstructure and texture during HPT. The evolution of microstructure revealed by electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS). The microhardness increases with increasing strain up to 60 HV at a strain of about 12, and then decreases slightly to a steady stage. HPT processing leads to a significant increase (>100%) in microhardness at expense of a slight reduction (<3%) in electrical conductivity. The synchronous improvement in microhardness and electrical conductivity is obtained after aging. A significant decrease from 40 μm to 600 nm in grain size is observed after HPT deformation for 5 turns and beyond. HPT processing might accelerate the dissolution of the Al 3 (Zr,Er) precipitate. The A- {111} <110>and C- {001} <110> texture components are dominating after 0.25 turn. After 1 turn, the A and C components weaken, and the {112} <111> new component appears. The texture is weak and close to random due to recovery and recrystallization after 5 turns and beyond. • HPT processing leads to a significant increase in microhardness at expense of a slight reduction in electrical conductivity. The synchronous improvement in microhardness and conductivity is obtained after aging. • The grain size was significantly decreased from 40 μm to 600 nm by HPT. HPT might accelerate the dissolution of the Al 3 (Zr,Er) precipitate. [ABSTRACT FROM AUTHOR]