Atomic diffusion by the vacancy defect of L1sub.2-Alsub.3M (M = Sc, Zr, Er, Y) was investigated based on a first-principles calculation. The point defect formation energies were firstly evaluated. ...Then, the migration energy for different diffusion paths was obtained by the climbing-image nudged elastic band (CI-NEB) method. The results showed that Al atomic and M atomic diffusions through nearest-neighbor jump (NNJ) mediated by Al vacancy (Vsub.Al) were, respectively, the preferred diffusion paths in Alsub.3M phases under both Al-rich and M-rich conditions. The other mechanisms, such as six-jump cycle (6JC) and next-nearest-neighbor jump (NNNJ), were energetically inhibited. The order of activation barriers for NNJ(Al-Vsub.Al) was Alsub.3Zr < Alsub.3Y < Alsub.3Er < Alsub.3Sc. The Alsub.3Sc phase had high stability with a high self-diffusion activation barrier, while the Alsub.3Zr and Alsub.3Y phases were relatively unstable with a low self-diffusion activation energy. Moreover, the atomic-diffusion behavior between the core and shell layers of L1sub.2-Alsub.3M was also further investigated. Zr atoms were prone to diffusion into the Alsub.3Y core layer, resulting in no stable core-shelled Alsub.3(Y,Zr), which well agreed with experimental observation.
This study utilizes desalted and denitrated treated aluminum dross (TAD) as a raw material, along with kaolin and 10 ppi (pores per inch) polyurethane foam as a template. The slurry is converted into ...an aluminum dross green body with a three-dimensional network structure using the impregnation method. A three-dimensional network aluminum dross ceramic framework (TADsub.3D) is created at a sintering temperature of 1350 °C. The liquid 5A05 aluminum alloy at a temperature of 950 °C infiltrates into the voids of TADsub.3D through pressureless infiltration, resulting in TADsub.3D/5A05Al composite material with an interpenetrating phase composite (IPC) structure. The corrosion behavior of TADsub.3D/5A05 composite material in sodium chloride solution was examined using the salt spray test (NSS) method. The study shows that the pores of the TAD3D framework, produced by sintering aluminum dross as raw material, are approximately 10 ppi. The bonding between TAD3D and 5A05Al interfaces is dense, with strong interfacial adhesion. The NSS corrosion time ranged from 24 h to 360 h, during which the composite material underwent pitting corrosion, crevice corrosion and self-healing processes. Results from Potentiodynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) indicate that, as corrosion progresses, the Esub.corr of TADsub.3D/5A05Al decreases from −0.718 V to −0.786 V, and Isub.corr decreases from 0.398 μA·cmsup.−2 to 0.141 μA·cmsup.−2. A dense oxide film forms on the surface of the composite material, increasing the anodic Tafel slope and decreasing the cathodic Tafel slope, thus slowing down the rates of cathodic and anodic reactions. Factors such as lower interface corrosion resistance or a relatively weak passivation film at the interface do not significantly diminish the corrosion resistance of TADsub.3D and 5A05Al. The corrosion resistance of the composite material initially decreases and then increases.
Applying inter-layer rolling to the wire+arc additively manufacturing (WAAM) process with increasing loads of 15kN, 30kN and 45kN, achieves excellent mechanical properties for 5087 (Al-Mg4.5-Mn) ...alloys. Compared with the as-deposited alloy, the average micro hardness, yield stress and ultimate tensile strength of 45kN rolled alloys reached to 107.2 HV, 240MPa and 344MPa, which were enhanced by 40%, 69% and 18.2%, respectively. Primary coarse grain structures were found to become greatly refined with an evident rolling texture after deformation. The strengthening mechanisms mainly are deformation strengthening, grain refinement, and solution strengthening. Meanwhile, the elongation of rolled alloys stays over 20%. The plasticity was not obviously diminished compared with the as-deposited alloy. This is two times greater than the commercial wrought Al-Mg alloy with similar composition. The excellent plasticity may be chiefly due to grain refinement, pores closure and reduction, and grain recrystallization during the WAAM re-heating process. The combination process of rolling deformation with WAAM deposition is an effective technique in refining microstructure and improving mechanical properties for AM aluminum alloys.
In the present study, we examined changes in the microstructure and mechanical properties of AlSi10Mg alloy, initially fabricated using selective laser melting (SLM) combined with a powder-bed ...system, by applying heat treatments at temperatures of either 300 or 530°C. The as-fabricated samples exhibited a characteristic microstructural morphology and {001} texture. Melt pools corresponding to the locally melted and rapidly solidified regions were found to be composed of several columnar α-Al grains surrounded by fine eutectic Si particles. A fine dislocation substructure consisting of low-angle boundaries is present within the columnar α-Al grains. At elevated temperatures, fine Si phase precipitates within the columnar α-Al phase and coarsening of the eutectic Si particles occurs. These fine Si particles inhibit grain growth in the α-Al matrix, resulting in the microstructural morphology and 001 texture observed in the heat-treated samples. The dislocation substructure disappears in the columnar α-Al grains. Furthermore, the formation of a stable intermetallic phase occurs, reaching microstructural equilibrium after long-term exposure. The as-fabricated specimen exhibits a high tensile strength of approximately 480MPa. The strength is independent of the tensile direction, that is, normal and parallel to the building direction. In contrast, the tensile ductility is found to be direction-dependent, and is therefore responsible for a fracture preferentially occurring at a melt pool boundary. The direction-dependence of the tensile ductility was not found in the specimen that had been heat-treated at 530°C. The present results provide new insights into the control of the direction-dependence of the tensile properties of AlSi10Mg alloys fabricated by SLM.
The interfacial atomic structure and misfits of Omega precipitates formed in the face-centered cubic Al in the Al-Cu-Mg-Ag alloy have been determined by combining scanning transmission electron ...microscopy (STEM) Z-contrast imaging with chemical analysis and ab initio density functional theory (DFT) calculations. Precipitates of several thicknesses formed after heat treatment at 250 degree C, starting from 0 to 2 unit cells of Omega phase, were examined by STEM in four different projections. The results show that a remarkably stable double-layered interface is formed at all observed thicknesses, which separates the Omega phase from the Al matrix. The outermost interfacial layer next to Al is composed of Ag atoms in a hexagonal structure and Mg or Cu atoms below the center of the hexagon. Structural models constructed based on the experimental data were relaxed using DFT-based molecular dynamics calculations. The results show that interfacial Mg atoms, together with Ag atoms, greatly stabilize the interface structure and consequently the Omega phase on the Al {111} habit planes. Comparison between the measured and calculated precipitate misfit along the thickness direction suggests that atomic substitutions of light atoms, Al and Mg, at the interface mediate the misfit strain and free energy, which is further supported by experimental evidence obtained from STEM. Thus, we have identified here: (i) the driving force for the Ag and Mg segregation in the formation of the Omega phase; (ii) the precipitation sequence characterized by a stable interfacial double-layer; and (iii) an interfacial substitution mechanism for misfit accommodation.
While it is generally accepted that the rupture of SLM AlSi10Mg tensile specimens occurs at the melt pool boundary, the exact zone and microstructural features responsible for the rupture have not ...been clearly identified. In this study, the microstructures and local mechanical properties at the melt pool boundary are thus analyzed in details. The Si phase fraction and the Si precipitate spacing are measured by image analysis and SEM-EDS analysis. Hardness tests are performed by nanoindentation. Fracture features are observed on broken samples. It is found that the Heat Affected Zone (HAZ) exhibits low hardness due to coarse non-coherent Si precipitates. Void nucleation occurs at the interface between the coarse Si precipitates and the Al matrix by dislocations piling up. For that reason, the HAZ is found to be the preferential region where fracture is likely to occur. This analysis is confirmed by the matching of Si precipitate spacing within the HAZ with dimple spacing observed in fracture surfaces. Moreover, a simple analytical approach of the thermal history during manufacturing, using Rosenthal's equation, allows elucidating the mechanisms by which the processing conditions affect the fracture behavior.
Display omitted
The cold metal transfer (CMT) based wire-arc additive manufacturing (WAAM) technology has been widely recognized as a suitable method for fabricating large-sized aluminum alloy components. However, ...the poor mechanical properties of the as-deposited aluminum alloys prevent their wide application in the aerospace industry. In this paper, three categories of samples with different interlayer deformation strains were fabricated by WAAM. These samples were further investigated to evaluate the effects of interlayer deformation on the mechanical properties, microstructural evolution, and the underlying strengthening mechanism. The grain size distribution and internal sub-microstructure were characterized by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). As compared to the as-deposited samples, the yield strength and ultimate tensile strength of the 50.8% deformed sample increased from 148.4 to 240.9 MPa and from 288.6 to 334.6 MPa, respectively. The microstructure of the samples with interlayer hammering exhibited highly refined grain, which is a combined result of deformation and subsequent intrinsic in-situ heat treatment induced by the next deposition layer. The recrystallized grains can be further deformed with subsequent hammering, which leads to an increase in dislocation density and contributes to an increase in ultimate tensile strength of the additively manufactured 2319 aluminum alloys with interlayer hammering.
Display omitted
The 2195 aluminum alloy has been widely utilized in the aerospace field, of which dynamic recrystallization microstructures have a substantial effect on the mechanical properties of aerospace parts. ...In this study, 2195 aluminum alloy was compressed at 300–520 °C using a Gleeble 3500-GTC thermo-mechanical testing system. The discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) behavior of 2195 aluminum alloy at medium/high temperature was studied. The results demonstrated that during medium temperatures (300–360 °C) deformation the main softening mechanism was DDRX, and at high temperatures (420–520 °C), it was CDRX. CDRX of 2195 aluminum alloy involved three types of subgrain-forming mechanisms: dislocation tangling to form subgrains, microscopic shear bands to form subgrains, and the coalescence of two small subgrains to form larger subgrains. In addition, several recrystallized grains underwent geometric dynamic recrystallization (GDRX) at high temperature and extensive deformation (480 °C-80% or 520 °C-60%).
•DDRX occurred in 2195 aluminum alloy at medium temperature.•CDRX occurred in the alloy at high temperature.•Continuous dynamic recrystallization is based on 3 subgrain forming mechanisms.•GDRX occurs during large deformation at high temperatures for 2195 aluminum alloy.
The effect of Zr content of SLM processed (SLMed) Zr modified Al-4.24Cu-1.97Mg-0.56Mn alloys on the formability, microstructure and mechanical properties has been investigated. It is observed that, ...with the addition of Zr increaseing, the tendency of density is consistence with the tendency of thermal conductivity and solidification temperature range (STR). The addition of Zr promotes the expansion of processing window as well as the transformation of grain type from columnar to equiaxed. Al3Zr and ZrO particles act as heterogenous nucleation for solidification processing, resulting in a very fine microstructure, low cracking sensitivity and good performance. The alloy tailored by adding 2 wt% Zr showed the maximum processing window and ultimate tensile strength (UTS = 493.3 MPa). The effect of Al3Zr on grain refinement, inhibition of cracks and improvement of mechanical properties have been discussed.
Display omitted
•Processing windows of Al-4.24Cu-1.97Mg-0.56Mn alloys modified with different Zr contents.•The effect of Zr addition on the solidification cracking and cracking control mechanism.•The effect of Zr addition on the grain refinement mechanism and the control of mechanical properties.
PDF
