In order to evaluate the corrosion performance of polyurethane-ZnO/Zn coatings for LY12 aluminium alloy sheets in 3.5 % NaCl solution. Firstly, the composite coatings were prepared and the optimum ...stick-fill ratio was obtained. Secondly, the corrosion characteristics were characterised by SEM, EDS and electrochemistry for different immersion times and the electrochemical behaviour was investigated by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and kinetic potential polarisation curves (PP). The results show that the coating with a viscosity-fill ratio of 1:4 has a uniform distribution, the corrosion potential Ecorr is more positive, the corrosion current density icorr is the smallest, |Z|0.01Hz maintains the highest, and the coating has a good anti-corrosion performance. After soaking in 3.5 % NaCl solution for 20 days, the coating reaction resistance increased from 1.71 × 104 Ωcm2 to 6.59 × 1017 Ωcm2, and the self-corrosion current decreased from 5.12 × 10−5 A/cm2 to 5.01 × 10−7 A/cm2, indicating that the corrosion resistance of LY12 aluminium alloy sheet in the solution increased.
•1. Prepare high solid content polyurethane anti-corrosion coatings using polyurethane, ZnO and Zn as raw materials.•2. Change the ratio of polyurethane to ZnO/Zn to obtain the optimal adhesive filling ratio for anti-corrosion coatings.•3. The corrosion behaviour of LY12 aluminum alloy sheets with the best adhesive to filler ratio coating was studied.
Laser Shock Peening is a fatigue enhancement treatment using laser energy to induce compressive Residual Stresses (RS) in the outer layers of metallic components. This work describes the variations ...of introduced RS‐field with peen size and coverage for thin metal samples treated with under‐water‐LSP. The specimens under investigation were of aluminium alloy AA2024‐T351, AA2139‐T3, AA7050‐T76 and AA7075‐T6, with thickness 1.9 mm. The RS were measured by using Hole Drilling with Electronic Speckle Pattern Interferometry and X‐ray Diffraction. Of particular interest are the effects of the above mentioned parameters on the zero‐depth value, which gives indication of the amount of RS through the thickness, and on the value of the surface compressive stresses, which indicates the magnitude of induced stresses. A 2D‐axisymmetrical Finite Element model was created for a preliminary estimation of the stress field trend. From experimental results, correlated with numerical and analytical analysis, the following conclusions can be drawn: increasing the spot size the zero‐depth value increases with no significant change of the maximum compressive stress; the increase of coverage leads to significant increase of the compressive stress; thin samples of Al‐alloy with low Hugoniot Elastic Limit (HEL) reveal deeper compression field than alloy with higher HEL value.
In the present study, aluminium metal matrix composites (AMCs) were successfully produced through stir-squeeze casting using a novel approach. The feasibility of using car scrap aluminium alloy ...wheels (SAAWs) as the matrix material and spent alumina catalyst (SAC) from oil refineries as reinforcement material was investigated. For the purpose of comparision, composites were also produced using AlSi7Mg (LM25 grade) aluminium alloy as a matrix and alumina as reinforcement particles through the stir-squeeze casting process. In total, four different combinations of composites (AlSi7Mg + alumina; scrap aluminium alloy + alumina; AlSi7Mg + spent alumina catalyst; scrap aluminium alloy + spent alumina catalyst) were produced and characterized. Microstructural investigations using an optical microscope and a scanning electron microscope (SEM) as well as energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) revealed that in all four composites the reinforcement formed a mixture in the eutectic silicon phase of the matrix alloy. The alumina particles' size and content ratio greatly influenced this mixture's formation and morphology. The composites produced using alumina exhibited smaller pore sizes and lower porosity as compared to the composites produced with a spent alumina catalyst. Superior mechanical properties were also obtained when using alumina as reinforcement, and better mechanical properties can mainly be attributed to the morphology of the reinforcement and silicon eutectic phase mixture. The scrap aluminium alloy + alumina exhibited the lowest porosity (7.3%) and abrasive wear loss (0.11 mg for the finest abrasive), highest hardness (58.5 BHN), and second highest ultimate tensile strength (UTS) (125 MPa) and ultimate compressive strength (UCS) (312 MPa) among the four composites.
Display omitted
•A novel approach used to produce metal matrix composites from waste materials.•The alumina reinforcement combines with the eutectic silicon to form a mixture.•Acicular, blunted, needle-like mixture morphology improves mechanical properties.•Enhanced ultimate tensile (125 MPa) and compressive strength (312 MPa) obtained.
A method to eliminate hot cracking phenomena for aluminium alloys in Laser Beam Melting (LBM) is presented in this paper, focused here on the 6061 alloy. 6061 is a precipitation-hardened aluminium ...alloy, containing magnesium and silicon as its major alloying elements. This alloy, commonly used in the aeronautic and automotive industries, thanks to its excellent weight to strength ratio and high thermal conductivity, is particularly prone to hot cracking, in particular during LBM processing. The solution to remove cracks proposed in the present paper is to induce grain refinement to avoid the development of large columnar structures. To this end, various quantities of Yttrium Stabilized Zirconia (YSZ) are added to an Al6061 base powder using a dry mixing (TurbulaⓇ) procedure. Experiments highlight a grain refinement effect depending on the added YSZ quantity. From 1 vol% on, SEM and EBSD images reveal an equiaxed-columnar bimodal grain microstructure. Results show that the addition of 2 vol% YSZ allows to fully avoid cracks due to a continuous equiaxed band at melt pool boudaries. Additionally, TEM and DRX investigations provide new insights into the becoming of added particles along the printing process. The experimental results are then discussed on the basis of a number of existing solidification models, with a focus on the necessary conditions for the establishment of an equiaxed solidification regime.
Display omitted
The aim of this work is to develop a new class of aluminium alloy matrix composites (AAMCs) reinforced with different weight percentages of zirconium diboride (ZrB2) particles through the bottom ...pouring type stir casting process. The mechanical and corrosion behaviours of aluminium can be improved by the addition of ceramic particles. Mechanical behaviours and microstructure of the composites were studied. Homogeneous distribution of ZrB2 particles in the matrix was analysed using scanning electron microscope. The corrosion behaviour of the proposed composites was analysed by electrochemical assessments, such as polarization tests and AC impedance spectra. Prepared specimens are submerged inside aqueous sodium chloride (NaCl: 3.5%) solution. Corrosion potential, current, resistance of linear polarization, capacitance of double layer, resistance of charge transfer and resistance of corrosion in material were determined. From corrosion outcomes, we concluded that AA7178–ZrB2 metal matrix composite revealed higher corrosion resistance than AA7178. The rate of corrosion resistance, hardness, impact strength and tensile strength was augmented gradually by way of increasing weight per cent of ZrB2 particles in the AA7178 matrix. Hardness was improved by 26% and the ultimate tensile strength was improved by 15% for the inclusion of 10 wt% ZrB2 particles in the AA7178 matrix.
•Aluminium alloy matrix composites reinforced with zirconium diboride particles were developed by stir casting process.•Mechanical, corrosion behaviours and microstructure of the composites were studied.•Homogeneous distribution of ZrB2 particles in aluminium alloy matrix was observed from scanning electron microscope.•AA7178–ZrB2 metal matrix composite revealed higher corrosion resistance than aluminium alloy.•Hardness and ultimate tensile strength was improved for the inclusion of ZrB2 particles in AA7178 matrix.
We used X-ray computed tomography (CT), microscopy and hardness measurements to study Al–Si10–Mg produced by selective laser melting (SLM). Specimens were subject to a series of heat treatments ...including annealing and precipitation hardening. The specimen interiors were imaged with X-ray CT, allowing the non-destructive quantification and characterisation of pores, including their spatial distribution. The specimens had porosities less than 0.1%, but included some pores with effective cross-sectional diameters up to 260μm. The largest pores were highly anisotropic, being flat and lying in the plane normal to the build direction. Annealing cycles caused significant coarsening of the microstructure and a reduction of the hardness from (114±3) HV, in the as-built state, to (45±1) HV, while precipitation hardening increased this to a final hardness of (59±1) HV. The pore size and shape distributions were unaffected by the heat treatments. We demonstrate the applicability of CT measurements and quantitative defect analysis for the purposes of SLM process monitoring and refinement.
Display omitted
•We examined SLM Al–Si10–Mg with X-ray CT, microscopy and hardness measurements.•The size, shape and position distributions of the internal pores were determined.•Heat treatments alter the microstructure and hardness, but the pores are unaffected.•The largest pores are highly anisotropic, being at or disc-like in the xy plane.•CT and statistical analysis can play a role in improving the manufacturing process.
In this work, the corrosion mechanism of AA2024-T3 covered by a lithium-based conversion layer is studied with high spatial and temporal resolution. Although the aluminium alloy surface is protected ...by a multi-layered conversion layer, areas around intermetallic phases (IMPs) represent weak spots due to an insufficient generation of a protective inner dense layer. For the freshly formed conversion layer, both the top and the inner layer undergo a gradual dissolution upon exposure to relatively dilute NaCl solution within 2 h due to their chemical instability. For the ambiently-aged conversion layer, most corrosion activity around IMPs is related to the S-phase and large constituent phases, due to their active nature and the lower local conversion layer quality, respectively. Moreover, S-phase-related corrosion activity lasts approximately 8 h due to fast dissolution whereas reactions induced by large constituent particles remain active over the entire re-immersion period of 12 h.
Display omitted
•SECM and EN were used to study the corrosion of Li-based conversion layer covered AA2024-T3.•The structure of the freshly-formed Li-based conversion layer is unstable upon re-immersion.•The S- and large constituent phases are more prone to corrosion attack in re-immersion tests.•The S-phase exhibits relatively high corrosion kinetics and early undercutting from the matrix.
Selective Laser Melting (SLM) has received tremendous attentions due to its high degree of flexibility for the design and fabrication of geometrically complex parts. However, the majority of the ...currently applied metals for this advanced technology are still based on the traditional weldable and/or castable alloys, and the resulting mechanical properties of SLM fabricated samples are often mediocre. This is because the conventional alloys are not designed to accommodate the dynamic metallurgical characteristics of the SLM process and the benefits offered by SLM are not fully captured. In this study, an experimentally-based novel alloy development methodology utilising wedge mould casting and laser remelting is proposed, and the processability and properties of the developed alloys can be predicted for SLM. By mimicking the high solidification rate of the SLM process, unconventionally large amounts of solute were successfully placed into solution in the aluminium (Al) matrix. A high strength Al-Mn-Sc based alloy has been successfully developed and verified by SLM processing. The developed alloy possessed an average yield strength of about 430 MPa and a ductility of 21% in the as fabricated state, compared to approximately 570 MPa and 18% after direct ageing for 5 h at 300 °C, respectively.
Display omitted
•An experimental-based high strength aluminium alloy development methodology has been proposed.•High strength Al-Mn-Sc based alloys have been successfully developed specifically for SLM.•SLM fabricated Al-Mn-Sc alloy possessed a high yield strength of 570 MP a direct post-ageing treatment (300 °C for 5h).
•Textures on Ti6Al4V and AA2024-T3 has been produced by ultra-short laser-material.•Pulse energy between 1 and 20 µJ and number of pulses per impact from 10 to 200.•For numbers of pulses <10, the ...treatment is superficial with limited ablation depth.•Dimples with an appreciable depth produced by blind drilling with number pulse >50.•The effective penetration depth of laser was greater for 2024-T3 than for Ti6Al4V.
Laser texturing can be used for surface modification of metallic alloys in order to improve their properties under service conditions. The generation of textures is determined by the relationship between the laser processing parameters and the physicochemical properties of the alloy to be modified. In the present work the basic mechanism of dimple generation is studied in two alloys of technological interest, titanium alloy Ti6Al4V and aluminium alloy AA2024-T3.
Laser treatment was performed using a pulsed solid state Nd: Vanadate (Nd: YVO4) laser with a pulse duration of 10 ps, operating at a wavelength of 1064 nm and 5 kHz repetition rate. Dimpled surface geometries were generated through ultrafast laser ablation while varying pulse energy between 1 µJ and 20 µJ/pulse and with pulse numbers from 10 to 200 pulses per spot. In addition, the generation of Laser Induced Periodic Surface Structures (LIPSS) nanostructures in both alloys, as well as the formation of random nanostructures in the impact zones are discussed.
Micro arc oxidation (MAO) coatings were prepared on the surface of 2195 Al-Li alloy by adding different amounts of indium sulphate (In
2
(SO
4
)
3
) into an electrolyte consisting of silicate and ...phosphate. The surface, cross section, phase composition, and electrochemical experiments of MAO coatings were analysed. X-ray diffraction results show that the coating was composed of γ-Al
2
O
3
, α-Al
2
O
3
, and In
2
O
3
. The results show that after adding In
2
(SO
4
)
3
, the discharge holes on the surface of the coating were more uniform and the thickness was also increased. The corrosion resistance of MAO coatings was improved by the addition of In
2
(SO
4
)
3
.
PDF
