Al-Zn Alloys Research Articles

Manipulating scanning strategies towards controlled microstructure of laser remelted Mg–3Al–1Zn alloy

Various laser scanning strategies of multitrack products, consisting of a default Raster pattern (R1), a Raster pattern with a changed line order (R2), and a default Zigzag pattern (Z1), with different overlap rates ranged from 0.7 to 0.5, have been conducted to investigate microstructure evolution for Mg–3Al–1Zn alloy. As the overlap rate changes from 0.7 to 0.5, the average grain size decreases and the texture is slightly concentrated, except for R2 pattern. For effect of different scanning pattern, a relatively small average grain size can be obtained using the R1, R2 patterns compared to using the Z1 pattern; a relatively weak texture can be obtained using the R1, Z1 patterns compared to using the R2 pattern. The utilization of Z1 pattern results in a further texture weakening compared to that of the R1 pattern. Microstructure evolution of scanning strategy is mainly determined by low-undercooling-required epitaxial growth along temperature gradient directions at the solid/liquid interface. Combined with computational thermal-fluid dynamics simulation, a strong fluid flow within the molten pool promotes side expansion of the molten pool, resulting in the larger overlap area, the corresponding three-times remelting domain and continuous deflections of grain major axes.

Microstructural and mechanical analysis of heat-treated Zn-Al alloy and Zn-Al/ZrB2 composites

This study explores the impact of heat treatment on Zn-Al alloy and Zn-Al/ZrB2 composites. Specifically, heat treatment at 250 °C for 3 h resulted in a significant refinement of grain structure and notable hardness improvement, showcasing an optimal combination of microstructural and mechanical properties. However, higher temperatures led to increased grain size and reduced hardness for both alloy and composites. These findings offer promising insights for optimizing processing parameters, enhancing the performance of Zn-Al based composites in critical engineering applications.

Fatigue Behavior and Fracture Surface Analysis of Corroded High-Strength Bridge Cable Wires.

Bridge cable wires suffer from alternating stress and environmental erosion, leading to premature failure prior to its design life. This paper investigates the fatigue and mechanical behaviors of corroded bridge cable wires with a zinc-aluminum (Zn-Al) alloy coating. Based on the salt spray corrosion test and microstructure analysis, the anti-corrosion resistance and corrosion appearance characteristics of the Zn-Al alloy coating and galvanized coating were investigated. The Zn-Al alloy coating was superior in resistance to corrosion fatigue for the improvement in toughness and the generation of anti-corrosion Zn-Al and Fe-Zn-Al phases. Equations of the accelerated corrosion depth of the steel wires had been regressed to roughly estimate the corrosion life of the Zn-Al alloy coating, which can reach 29.1 years with a thickness of 70 μm. The fatigue and mechanical properties of the bare wires after the salt spray test were further studied based on tensile tests and fatigue tests. The fatigue properties of the bridge cable wire would decrease with the corrosion degree due to the deterioration and embrittlement of materials, where ductility characterized by the elongation rate was the most affected. Fracture surfaces of the wires were captured and analyzed based on a method for recognizing graphical contours. Insufficient fatigue life may occur in the steel wires after corrosion and increase with the degree of corrosion. The pit depth logarithmically weakened the fatigue life of steel wires for the weakening of fatigue toughness and the bearing area. The flat fracture was more common with a single fatigue source, while multiple fatigue sources led to step-like fractures for the generation of multiple dispersed crack propagation regions. Corrosion fatigue was more sensitive to the existence of fatigue sources than the reduction. Multiple initiation sources significantly reduced the fatigue life due to the cracking facilitation of the joint effect of multiple pits. The electrochemical reactions of corrosion can lead to material embrittlement and a reducing effect on the fracture toughness of the steel wires.

Effects of Al content on microstructure and corrosion behavior of Zn-Al alloy coatings

Alloying Zn with other metals is an alternative method to create advanced alloys with better corrosion properties, in this work the electrodeposition of Zn-Al binary alloy in sulphate-based acidic bath and with different Al2O12S3 content from 0.03 to 0.1M on a treated copper substrates was studied, the structure and microstructure of the coatings were analysed by X-ray diffraction (XRD) and scanning electron microscope (SEM) supported by (EDX) analysis, the microhardness was measured, the corrosion resistance was evaluated by potentiodynamic polarization (Tafel), the effect of Al ions was visible on the structure, (XRD) spectra showed zinc phase (η-phase), and Al phase (α-Al phase) with Al peak intensity increasing along with the increase of Al concentration, the microhardness also enhanced gradually to 252.33 HV, the corrosion current density decreased by almost 13 times and the corrosion resistance was drastically improved at 0.1M Al.

Dually boosting the performance of photovoltaic module via integrating elastocaloric cooler

Photovoltaic module (PVM) only can utilize visible and ultra-violet parts of solar spectrum, constrained by the Shockley-Queisser limit. To fully use solar spectrum, in this study, solar selective absorber (SSA) and elastocaloric cooler (ECC) are gradually hybridized with PVM to form a new hybrid system for the first time. The performance metrics of PVM, ECC, and hybrid system, taking into account various irreversible effects, are mathematically derived. The hybrid system achieves approximately a 63% enhancement in both energy efficiency and power output density compared to a standalone PVM, outperforming other similar PVM-based hybrid systems. Exhaustive parametric studies show that increasing the operating temperature, solar irradiance, diode ideality factor, length ratio or section area ratio can enhance the hybrid system performance. The optimal combination of refrigerant and actuator materials are, respectively, Ni–Ti and Cu–Zn–Al alloys. Furthermore, a case study conducted to forecast practical performance under southeast China's weather conditions reveals that the hybrid system attains significant annual maximum energy efficiency and power output density, reaching 29.3% and 54.66 W m−2, respectively. The findings from this study provide valuable insights and recommendations for the optimum design and operation for such a hybrid system.

Extrusion limit diagram of Mg–5Bi–3Al–1Zn alloy and effects of extrusion parameters on its microstructures and mechanical properties

Hot-compressive tests and finite element simulations were carried out to construct an extrusion limit diagram of a Mg–5Bi–3Al–1Zn (wt.%) alloy in this work. It was observed that 310 °C became a dividing line, below which the safe extrusion zone was narrow because the stress required to induce the plastic flow of alloy was higher than the pressure limit. Once the temperature exceeded this critical temperature, a wide safe extrusion zone controlled by the cracking limit was attained. The theoretical maximum ram extrusion speed was calculated as approximately 48 mm/s at 310 °C. No hot cracks occurred on the surface of alloys extruded at 30 and 44 mm/s; while at 56 mm/s, obvious orange peel defects were observed. Through further microstructural observation, the 44 mm/s extruded alloy exhibited a complete dynamic recrystallization structure with an average grain size of 21.9 μm, along with a relatively weak basal fiber texture (with a maximum pole intensity of 5.8) and plentiful nano-Mg3Bi2 phases. These microstructure features led to superior tensile properties (namely a tensile yield strength of 270 MPa, an ultimate tensile strength of 375 MPa and an elongation of 15%) at the high-speed extrusion.

New kink-band formation mechanism discovered in Zn-Al alloy with mille-feuille microstructure

The discovery of kink-band strengthening in some Mg-alloys has focused attention on the development of mille-feuille-structured alloys composed of alternating stacks of plate-like soft and hard phases. In this study, we focused on the Zn-6.0mass%Al alloy that is composed of hcp-Zn and fcc-Al, and is used as a coating material on hot-dip galvanized steel sheet for automobile. The deformation behavior was examined by using directionally solidified crystal. As expected, kink bands formed in alloys but two different kink-band formation mechanisms were identified. One is a classical mechanism which involves the formation of an array of dislocations perpendicularly aligned with their slip planes. The other is a new mechanism which has never been reported in any materials before, and a prior {11 2¯ 2} pyramidal slip in the Zn matrix phase acts as the source, with dissociation of the <112¯3¯> dislocation supplying the <11 2¯ 0> dislocation for kink-band formation. The latter newly found mechanism introduces fine kink bands uniformly into the specimen, which effectively causes kink-band strengthening during subsequent deformation compared to kink bands introduced by conventional formation mechanism. This study provides a new strategy for enhancing kink-band strengthening in alloys by the control of the morphology of kink bands.

Eco-Friendly Electrodeposition of Al-Zn Alloy from AlCl3-Urea Deep Eutectic Solvent

The electrodeposition of Al-Zn alloy from an aluminium chloride-urea (AlCl3-urea) deep eutectic solvent (DES) containing 0.1 M ZnCl2 near room temperature was investigated. Cyclic voltammetry demonstrates that Al and Zn can be co-deposited, but the presence of Zn(II) restrains the reduction of Al(III). Linear sweep voltammetry reveals that increasing temperature facilitates the reduction of Zn(II) and Al(III), but the promotion effect on the Zn(II) reduction is greater than that on Al(III) reduction. Chronoamperometry analysis indicates that the electrocrystallization of Al-Zn alloy on a glassy carbon electrode follows instantaneous nucleation, which is similar to that of pure Al. SEM shows that the obtained alloy coating is smooth but not compact. With the increase of temperature, the content of Zn in deposits increases, the grain grows up and the microstructure transforms from granular to cluster structure. EDS and XRD analyzes prove that the deposits are pure Al-Zn alloy and composed of α phase and η phase. Tafel polarization test confirms the as-prepared alloy coating with higher Zn content (45 wt%) possesses excellent corrosion resistance. All these findings promise an eco-friendly and simple route to produce the Al-Zn alloy coating with excellent corrosion resistance near room temperature.

Formation, control and functionalization of nanoporous zinc by selective corrosion of Al–Zn alloys with varying compositions

Nanoporous zinc with a bicontinuous ligament/channel structure has abundant active sites and fast charge transfer behavior, leading to efficient conversion of CO2 to CO.

Cooling Effect on Nano Eutectoid Phase Formation of Hypereutectic Zn-Al Alloy

To understand the nano phase formation, cooling experiments of a hypereutectic Zn-Al alloy containing 6 wt% of Al are carried out under two different cooling rates of 0.04 and 10.00 °C/s. The applied cooling rates significantly influence the phase change behavior of the investigated alloy. The liquidus temperature (TN) for the nucleation of the primary phase decreases from 390.3 to 382.9 °C, and the undercooling increases from 0.7 to 8.1 °C, as the cooling rate rises from 0.04 to 10 °C/s. The eutectic and eutectoid temperatures decrease from 381.5, 277.7 to 375.6 and 267.6 °C, respectively, when the cooling rate increases from 0.04 to 10.00 °C/s. The SEM and EDS analyses reveal that the solidified alloy contains the primary γ-ZnAl phase, the eutectic β-Zn phase, and the eutectoid α-Al and eutectoid β-Zn phases. The fast phase change and transformation caused by rapid cooling results in the formation of nano eutectoid phases and fine microstructure.

Dispersion of stable quasicrystal phase by precipitation during extrusion in a Mg–Zn–Al alloy: Microstructure and mechanical properties

Precipitation of stable icosahedral quasicrystalline phase (i) has been recently reported in a Mg6Zn3Al (in wt%, ZA63) alloy on ageing after solutionizing treatment of cast alloy to dissolve dendritic i-phase. This offers an opportunity to disperse this phase in a ZA alloy through a solutionizing treatment followed by extrusion, thereby precipitating the i-phaseduring extrusion. By this process, the i-phasecan be dispersed in the alloy uniformly, instead of dispersion from the cast structure by extrusion. In this study, a cast ingot of ZA63 alloy was solutionized at 400 ∘C, followed by extrusions at 255 ∘C and 300 ∘C. Extrusion at 255 ∘C resulted in larger amount of i-phaseprecipitation (about 4.5 mass%), in which spherical precipitates of size about 100 nm or less were distributed in the matrix and boundaries of grains of average size 2.4 ± 1.0μm, exhibiting true yield strengths of 263.7±1.4MPa in tension and 255.4±5.0MPa in compression (with elongation to failure of about 18% in both cases). Extrusion at the higher temperature of 300 ∘C resulted in fewer precipitates (about 1.4 mass%) and larger average grain size of 12.9 ± 6.1μm and i-phaseprecipitates of size 500 nm which were mostly at the grain boundaries, and consequently lower true yield strengths of 214.4±1.3MPa in tension and 159.3±0.3MPa in compression. The strength after extrusion at 300 ∘C increased by 48 MPa in tension and 38 MPa in compression on ageing at 250 ∘C for 20 min. Ageing precipitate phases were identified to be i-phase, Mg4Zn7 and possibly ternary ϕ-phase. Phase equilibrium and change in morphology of phases during ageing has been discussed. The peculiar nature of work hardening during tensile deformation has also been discussed.

Revealing the influence of solution and pre-deformation treatment on the corrosion resistance of Y-modified AZ91 magnesium alloy for lithium-ion battery shell

The usage of Mg–Al–Zn alloys for lithium-ion battery shell is able to achieve further lightweight of electric vehicles, and their corrosion resistance would highly determine the service life. In this work, therefore, a Y-modified AZ91 magnesium alloy (AZ91-0.5Y) was first prepared by conventional casting and following hot extrusion, and the influence of solution treatment (ST) and subsequent pre-deformation (SP) treatments on its electrochemical corrosion and stress corrosion cracking (SCC) resistance in 1 mol/L LiPF6 electrolyte were then investigated. The results indicated that the presence of large lamellar or rod-like β-Mg17Al12 phase in as-extruded AZ91-0.5Y alloy would lead to serious micro-galvanic corrosion and SCC. After solution treatment, the β-Mg17Al12 phase almost completely dissolved into Mg matrix, weakening the micro-galvanic corrosion and anodic dissolution (AD) and hydrogen embrittlement (HE) effect. Further, the subsequent pre-deformation treatment could introduce dislocation, more precipitation of Al2Y phase, massive twins and optimized texture, leading to the improved corrosion resistance and mechanical strength as well as the formation of well-integrated protective corrosion product film MgF2 with low porosity. As a result, the corrosion and SCC resistance of as-extruded, ST and SP specimens is ordered from low to high.

Mechanical alloying and phase transition of immiscible Al/Zn system during high-pressure torsion

Two half-disk samples of pure Al and pure Zn were mechanically alloyed via high-pressure torsion (HPT) processing, followed by post-deformation annealing (PDA). The microstructure evolution of the Al–Zn alloy was studied by scanning electron microscopy, transmission electron microscopy and molecular dynamics (MD) simulations. The results indicated that the HPT-processed Al/Zn assembly was presented as a mixture of nanocrystalline and amorphous phases. The deformation-induced special orientation of (0001)Al//(111)Zn facilitated the interatomic diffusion, and the dislocation density reached 2.17×1017 m−2 under the pinning effect of high solid solubility. Nanocrystalline, high diffusion degree, and high local dislocation density may primarily accounted for the crystalline-to-amorphous transformation in Al–Zn alloy. Moreover, the results indicated a bimodal grain size distribution of 150–250 nm and 500–900 nm, and Zn atoms were enriched at the grain boundaries, upon subsequent PDA. Under the effect of this special heterogeneous microstructure, the prepared alloy exhibited an excellent plasticity with 160% of tensile elongation.

Study of hot tensile deformation behavior and microstructure characteristics of Zn-22Al microtubes using direct resistance heating-assisted tensile tests

To explore the deformation behavior of Zn-22Al alloy microtubes during hot forming processes with rapid heating, direct resistance heating (RH)-assisted tensile tests using microtubes are introduced based on their quick and easy temperature control. Notably, the large temperature difference of the sample during the RH-assisted tensile tests affected the accuracy of the tensile test results. To perform the RH-assisted tensile tests of the microtubes correctly, the specimens were designed with optimized structures of effective and total lengths of 30 and 60 mm, respectively. Better ductility was observed in the microtube drawn at 200 °C owing to the highly activated grain boundary sliding (GBS) caused by its uniform finer grain structure, greater high-angle grain boundary (HAGB) densities in the close-to-fracture area, and intergranular ductile fracture mode. The primary deformation mechanism of the microtube during hot forming was built based on hot tensile behavior, microstructure, and fracture surface analysis. It was also demonstrated that there is an intrinsic relationship between the temperature distribution, change in the microstructure of different parts, and multiple necking phenomena of the microtube formation process.

Experimental study on the effects of three alloying elements on the mechanical, corrosion and microstructural properties of aluminum alloys

Aluminum is widely used in industries such as automobile and aerospace due to its lightweight, but its pure form lacks sufficient strength and the properties of aluminum can be modified by adding alloying elements. This paper presents the effect of adding Magnesium (Mg), Copper (Cu), and Zinc (Zn) on the mechanical, microstructural, heat treatment properties, and corrosion behavior of aluminum-based alloys. The aluminum-based alloys were manufactured with varying percentages (1 %, 3 %, 5 %, 8 %, and 10 %) of the three alloying elements using sand casting. Tension, compression, Brinell hardness, and corrosion tests were conducted to examine the effect of these alloying elements on the alloys' properties. The tensile strength is improved significantly with the increase in alloying elements for all alloys but the compressive strength and hardness are improved for Al–Cu alloy only. After heat treatment, the hardness of Al–Mg alloy increased at 8 % and 10 % Mg content while the hardness of Al–Cu alloy decreased after heat treatment for all concentrations of Cu. The hardness of Al–Zn alloys remained unaffected by the heat treatment process. The corrosion rate is minimum for Al–Mg and it is maximum for Al–Cu alloys but at 10 % concentrations, the corrosion rate of Al–Mg alloy is higher than Al–Cu alloy. The microstructural observation before and after heat treatment revealed that the grain refinement occurred for Al–Mg and Al–Cu alloys but the microstructure remained unaffected for Al–Zn alloys. The outcomes of this study offer valuable insights into customizing the mechanical characteristics of aluminum-based alloys to suit particular applications.

An insight into mechanical response and twinning behavior of bimodal textured AZ31 magnesium alloy under quasi-static and high strain rate compression

In this work, the dynamic, quasi-static response and twinning behavior of bimodal textured Mg–3Al–1Zn alloy is comparatively investigated at room temperature. The relationship between yield stress and bimodal texture is quantified and characterized as an increase of the yield stress with the increasing of the percentage of <0002>⊥ED (extrusion direction) component; the ultimate strength under high strain rate (103 s−1) was quite higher than that under quasi-static condition (10−3 s−1); but, the yield stress was just the reverse. The competition between twin nucleation and growth is significantly affected by a coupled effect of strain rate and texture. Twin nucleation shows positive strain rate sensitivity and is largely enhanced by dynamic deformation. However, the twin growth tendency is bimodal texture and strain rate dependent: it is favorable under quasi-static condition for samples with more soft orientations, while for samples with more hard orientations, dynamic deformation promotes twin growth. It is also found that a higher strain rate can stimulate the activation of more twin variant types in bimodal textured magnesium alloys.

Effect of transverse gradient extrusion process on texture and mechanical properties of Mg–3Al–1Zn alloy sheets

Transverse gradient extrusion (TGE) processes with different die inclined angles of 15°, 30°, 45°and 60° were used to produce Mg–3Al–1Zn sheets, thereby tailoring texture and mechanical properties of Mg alloy sheets. Microstructure, deformation texture and final mechanical properties of the obtained sheets were detected and discussed. Furthermore, the rheological behavior of Mg alloys during extrusion was analyzed by finite element method. As the TGE die inclined angle changed, the flow velocity along the transverse direction (TD) and effective strain difference along extrusion direction (ED) were changed during extrusion, and therefore the microstructure and texture of extruded sheets are altered. With increase of TGE die inclined angles, fine grain size and uniform microstructure were obtained. The base poles of most grains for the extruded sheets gradually deviate from normal direction (ND) to ED at center region and inclined from ED to TD at 1/4 edge region. A large elongation of 33.9 % and a low yield stress of 125 MPa can be obtained in the TGE-45 sheet.

Investigation of the microstructure and mechanical properties of Mg–Al–Zn alloy joints formed by different laser welding processes

Abstract The microstructure and mechanical properties of Mg–Al–Zn alloy joints by using autogenous laser beam welding (LBW) and laser-MIG hybrid welding, respectively, are investigated. The results show that the weld formation of the hybrid welding joint is relatively good, and there are mainly α-Mg matrix phases and β-Mg17Al12 strengthening phases in the weld metal. The microstructure in the fusion zone (FZ) of the two joints is different. The LBW joint is composed of columnar crystal and equiaxed dendrite. The hybrid welding joint consists of fine equiaxed grains, and the grain size in the laser zone is larger than that in the arc zone. The microhardness in FZ is higher due to the precipitation of the β-Mg17Al12 phase in this region. Under the optimized welding procedure, the strength coefficient of the two joints is &gt;90%. There are many dimples on the tensile fracture surface of the hybrid welding joint, which is characterized by the pattern of the ductile fracture.

THERMOPHYSICAL PROPERTIES OF DOPED RARE-EARTH METAL ALLOY ZN55AL

The paper presents the results of a study of the thermophysical properties of Zn55Al alloy doped with scandium, yttrium, cerium, praseodymium, neodymium and europium in a wide temperature range. It was established that in all studied samples anomalous cooling associated with a first-order phase transition is observed. It is assumed that the two observed cooling processes of the alloy are associated with radiative and convective heat transfer. It was revealed that the radiation process ends quickly and the sample is subsequently cooled only due to convective heat exchange with the environment. Using data on the temperature dependence of the heat capacity of aluminum and zinc, the temperature dependences of the heat capacity of the Zn55Al alloy and its heat transfer coefficient were calculated using the Neumann- Kopp rule . The results obtained show that the temperature dependence of the heat capacity is described by the polynomial С(Т)=a + b T + c T2 + d T3. It has been shown that the heat capacity of alloyed alloys is less than that of the original alloy and increases with increasing temperature, and changes differently with increasing concentration of the alloyed metal. For Zn55Al alloys alloyed with europium, cerium and neodymium, the heat capacity decreases with increasing concentration, and for alloys alloyed with praseodymium and scandium it increases. The phase transition process is observed in the Zn55Al alloy and becomes more pronounced upon alloying, which is explained by the process of monotectoid transformation α1→α2+β at a temperature of 529 K. It is shown that the results obtained are consistent with the zinc-aluminum phase diagram.

A Study of Crevice Corrosion Susceptibility of Zn-Al Alloys in a High-pH Environment

This paper aims to clarify the effect of polymer coating damage of dual polymer–zinc coating used to protect rebar reinforcement from corrosion. The coating damage can result in crevices between the two materials. At these crevices, corrosion–passivation plays an important role in the integrity of the intended coating and the protectiveness of the steel base metal. An experimental design was developed to replicate a crevice of Zn-2%Al alloy. This alloy is commonly used for the dual coating protection of rebars. Experiments in this investigation were performed to test several crevice sizes and conditions to assess the state of crevice corrosion. Prepared electrodes were submerged in a 1 M NaOH solution and connected to a data logger to monitor the potential. A special reference electrode was prepared using activated titanium, against which the potential was measured. Additionally, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were carried out to assess the corrosion rate of the different specimens. The results suggest that, in the absence of a crevice, corrosion occurred on bare specimens. However, whenever a crevice was present, a shift in potential and corrosion rate values indicated that the specimen shifted from an active corrosion regime to a passive one. This shift (gain) in potential was measured as approximately 0.9 V, resulting in a shift in the electrode potential to −0.6 V (SCE). The analysis showed that the solution inside the crevice shifted toward lower pH values, with pH = 12 suggested as the level that supports more passivity inside the crevice according to the Pourbaix diagram.