Zn Grains Research Articles

Significantly improved corrosion resistance of Zn layer coated Mg alloy prepared by friction stir processing

Mg-2Zn-0.46Y-0.5Nd alloy coated with pure Zn layer of about 750 μm was prepared by friction stir processing technique. The Zn layer was strongly bonded with the Mg alloy substrate and no intermetallic compounds were found at the Zn/Mg alloy interface. In the center of the coated Zn layer, a bonded structure consisting of coarse Zn and fine Mg alloy grains were formed due to the flowing of the materials from the lower to the upper plate. The electrochemical tests in 3.5% NaCl solution showed that the corrosion current density of Zn layer coated FSPed Mg alloy was only about 2.41 × 10−6 A/cm2, significantly lower than 2.01 × 10−5 A/cm2 of the uncoated FSPed Mg alloy. In addition, the FSPed Mg alloy with Zn layer showed uniform surface morphology after corrosion tests, which was very different from the severe pitting corrosion of the uncoated counterpart.

Two-dimensional phase-field study for spangle texture formation in hot-dip galvanizing

The surface of a hot-dip galvanized layer is characterized by a beautiful solidification pattern of large Zn grains with a {0001} texture, which is called the spangle. The formation mechanism for the {0001} spangle texture has not yet been conclusively clarified. In this study, dendrite growth in a thin coating layer with Zn-0.2 wt%Al was systematically simulated in two dimensions using the phase-field method. As a result of the simulations, the {0001} texture is not formed when considering only the anisotropy of the solid–liquid interface energy. On the other hand, when considering the anisotropy of mobility, a clear {0001} texture is observed. Thus, it is concluded that the formation of the {0001} spangle texture may result from mobility anisotropy.

Role of Integrated Nutrient Management and Agronomic Fortification of Zinc on Yield, Nutrient Uptake and Quality of Wheat

Phosphorus (P) and zinc (Zn) are essential plant nutrients, and their deficiency in soils and the antagonistic effect of P on Zn are important concerns world-over. Thus, a two-year (2012–13 to 2013–14) experimentation was carried out to assess grain yield, nutrient uptake and quality parameters of wheat by various levels of P and Zn. The results revealed that 50% recommended dose of P (RDP) through phospho-enriched compost (PEC) + 50% RDP through fertiliser and soil application of 12.5 kg ZnSO4.7H2O ha−1 + one foliar spray of 0.5% ZnSO4.7H2O recorded significantly higher grain yield (4.81 and 4.61 t ha−1, respectively), straw yield (7.20 and 6.92 t ha−1, respectively) and protein content (11.5% and 11.3%, respectively). The concentrations of Zn in grain (35.6%) and straw (57.3%) were not affected due to organic P application but 100% P through P fertilizer reduced the Zn content in the grains. Both soil and foliar application of Zn were found to be more promising in increasing Zn and Fe concentration in grains (37.5 and 30.9 mg kg−1, respectively) and straw (60.3 and 398 mg kg−1, respectively). Overall, the treatment combination of 50% RDP through PEC + 50% RDP through fertiliser and soil applied 12.5 kg ZnSO4.7H2O ha−1 + one spray of 0.5% Zn was beneficial in reducing antagonistic effect of P on Zn and increasing Zn and Fe concentration in wheat grain and, thus, could be used for improving the yield of Zn and Fe enriched wheat grains.

High-pressure torsion processing of Zn–3Mg alloy and its hybrid counterpart: A comparative study

Abstract Processing of metal hybrid nanocomposites have emerged in the recent years by means of solid-state reactions through severe plastic deformation techniques, resulting in heterogenous microstructures and mechanical properties. Despite the increased scientific interest in these unusual materials, little is known regarding their comparative attributes with respect to a homogeneous material having equivalent nominal composition. This work provides a direct comparison of the microstructure and the hardness evolution between a Zn–3Mg (wt.%) alloy and its hybrid counterpart, after high-pressure torsion (HPT) and after HPT followed by a post-deformation annealing (PDA) treatment. Experimental results indicate that both the alloy and the hybrid reach a similar level of grain refinement after HPT processing, however, grain growth follows different trends after PDA. The HPT-processed alloy exhibits clusters of Mg2Zn11 nanocrystalline domains that coalesce into coarser grains maintaining a unimodal GS distribution after PDA. On the other hand, the hybrid after PDA displays a multimodal GS distribution consisting of ultrafine Mg-rich grains containing MgZn2 and Mg2Zn11 nanoscale intermetallics, in a matrix of coarser dislocation-free Zn grains. These observations were supported by kernel average misorientation (KAM) maps and pole figures obtained through electron backscattered diffraction (EBSD) analysis.

Microstructure evolution of a high-strength low-alloy Zn–Mn–Ca alloy through casting, hot extrusion and warm caliber rolling

Through casting, hot extrusion and then warm caliber rolling, biodegradable Zn-0.8Mn-0.4Ca alloy exhibits yield strength (YS) of 245 MPa, ultimate tensile strength (UTS) of 323 MPa, and elongation to failure (EL) of 12%. Its strengths are better than most of the existing biodegradable Zn alloys with ELs of 10–15%. So the alloy can be considered as a more competitive candidate for making bone screws or intravascular stents. Ca has a high efficiency of forming CaZn13 phase, the equilibrium volume fraction of which reaches 10.23 vol% with the minor addition of 0.43 wt% Ca. The CaZn13 particles not only impede dislocation motion, but also stimulate recrystallization of Zn grains, resulting in a considerable strengthening effect. The average size of Zn dendrites in the as-cast alloy reaches 289 μm, while that of Zn grains in the as-rolled alloy is 5.0 μm. On the other hand, the minor Ca addition severely decreases the ductility of the Zn-0.8Mn base alloy due to the large size of CaZn13 particles inherited from the as-cast microstructure. Although their average size is reduced to 12.9 μm after the caliber rolling, it is about five times of that of MnZn13 particles. For design and fabrication of Ca-containing Zn alloys in future, refinement of CaZn13 phase should be a matter of vital concern.

Microstructure and mechanical properties of extruded and caliber rolled biodegradable Zn-0.8Mn-0.4Ag alloy with high ductility

Caliber rolling can be a processing step of biodegradable Zn alloys for making implant devices such as stents and bone screws. However, effects of caliber rolling on microstructures and mechanical properties of biodegradable Zn alloys are seldom investigated. In the present study, it is employed in order to strengthen extruded Zn-0.8Mn-0.4Ag alloy. The as-rolled alloy has yield strength (YS) of 173.4 MPa, ultimate tensile strength (UTS) of 262.2 MPa and elongation to failure (EL) of 46.0%. Before the rolling, the as-extruded alloy has a bimodal Zn grain structure featured by very large Zn grains longer than 87 μm and fine Zn grains of 5.5 μm, which endows it a high EL of 62.6%. After the rolling, the bimodal structure is replaced by a uniform grain structure with finer Zn grains of 4.0 μm. MnZn13 grains are also refined from 6.7 μm to 4.2 μm. Twinning happens not only in Zn grains, but also in MnZn13 grains. The large Zn grains are more prone to be twinned, while multiple narrow twins with width as small as about 22 nm form in a MnZn13 particle. The grain refinement strengthens the alloy, while the bimodal grain structure toughens the alloy. The rolling achieves a more thorough grain refinement, meanwhile it annihilates the bimodal grain structure, resulting in a strengthening effect in sacrifice of ductility. However, the ductility of the as-rolled alloy is still higher than most biodegradable Zn alloys.

Microstructure and Mechanical Properties of Zamak 3 Alloy Subjected to Sliding Friction Treatment

With aim to enhance the understanding of the relationship between the microstructure and mechanical properties of severe plastic-deformed Zn alloys, this work investigates the microstructural evolution and underlying deformation mechanisms of Zamak 3 alloy subjected to sliding friction treatment (SFT). With an increase in the strain from the matrix to the surface of the SFT Zn alloy, three types of microstructural characteristics are observed: (i) Gradual refinement of the Zn grains, (ii) First increase and then decrease in twin density, and (iii) Gradually elongated/broken eutectic phases. The results of mechanical tests reveal that work hardening plays a dominant role until strong softening resulting from microstructural refinement. The competition between hardening and softening related to the microstructural evolution determines the specific mechanical properties of Zn alloys.

Effects of Zn on intermetallic compounds and strength of Al/Mg joints ultrasonically soldered in air

Dissimilar Al/Mg alloys were soldered by changing the Zn content in Sn-based solders with the assistance of ultrasonic. Results showed that the Al/Mg intermetallic compounds (IMCs) of Al3Mg2 and Al12Mg17 were avoided, but a new IMC of Mg2Sn formed in the joints. Mg2Sn was blocky inside the joints and continuous near the Mg side. Blocky Mg2Sn did not present a connection to the continuous Mg2Sn in joints soldered by Sn–16Zn. The shear strength of the joints increased with the addition of Zn into the solders. The maximum shear strength of 49 MPa was obtained when the Sn–16Zn solder was used. The Al content exceeded its ultimate solution in the solder and increased with increasing Zn. The floating of Al grains was observed in the joints soldered by Sn, Sn–3Zn, and Sn–9Zn because of sound radiation pressure, which was blocked by Zn grains in the joint soldered by Sn–16Zn.

Refined Lamellar Eutectic in Biomedical Zn–Al–Zr Alloys for Mechanical Reinforcement

Zn is recognized as a bone implant metallic material owing to its natural biodegradability and good biocompatibility. In this study, refined lamellar eutectic is constructed in Zn alloys by alloying with Al and Zr via selective laser melting, aiming to improve its mechanical strength. The results demonstrate that lamellar eutectic forms along the grain boundaries due to the alternating solidification of Zn‐ and Al‐enriched phases. The lamellar eutectic not only refine Zn grains but also provide numerous phase interfaces for dislocation pile‐up. More importantly, Al2ZnZr phase is also found in the alloys and acts as heterogeneous nucleation sites for Al‐enriched phase, which is beneficial for the formation of lamellar eutectic. With Zr content increasing to 0.2 wt%, the amount of Al2ZnZr phase increases, leading to more lamellar eutectic formation. This reduces the lamellar spacing to 0.34 ± 0.03 µm, providing more phase interfaces for slip interference. As a result, as compared with Zn, the Zn–7Al–0.2Zr alloy presents 179 ± 12% improvement in mechanical strength, which is comparable to the strength criteria for bone implants. In addition, the degradation rate increases from 0.08 ± 0.03 mm year−1 to 0.15 ± 0.03 mm year−1 due to the enhanced galvanic corrosion between Zn‐ and Al‐enriched phases. Cytocompatibility evaluation also indicates that the Zn–7Al–Zr alloys present good biocompatibility to MG‐63 cells.

Microstructure and corrosion properties of zinc-graphene oxide composite coatings

Microstructure and corrosion properties of electrodeposited zinc-graphene oxide (Zn-GO) composite coatings and Zn-GO-Zn multilayer coating was investigated. Addition of GO enhanced the corrosion resistance of the composite coating. Microstructural characterization revealed that the enhancement in the corrosion resistance was due to GO induced significant reduction in Zn grains sizes which would facilitate formation of protective oxide layer. Microstructural characterization of exposed Zn-GO-Zn multilayer coatings revealed relatively lesser oxidation of Zn regions beneath the GO layer which further illustrated the role of impermeability of GO towards hindering the penetration of the electroactive media and thereby retarding the corrosion rate.

Influence of solution heat treatment on microstructure and hardness of as-cast biodegradable Zn–Mn alloys

Zn–(< 1 wt%)Mn alloy is a promising base alloy for developing biodegradable Zn–Mn-based alloys with high strength and high ductility. In this paper, the influence of solution heat treatment on microstructure and hardness of as-cast Zn–0.34Mn and Zn–0.76Mn alloys has been investigated. The temperature of 380 °C is a good choice for the solution heat treatment. ζ-MnZn13 phase is completely dissolved in Zn matrix after 20 h for Zn–0.34Mn alloy and after 30 h for Zn–0.76Mn alloy. Unexpectedly, temporary precipitation of ζ-MnZn13 is observed within grains of Zn–0.76Mn alloy at 5 h, which reaches the peak at 10 h and then decreases until it finally disappears. During the solution heat treatment, hardness of the Zn–Mn alloys decreases with time. Zn–0.76Mn alloy is always about 4–8 HV harder than Zn–0.34Mn alloy. The temporarily formed ζ-MnZn13 particles are rod-like or lath shaped. The orientation relationship between a representative lath-shaped ζ-MnZn13 precipitate and Zn matrix can be described as [101]ζ~//[2-1-10]m and (-131)ζ ~ 5.4° from (0002)m, which is firstly reported as far as our knowledge. The ζ-MnZn13 lath has the long axis parallel to [03-32]m and the habit plane parallel to (-111)ζ//(0-113)m. Simulation of lattice matching reveals that every two ζ-MnZn13 lattice sites match with one Zn lattice site along the direction of the long axis, which explains why the precipitate grows along this direction. No serious segregation of Mn is detected within Zn grains in the as-cast Zn–0.76Mn alloy. The reason why ζ-MnZn13 precipitates temporarily form during the solution heat treatment requires further investigation.

Free-Cyanide Synthesis and Characterization of Cu–Zn Alloy by an Electrodeposition-Annealing Route

Substitution of cyanide in electroplating is a current challenge. We present an alternative method aiming to reduce the toxicity and the cost of electroplating of Cu–Zn alloy (usually prepared from cyanide baths) while maintaining the decorative qualities and anticorrosive properties of the coating. For this purpose, Cu–Zn alloys were obtained in two steps from non-cyanide electrolytes. First, a copper layer electrodeposited onto a nickel under-layer, followed by a thin layer of zinc from three different simple non-cyanide zinc baths. The Zn/Cu/Ni sandwich system was then subjected to heat treatment at a temperature of 400°C, to ensure the diffusion of zinc into the copper layer to give the desired Cu–Zn alloy structure. The synthesized films were characterized by using X-ray diffraction XRD, scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS). XRD demonstrated that the electrodeposited films are crystalline and present the Cu0.7Zn0.3 phase with preferential (111) orientation. An analysis of XRD patterns revealed that after heat treatment, the Cu–Zn alloys were composed of a predominating α-phase structure. The morphology and composition of the coatings depends on the zinc plating bath type. After annealing, well defined pseudospherical Cu–Zn grains were formed covering the entire substrate surface. The EDS analysis indicated the formation of Cu0.7Zn0.3 brass alloys. The results showed the feasibility of this low-cost new route for the preparation of good quality Cu–Zn alloys from cyanide-free electrolytes.

Selective laser melting of Zn–Ag alloys for bone repair: microstructure, mechanical properties and degradation behaviour

ABSTRACT Zn possesses good biodegradability and biocompatibility, but its strength and hardness are insufficient for bone implants. In this study, Ag was introduced into Zn to improve the mechanical properties by selective laser melting. The results showed that Ag was dissolved in Zn, which generated constitutional undercooling in front of the advancing solid/liquid interface during solidification, making more nucleation events occur and thus refining the grains. When Ag content exceeded its solid solubility in Zn, AgZn3 phase is formed, which acted as active nucleation sites for Zn grains, further refining the grains. The refinement of the grains effectively hindered the plastic deformation and dislocation. As a result, the compressive strength and hardness were improved by about 100% and 116%, respectively. When Ag content continued increasing and became excessive, AgZn3 phase grew rapidly, coarsening the grains. Accordingly, the mechanical properties slightly decreased. These results demonstrated that the Zn–Ag alloys are potential implant biomaterials.

Microalloyed Zn-Mn alloys: From extremely brittle to extraordinarily ductile at room temperature

Zn-0.34Mn and Zn-0.76Mn alloys transit from extremely brittle in as-cast status to extraordinarily ductile with elongations ranging from 88.8% to 94.0% at room temperature through 83.3% hot-rolling, annealing at 200 °C for 2 h and then air cooling, and finally 84% cold-rolling. Both the hot-rolling and the cold-rolling greatly refine Zn grains, while the annealing changes rolled textures into annealed textures. Grains in the as-cold-rolled alloys are smaller than 3 μm. After tensile testing, Zn grains close to the fracture are predominantly equiaxed rather than elongated. An aggregation or a long band of very fine Zn grains smaller than 1 μm is revealed in regions close to the fracture. The extraordinary ductilities of the alloys owe to fine grains before tensile testing and dynamic recrystallization during tensile testing, which helps to relieve accumulated stress.

Effects of nanoparticles on the thermal, microstructural and mechanical properties of novel Sn3.5Ag0.5Zn composite solders

The effects of added nanoparticles (i.e., Al2O3 and TiO2) on the thermal, microstructural and mechanical properties of Sn3.5Ag0.5Zn nanocomposite solders have been investigated. Adding nanoparticles to the Sn3.5Ag0.5Zn solder increases the melting temperature by only 2.1–4.6 °C. It was also confirmed that the nanoparticles affect the microstructural and mechanical properties. The UTS, 0.2 YS, and microhardness of the Sn3.5Ag0.5Zn nanocomposite solder improved, which could be attributed to the refinement of the β-Sn grain size, the precipitation of Ag3(Sn, Zn) grains, and the second phase dispersion strengthening mechanism. The fracture mechanism of Sn3.5Ag0.5Zn nanocomposite solders was confirmed to be the ductile fracture mode. The cracks were initiated at the interfaces between β-Sn(Zn) grains and Ag(Zn, Sn) phases.

Transformation from Film to Nanorod via a Sacrifical Layer: Pulsed Laser Deposition of ZnO for Enhancing Photodetector Performance

A novel fabrication method for single crystalline ZnO nanorods by pulsed laser deposition (PLD) using a chemical-bath-deposited ZnS seed layer is proposed. For the substrate temperature (Ts) lower than 700 °C, the PLD-ZnO showed a polycrystalline phase and film-type morphology, resulting from the ZnS seed layer with a cubic phase. However, the ZnS film became a sacrifical layer and single crystalline ZnO(002) nanorods can be achieved at Ts of 900 °C, where ZnS was decomposed to zinc metals and sulfur fumes. The transformation from ZnO film to nanorod microstructure was demonstrated with the change of ZnS layer into Zn grains. Enhanced performance of the metal-semiconductor-metal photodetectors were fabricated with ZnO/ZnS samples grown at Ts of 500, 700, and 900 °C. The responsivities (@1 V and 370 nm) of these three devices were 1.71, 6.35, and 98.67 A/W, while their UV-to-visible discrimination ratios were 7.2, 16.5, and 439.1, respectively. Obviously, a higher light-capturing efficiency was obtained in the 900 °C-grown ZnO/ZnS device owing to its one-dimensional nanostructure with high crystal quality. The results indicate PLD combined with a sacrifical nanostructure is a promising method for obtaining high-quality ZnO nanorods, which paves the way for the fabrication of high performance ZnO-based devices.

Fabrication of Cu2ZnSnS4 thin film solar cells by annealing of reactively sputtered precursors

The Cu2ZnSnS4 (CZTS) absorbers for thin film solar cells were fabricated by reactive sputtering followed by post-annealing. The effects of annealing temperature and Cu/(Zn + Sn) ratio on the film microstructure and related device performance were systematically investigated. It was found that the higher annealing temperature facilitates Zn incorporation and grains growth, but leads to more Sn loss and thicker MoS2 layer. The CZTS absorbers with a lower Cu/(Zn + Sn) ratio show larger grain size and more ZnS particles on the surface, whereas the films with higher Cu content (Cu/Sn > 2) demonstrate small grain size, much Cu2−xS phases and cracks. The highest device efficiency of 3.72% was obtained from the CZTS film annealed at 570 °C with Cu/(Zn + Sn) ratio of 0.78. The performance of devices is limited by low Jsc and FF due to the interface recombination and the block of carrier transport by ZnS.

Effect of Mg content on microstructure and corrosion behavior of hot dipped Zn–Al–Mg coatings

In this article, Zn–Al–Mg coatings were prepared by hot dipping method. The surface morphology, cross–section microstructure, microhardness, composition, corrosion behaviour of ZAM coatings were investigated by using X–ray diffraction (XRD), Optical microscope, Environmental scanning electron microscopy equipped with EDS (FESEM–EDS), Microhardness tester and Electrochemical analysis respectively. Corrosion test was also performed in a standard salt fog spray chamber. Microstructure studies indicates that Zn grain size was refined and eutectic areas at Zn grain boundary areas increased with increasing Mg content. ZA5M1.5 and ZA5M2 coatings have two distinct layers. Mg tends to exist in the outer layer while Al is in the inner layer. The inner layer is composed of Al5Fe2Zn0.4 intermetallic, which may to contribute to the microhardness. The outer layer is Zn grains surrounded by Zn–Mg etutectics, which may improve the corrosion resistance. The microhardness is more than 700 HV50g for Al-rich layer and around 151 HV25g for Mg-rich layer. The improved corrosion resistance of Zn–5%Al-1.5%Mg coating comes from the corrosion product of flocculent type simonkolleite, which prolongs the micro-path and impedes the movement of O2 and H2O, ultimately retards the overall corrosion process.

Structure, mechanical characteristics and in vitro degradation, cytotoxicity, genotoxicity and mutagenicity of novel biodegradable Zn-Mg alloys.

Zn-(0-1.6)Mg (in wt.%) alloys were prepared by hot extrusion at 300 °C. The structure, mechanical properties and in vitro biocompatibility of the alloys were investigated. The hot-extruded magnesium-based WE43 alloy was used as a control. Mechanical properties were evaluated by hardness, compressive and tensile testing. The cytotoxicity, genotoxicity (comet assay) and mutagenicity (Ames test) of the alloy extracts and ZnCl2 solutions were evaluated with the use of murine fibroblasts L929 and human osteosarcoma cell line U-2 OS. The microstructure of the Zn alloys consisted of recrystallized Zn grains of 12 μm in size and fine Mg2Zn11 particles arranged parallel to the hot extrusion direction. Mechanical tests revealed that the hardness and strength increased with increasing Mg concentration. The Zn-0.8 Mg alloys showed the best combination of tensile mechanical properties (tensile yield strength of 203 MPa, ultimate tensile strength of 301 MPa and elongation of 15%). At higher Mg concentrations the plasticity of Zn-Mg alloys was deteriorated. Cytotoxicity tests with alloy extracts and ZnCl2 solutions proved the maximum safe Zn(2+) concentrations of 120 μM and 80 μM for the U-2 OS and L929 cell lines, respectively. Ames test with extracts of alloys indicated that the extracts were not mutagenic. The comet assay demonstrated that 1-day extracts of alloys were not genotoxic for U-2 OS and L929 cell lines after 1-day incubation.

Crystallography of grain refinement in cast zinc–copper alloys

Adding the peritectic forming element Cu effectively reduced the average grain size of cast Zn by over 85%. At a specified cast condition, the smallest grain size was obtained at 2 wt% Cu addition. A further increase in Cu content led to grain coarsening in the cast Zn–Cu alloys. Although the solute effect of Cu was predominately responsible for the grain refinement through restriction of the grain growth, it was found that the variation of grain size is also closely related to the formation of the pro-peritectic phase, ɛ-CuZn4. Crystallographic calculations using the edge-to-edge matching model showed low interatomic misfit and interplanar mismatch between Zn and the ɛ-CuZn4 phase. In addition, a reproducible h.c.p.–h.c.p. (h.c.p. denotes hexagonal close-packed) orientation relationship between Zn and the ɛ-CuZn4 particles (located within the Zn grain centres) was also experimentally determined using the electron backscattered diffraction method. This indicated the high potency of the pro-peritectic ɛ-CuZn4 particles as effective heterogeneous nucleation sites for η-Zn, which further refined the Zn grains. However, when the Cu content was over 2.0 wt%, formation of large ɛ-CuZn4 particles resulted in grain coarsening of the cast alloys.