Molten Zn Research Articles

The growth kinetics of intermetallic compounds by the fast diffusion path at the interface of Co and molten Zn

This study investigates the growth and microstructure formation of intermetallic compounds at the solid/liquid interface of a Co/Zn diffusion couple prepared using an isothermal bonding method and annealed isothermally at 703 K, 723 K, and 743 K for up to 48 h. The experimental observations and analysis revealed the formation of three Zn-rich intermetallic compounds: γ (Co5Zn21), γ1 (CoZn7), and γ2 (CoZn13). The γ2 phase, having the highest Zn content, formed the thickest layer, while the γ and γ1 phases exhibited slower growth. The total thickness of these layers increased proportionally to the annealing time, following a power function. The growth of intermetallic compounds was predominantly controlled by interdiffusion, with the γ2 phase forming island-like structures that merged over time, creating fast diffusion paths of liquid Zn. The annealing temperature had a minimal impact on the growth rate, with slightly faster growth observed at lower temperatures due to finer needle-like interfaces within the molten Zn, which created more efficient diffusion paths. These findings underscore the importance of understanding the kinetics and mechanisms of intermetallic compound formation for optimizing material properties and processing conditions in industrial applications.

Al2O3 Coatings for Protection of Stainless Steel 316L against Corrosion in Zn-Al and Zn-Al-Mg

The production and quality of automotive-grade galvanised steel are affected by the limited service life of the pot roll bearings used in continuous galvanising lines. The journal bearings are subjected to severe degradation as they react with the molten Zn bath, and coatings can provide corrosion protection to the bearing materials. This research investigates the performance of Al2O3 coatings applied via the HVOF thermal spray process to stainless steel 316L substrates. Immersion tests were conducted in baths of different compositions, namely GI (Zn-0.3 wt.% Al) and ZMA (Zn-1.5 wt.% Al-1.5 wt.% Mg). Material characterisation after testing showed evidence of coating degradation after 1 week, as the coating tended to crack and detach from the substrate, allowing the molten Zn to attack the underlying steel. The coefficient of thermal expansion of Al2O3 and steel was measured, and a difference of 13 × 10−6 K−1 was found, leading to the development of cracks in the coatings. Zn penetration through cracks was determined to be the main failure mechanism of the Al2O3 coatings, which otherwise remained inert to Zn-Al. Conversely, the coatings immersed in Zn-Al-Mg reacted with the Mg in the molten metal bath, showing that changing bath composition affected the performance of the coatings in molten Zn alloy.

In-Situ Wettability Analysis of Al Coating Influence on Hot-Dip Galvanizing Properties of Advanced High-Strength Steels

We investigated the influence of steel surface properties on the wettability of zinc (Zn). Our main objective is to address the selective oxidation of solute alloying elements and enhance the wetting behavior of Zn on advanced high strength steel (AHSS) by employing an aluminum (Al) interlayer through the physical vapor deposition technique. The deposition of an Al interlayer resulted in a decrease in contact angle and an increase in spread width as the molten Zn interacted with the Al interlay on the steel substrate. Importantly, the incorporation of an Al interlayer demonstrated a significant improvement in wettability by substantially increasing the work of adhesion compared to the uncoated AHSS substrate.

Densification mechanism of ZnO ceramics prepared by cold sintering with molten zinc acetate dihydrate as the transient liquid medium

The transportation of Zn2+ in acetic acid (HOAc) or Zn(OAc)2 water solution was considered crucial for the successful cold sintering of ZnO ceramics. However, our work shows that ZnO ceramics can even be densified by cold sintering with the aid of solid Zn(OAc)2·2 H2O without introducing extra free water. DSC-TG analysis reveals that pure Zn(OAc)2·2 H2O is dehydrated completely into solid Zn(OAc)2 during heating in an open environment, while it melts in ZnO-Zn(OAc)2·2 H2O mixture or a high-pressure and semi-closed circumstance due to the strongly suppressed dehydration. Consequently, molten Zn(OAc)2·2 H2O acts as the transient liquid medium for the dissolution-precipitation process at over 100 °C, and plays a dominant role in the densification, microstructural evolution, and mechanical robustness of the cold-sintered ZnO ceramics. The densification mechanism is confirmed by the pressure-time curves, and reveals a novel strategy for cold sintering of water-insoluble ceramics by introducing molten hydrated salt or alkali as the transient liquid medium.

Tio2 and Nickel Coatings on Resistance Welding Electodrs to exetended Life Using Chemical Vapour Desposition Process

TiO2/Ni coating has been deposited onto the electrodes by chemical vapour deposition to improve electrode life during resistance welding of Zn- coated steels. However, welding results revealed that molten Zn penetrates into coating through the cracks and then reacts with substrate copper alloy to form brasses. In the present work, laser treatment was performed on the TiO2/Ni coated electrodes to eliminate cracks formed in the as-deposited TiO2/Ni coating. In addition, a chemical vapour deposition of Ni, TiO2/Ni and Ni has also been carried out to improve coating quality. On the other hand, a Ti coating was also investigated. Those coatings were characterized by electro-microscopy, energy- dispersive X-ray analysis, X-ray diffraction and micro-hardness tests. The results showed that cracks within the as-deposited TiO2/Ni coating could be eliminated with the use of laser treatment and chemical vapour deposition process. However, softening of copper substrate after laser treatment was a problem that restricted welding performance. Welding tests showed that the multi-layer TiO2/Ni coating acted as a better barrier to decrease alloying between the copper alloy and molten Zn as well as pitting (erosion) of electrode. The TiO2 coating demonstrates its potential application on the electrode to further improve the electrode’s life Key Word: Electrode; Molecular; Titanium; Nanotechnology; Nickel.

Effect of Zn-coating type on intergranular Cu-penetration in steels during weld-brazing

Weld-brazing has emerged as a promising alternative to fusion welding for joining Zn-coated advanced high strength steels (AHSSs) due to its lower heat input, reduced Zn burn-off, and elimination of defects like porosity and blowholes. Additionally, the weld-brazing process minimizes HAZ softening, a phenomenon that can affect joint strength. While weld-brazing can potentially eliminate the liquid metal embrittlement (LME) caused by the penetration of molten Zn into grain boundaries (GBs), this study found that galvanized (GI) DP600 steels were more susceptible to intergranular penetration of Cu into the substrate during weld-brazing compared to galvannealed (GA) DP600. Although no Zn-related LME was observed during arc-brazing with Si-Bronze filler, the potential for Cu-related LME cracks to form in GI coated steels may affect the mechanical integrity of the joint.

Microstructural evolution of a nickel-based single-crystal superalloy embrittled by molten Zn

The embrittlement treatment of Ni-based single-crystal superalloys in a Zn atmosphere causes the superalloys to break easily. This considerably increases the contact area in the dissolution process. Hence, this treatment has the potential for conveniently recovering rare precious metals from Ni-based superalloys. This study systematically examines the microstructures of Ni-based single-crystal superalloys after Zn embrittlement. Microstructural changes in the superalloy after reaction with Zn at 700, 900, 1100, and 1200 °C for 8 h were investigated and analyzed in detail via X-ray diffractometry, scanning electron microscopy, and electron probe microanalysis, using the phase and element composition as the evaluation indices. Results showed that the formation of the Ni5Zn21 intermetallic compound in the superalloys was the main reason. The formation of Ni5Zn21 disturbed the distribution balance and promoted the recombination of metallic elements, resulting in the embrittlement of the superalloys. The embrittlement mechanism involved a mutual diffusion reaction of Zn and Ni, but the degree of Zn diffusion was higher.

Effect of Antimony on Wetting Behavior and Interfacial Reaction between Zinc Liquid and X80 Steel

The wetting behavior of molten Zn and Zn-Sb alloy and X80 steel in a high vacuum environment was studied by the modified sessile drop method. The wetting morphology and interface structure were analyzed by scanning electron microscope and energy dispersive spectrometer. The results show when the content of Sb in Zn-Sb alloy increases from 0.0 wt. % to 1.0 wt. %, the initial contact angle between the droplet and the substrate decreases from 102.8° to 82.5°, and the equilibrium contact angle also decreases from 57.4° to 41.4°. Sb element in the Zn-Sb alloy can reduce the contact angle and improve the wettability due to its smaller surface tension. The spreading process of Zn-Sb alloys on X80 steel can be divided into rapid adsorption, reaction control, steady-state equilibrium stages, and Zn-Sb alloys with different mass fractions have the same spreading kinetics. The volatilized Zn element in the Zn-Sb alloy will reduce the oxide film on the surface of the substrate, making it easier for the Zn-Sb droplet to wet the steel plate and induce the formation of a precursor film. The formation mechanism of the precursor film is the subcutaneous penetration mechanism.

A novel Sb-Zn electrode with ingenious discharge mechanism towards high-energy-density and kinetically accelerated liquid metal battery

Liquid metal battery (LMB) has recently captured intensive attention for large-scale energy storage, originating from its attractive cost-efficiency, robust cyclability, and ultralong service lifetime. Nevertheless, realizing high energy density remains a great challenge. Herein, a novel dual-active Sb-Zn electrode is elaborately designed. A unique lithiation mechanism is demonstrated for the first time in LMB field. A ternary intermetallic compound LiZnSb is preferentially formed with a high discharge plateau at ca. 1.1 V, which is followed by a conversion reaction to Li3Sb and Zn at around 0.8 V and then a consecutive dissolution reaction of lithium in molten Zn, significantly ameliorating the voltage and capacity properties. Meanwhile, part Zn melts regenerate and disperse among discharge product layer, constructing rapid electron/lithium percolating networks in-situ, which accelerates the electrode reaction kinetics. As a result, the Li||Sb-Zn battery exhibits high average discharge voltage of 0.763 V at 100 mA cm−2 and superior rate performance (0.596 V at 1000 mA cm−2). Outstanding energy and power densities (290.6 Wh kg−1 and 239.66 W kg−1) are achieved, remarkably surpassing most reported LMBs and even comparable to Na-S battery. This work showcases an innovative electrochemistry system, opening a new avenue for high-performance LMBs.

Corrosion behavior of WC-η coatings in molten zinc

The WC-based coating containing a Co-W-C phase was fabricated to prevent steel components from molten Zn corrosion in galvanizing industry. The corrosion extent of the coating was determined through quantitative analysis of Co dissolved in molten Zn. It was found that slight oxidation of η phase by interstitial oxygen diffusion facilitated Zn substitution for Co and hence corrosion of the coating. The penetration rate of Zn from the sides of coating was significantly higher than that from the top surface. The formation of WO3/CoWO4 over the coating dramatically suppressed the dissolution corrosion process but may cause cracking and material exfoliation.

Formation and growth behavior of intermetallic compound phases in the interfacial reaction of solid Fe / liquid Zn at 450 °C

In the present study, the formation and growth behaviors of intermetallic compound (IMC) layers in the interfacial reaction of solid Fe and molten Zn during hot dipping at 450 °C were investigated. In the early stage of the interfacial reaction, Γ-Fe4Zn9, δ1k-FeZn7, and ζ-FeZn13 phases were formed, among which the growth of the ζ layer was dominant. Columns of the δ1p-Fe13Zn126 phase were formed on the δ1k/ζ interface at approximately 90 s, and the four IMC layers grew simultaneously until 600 s. Subsequently, a layer of the Γ1-Fe21.2Zn80.8 phase was formed along the Γ/δ1k interface and started growing, after which all the equilibrium IMC phases of Γ/Γ1/δ1k/δ1p/ζ grew competitively. The total thickness of the five IMC layers, dtotal, increased proportionally with the square root of the reaction time, t, i.e., dtotal = d0t0.5, which suggested that the growth of the entire IMC layers was controlled by the volume diffusion. However, the values of the time exponent, n, for the individual IMC layers differed depending on their microstructures and chemical concentrations, under equilibrium or nonequilibrium conditions. The formation of the multilayered columnar ζ phase can be attributed to the heterogeneous supersaturation of Fe in the liquid Zn near the columnar ζ / liquid Zn interface during the early stage of the interfacial reaction. The interdiffusion fluxes, J̃ϕ, of Fe and Zn in the ϕ phase (ϕ = Γ, δ1k, and ζ) were estimated from the measured concentration profiles of each phase. This suggested that J̃ϕ caused the growth of each phase as well as the supersaturation of Fe near the interfacial boundaries, thereby resulting in considerable deviations from the equilibrium concentrations. In the later stage of the interfacial reaction, the interfacial concentrations gradually approached the equilibrium concentrations with decreasing J̃ϕ.

Size-controllable zinc oxide nanowires fabricated via the combination of die-casting and oxidation process

Herein, we demonstrate a facile approach in the fabrication of one-dimensional ZnO nanowires (NWs) from the vacuum die-casting method in assistance with anodic aluminum oxide (AAO) template. The casting method enables molten Zn to embed uniformly over the AAO nanomould under high pressure and temperature of 500 °C. Besides, the significant influence of the oxidation time and temperature stimulates the ZnO NWs growth inside the AAO nanochannels. The oxidation in the nanochannels was profoundly controlled by the inward diffusion of oxygen atoms and the ZnO grows perpendicular towards the surface which obeys the parabolic law. The TEM and XRD results revealed the ZnO wurtzite crystalline structure with preferential orientation along the c-axis. The relationship between ZnO geometry and function of oxidation parameters is demonstrated by microscopic and spectroscopic analysis. The obtained NWs from the chemical etching process resulted in high crystalline, homogeneous, and high-aspect ratio ZnO NWs in relationship with the AAO pore dimension. Further, the as-prepared ZnO NWs electrical properties were measured in a four-electrode system through the single nanowire device fabricated by FIB. The obtained current-voltage characteristic curves exhibited hysterias loop in consequence with the space charge limited current effect of ZnO NW, which confirms its potential to be used in practical electronic applications.

Cladding thick Al plate onto strong steel substrate using a novel process of multilayer-friction stir brazing (ML-FSB)

Friction stir brazing (FSB) using a pinless tool together with a braze was developed to extend bond area over friction stir lap welding. When using a large pinless tool of Ø40 mm to clad 10 mm thick 5083Al plate to 16Mn steel by FSB with Zn braze, the thermomechanical effect was sufficient to achieve wetting on Al side by dissolving Al into molten Zn, but joint could not be formed due to poor wettability on steel side. To enhance mechanical disruption of oxide film on the steel, multilayer FSB (ML-FSB) process was proposed by adding a thin (3 mm thickness) and soft aluminum sheet as interlayer. The first FSB pass created bonding between the thin interlayer and steel substrate with 4.7 μm thick FeAl3 without Zn residue, having 55 MPa shear strength. The second FSB pass created bonding between the thin interlayer and thick 5083Al clad with a diffusion zone with a little Zn, having 50 MPa shear strength. This work provided a new way to fabricate “thick clad” layered composite with “strong substrate”, and suggested that mechanical route for strong substrate and metallurgical route (eutectic reaction) for Al for removing oxide film should be preferential and available in FSB.

Effect of Si/Mn Ratio on Galvannealing Behavior of Si-added Steel

The influence of the Si/Mn ratio on the galvannealing behavior of 1.5 wt% Si -1.5~2.5 wt% Mn-added steel in the Fe oxidation-reduction process was investigated. The Si/Mn ratio of the steel affected the formation of Si-containing oxides during the annealing process. The amount of SiO2 formed on the steel surface decreased with as the Si/Mn ratio decreased, while the amount of Mn2SiO4 increased. In addition, the internal oxide formed in a relatively narrow area near the surface in the lower Si/Mn ratio sample, which indicated that the content of solute Si near the surface was lower in the lower Si/Mn ratio sample. The galvannealing reaction was accelerated by decreasing the Si/Mn ratio of the steel. The species and morphology of the Si-containing oxides determined the galvannealing behavior of the Si-added steel. The Si-containing selective surface oxide affected the formation of the initial Fe-Zn intermetallic compounds (IMC) during hot-dipping in molten Zn. The formation of SiO2 was suppressed in the sample with the lower Si/Mn ratio, which resulted in accelerated Fe-Zn IMC formation. On the other hand, solute Si in the steel affected the growth of the Fe-Zn IMC during heating in the galvannealing process. The content of solute Si was assumed to be lower in the lower Si/Mn ratio sample, which resulted in acceleration of Fe-Zn IMC growth.

Effects of steel type and sandblasting pretreatment on the solid-liquid compound casting characteristics of zinc-coated steel/aluminum bimetals

Effects of zinc-coated steel type and steel surface sandblasting pretreatment in the solid-liquid compound casting of layered type steel/aluminum bimetals were investigated. The Zn coating behavior and its effects on interfacial microstructure evolution and fracture mechanism were also discussed. The aluminum fluidity in thin plate type flow channels formed by the steel insert and the mold wall primarily depended on the insert surface roughness and secondarily on the wettability. As-galvanized (GI) steel/aluminum bimetal joints showed the bonding strength of 20 MPa and more, while galvannealed (GA) steels showed poor bonding. The interfacial bonding zone consisted of most Al13Fe4, Al8Fe2Si, Al4.5FeSi intermetallic phases, as well as some Si phases. A low temperature and short time of the bonding reaction coupled with a high silicon content of the aluminum alloy suppressed the formation of Al5Fe2 phase. Oxide scales on the GA steel surface prevented the molten Zn coating from mixing with the aluminum melt. The Zn coating of GI steels was rapidly disappeared from the steel surface by the chemical affinity and surface energy-driven fluid flow as well as the diffusion, resulting in the formation of Zn-free intermetallic phases. The Zn coating of GI steels played a role in retarding the onset of bonding reaction. A long time sandblasting caused an excessive growth of intermetallic layers and the formation of Kirkendall voids on the steel side, resulting in the shift of main fracture sites and a slight decrease of the bonding strength.

Effect of Si/Mn Ratio on Galvannealing Behavior of Si-added Steel

The influence of the Si/Mn ratio on the galvannealing behavior of 1.5 wt% Si −1.5~2.5 wt% Mn-added steel in the Fe oxidation-reduction process was investigated. The Si/Mn ratio of the steel affected the formation of Si-containing oxides during the annealing process. The amount of SiO2 formed on the steel surface decreased with as the Si/Mn ratio decreased, while the amount of Mn2SiO4 increased. In addition, the internal oxide formed in a relatively narrow area near the surface in the lower Si/Mn ratio sample, which indicated that the content of solute Si near the surface was lower in the lower Si/Mn ratio sample. The galvannealing reaction was accelerated by decreasing the Si/Mn ratio of the steel. The species and morphology of the Si-containing oxides determined the galvannealing behavior of the Si-added steel. The Si-containing selective surface oxide affected the formation of the initial Fe–Zn intermetallic compounds (IMC) during hot-dipping in molten Zn. The formation of SiO2 was suppressed in the sample with the lower Si/Mn ratio, which resulted in accelerated Fe–Zn IMC formation. On the other hand, solute Si in the steel affected the growth of the Fe–Zn IMC during heating in the galvannealing process. The content of solute Si was assumed to be lower in the lower Si/Mn ratio sample, which resulted in acceleration of Fe–Zn IMC growth.

Effect of Al and Mg Contents on Wettability and Reactivity of Molten Zn–Al–Mg Alloys on Steel Sheets Covered with MnO and SiO2 Layers

The reactive wetting behaviors of molten Zn–Al–Mg alloys on MnO- and amorphous (a-) SiO2-covered steel sheets were investigated by the sessile drop method, as a function of the Al and Mg contents in the alloys. The sessile drop tests were carried out at 460 °C and the variation in the contact angles (θc) of alloys containing 0.2–2.5 wt% Al and 0–3.0 wt% Mg was monitored for 20 s. For all the alloys, the MnO-covered steel substrate exhibited reactive wetting whereas the a-SiO2-covered steel exhibited nonreactive, nonwetting (θc > 90°) behavior. The MnO layer was rapidly removed by Al and Mg contained in the alloys. The wetting of the MnO-covered steel sheet significantly improved upon increasing the Mg content but decreased upon increasing the Al content, indicating that the surface tension of the alloy droplet is the main factor controlling its wettability. Although the reactions of Al and Mg in molten alloys with the a-SiO2 layer were found to be sluggish, the wettability of Zn–Al–Mg alloys on the a-SiO2 layer improved upon increasing the Al and Mg contents. These results suggest that the wetting of advanced high-strength steel sheets, the surface oxide layer of which consists of a mixture of MnO and SiO2, with Zn–Al–Mg alloys could be most effectively improved by increasing the Mg content of the alloys.

Improving Corrosion Resistance of Ferrous Alloy to Molten Zn by Modifying the Laves Phase Characteristics

The Laves phase morphology in the Fe25Mo14Cr10Ni1Si (wt.%) alloy was modified by Si addition to improve the corrosion resistance of the ferrous alloy to molten zinc. The Si-containing alloy showed a woven, needle-like Laves phase with higher Mo content than that of the Fe25Mo14Cr10Ni alloy. Corrosion resistance to molten Zn for the Si-containing alloy was more than 20 times higher than that of the silicon-free alloy mainly as a result of the characteristics of the modified Laves phase. This phase was oriented perpendicular to the Zn-diffusion direction, which effectively prevented corrosion by the molten Zn, leading to a denser FeZn13 layer rather than the FeZn10 layer produced in the Fe25Mo14Cr10Ni alloy.

Microstructural Evolution of 11Al-3Mg-Zn Ternary Alloy-Coated Steels During Austenitization Heat Treatment

This study details the microstructural evolution of a commercial hot-dip 11Al-3Mg-Zn-coated steel during austenitization. After 5 minutes of austenitization at 1173 K (900 °C), the ternary alloy coating transformed to consist of a nearly pure Zn as the major layer, a Fe-Al alloy layer at the interface, and a thin oxide overlay. The Fe-Al alloy layer effectively acted as the inhibition layer to prevent Fe from diffusing and reacting with Zn, which in turn retained the molten Zn layer and the integrity of the surface oxide layer. Moreover, the potential difference between the 11Al-3Mg-Zn coating and the steel substrate remained similar after austenitization, signifying the resulting coating kept its sacrificial protection capability.

Recovery of Nickel from Nickel-Based Superalloy Scraps by Utilizing Molten Zinc

With the purpose of developing a new process for recycling nickel (Ni) directly from superalloy scraps, a fundamental study on the extraction and separation of Ni was carried out using molten zinc (Zn) as the extraction medium. In order to examine the reaction between molten Zn and the Ni-based superalloy, superalloy samples and Zn shots were heated at 1173 K (900 °C) for 6 hours. After heating, the superalloy samples fully reacted with Zn and dissolved in molten Zn. The Zn-alloyed sample obtained by slow cooling consisted of two separated upper and lower phases. In the upper part of the sample, only Zn and the Zn-Ni alloys were found; in the lower part, an intermetallic alloy consisting of refractory metals such as rhenium (Re) and tantalum (Ta) was found. This result shows that Ni and refractory metals contained in the scrap can be separated by utilizing the density differences between the Zn-Ni alloy and the refractory metals in molten Zn. Vacuum treatment of the upper part of the Zn-alloyed sample at 1173 K (900 °C) reduced the concentration of Zn in the sample from 97.0 to 0.4 mass pct. After Zn removal, a Ni alloy containing Ni with a purity of 85.3 to 86.1 mass pct and negligible quantities (<0.1 mass pct) of Re and Ta was obtained. Moreover, recovered Zn metal after distillation had a purity of more than 99.9 mass pct. Therefore, this process could be an environmentally sound recycling process that can recover Ni from superalloy scraps without the consumption of Zn or the generation of toxic wastes solutions.