Pct Zn Alloy Research Articles

Cellular Automata Modeling of Two Discontinuous Reactions in Fe-13.5 At. Pct Zn Alloy During Ageing and Annealing

Cellular Automata Modeling of Two Discontinuous Reactions in Fe-13.5 At. Pct Zn Alloy During Ageing and Annealing

Enhancement of the Strength–Ductility Balance in Cu–40 Pct Zn Alloy by Single Roll Drive Rolling and Cooling-Assisted Friction Stir Processing

Enhancement of the Strength–Ductility Balance in Cu–40 Pct Zn Alloy by Single Roll Drive Rolling and Cooling-Assisted Friction Stir Processing

Influence of Minor Cr-Additions to the Growth of Columnar Dendrites in Al-Zn Alloys: Influence of Icosahedral Short Range Order in the Liquid

The effect of minute Cr additions on dendritic growth directions in Al-20 wt pct Zn alloy has been investigated. As first evidenced by Gonzales and Rappaz (Metall Mater Trans A 37:2797–2806, 2006) Al-Zn alloys exhibit a Dendrite Orientation Transition (DOT), from 〈100〉 below 25 wt pct Zn to 〈110〉 above 60 wt pct, regardless of the solidification speed. The DOT has been interpreted as a modification of the solid–liquid interfacial energy anisotropy (Gonzales and Rappaz, 2006; Haxhimali et al. in Nat Mater 5:660–664, 2006). However, 0.02 to 0.1 wt pct addition of Cr in Al-20 wt pct Zn drastically modifies the dendrite trunk direction from 〈100〉 to 〈110〉 at low solidification speed, typically 200 μm/s. Even more surprising, 〈100〉 dendrite trunks are retrieved in Al-20 wt pct Zn-0.1 wt pct Cr when the speed is increased to 1000 μm/s, but with the concurrent formation of twinned dendrites. Minute additions of Cr have been reported recently to promote icosahedral short range order (ISRO) in liquid Al-Zn, thus reducing the atomic mobility (Kurtuldu et al. in Acta Mater 115:423–433, 2016) and modifying the nucleation kinetics (Kurtuldu et al. in Acta Mater 61:7098–7108, 2013). The present results indicate that ISRO also modifies the attachment kinetics of icosahedral clusters rather than individual atoms, and is most likely responsible of growth direction change in Al-Zn-Cr alloy and of twinned dendrites formation.

In Vitro Biodegradation and Mechanical Properties of Mg-Zn Alloy and Mg-Zn-Hydroxyapatite Composite Produced by Mechanical Alloying for Potential Application in Bone Repair

A biodegradable Mg-6.5 wt pct Zn (Mg-Zn) alloy and Mg-6.5 wt pct Zn reinforced with 10 wt pct hydroxyapatite (HA) composite were prepared by mechanical milling. In vitro biodegradation activity as a function of immersion time was performed in Hank’s balanced salt solution (HBSS). The dissolution of Mg ions (Mg2+) decreased from 75.74 µg/ml of pure Mg to 59.24 µg/ml and 46.88 µg/ml corresponding to the Mg-Zn alloy and Mg-Zn/HA composite, respectively. This finding indicates the progressive effect of HA followed by the Zn addition in decelerating the degradation rate of Mg. More positive corrosion potential of Mg-6.5 wt pct Zn alloy (− 1.5015 V) and Mg-Zn/10 wt pct HA composite (− 1.4647 V) than that of pure Mg (− 1.6972 V) suggested that the Mg-Zn/10 wt pct HA composite exhibited the highest corrosion resistance in the bioenvironment. The compressive strength values after 7 days of immersion in HBSS of the Mg-Zn alloy and Mg-Zn/HA composite are 230.64 and 278.46 MPa, respectively, and these are considerably higher compared to the compressive strength of the cortical bone (100 to 230 MPa).

In Situ Observation of the Zr Poisoning Effect in Al Alloys Inoculated by Al-Ti-B

In situ synchrotron X-ray radiography observations of the Zr-poisoning phenomenon of an Al-20 wt pct Zn alloy inoculated by Al-5Ti-1B were carried out. The effects of Zr addition on heterogeneous nucleation, grain growth, and final grain size were quantitatively studied and further analyzed using the interdependence model. The experimental results show that the undercooling needed for nucleation increases and the nucleation rate decreases at the early stage of solidification with Zr addition, resulting in fast grain growth, a high solidification rate and increased severity of solute segregation in the solid–liquid coexistence regions. At the same time, the poisoning is a progressive process that is enhanced with the increasing Zr content, holding temperature, and holding time. The nucleation-free zone of the Zr-containing sample, either measured from the radiographs or calculated by the interdependency theory, is larger than that of the Zr-free sample. Our analysis shows that both the increase in the nucleation-free zone and the average interparticle spacing of the most potent available nucleation particles contribute to the increase of the grain size caused by Zr poisoning.

Enhanced Mechanical Properties and Corrosion Behavior of Biodegradable Mg-Zn/HA Composite

Magnesium (Mg) and its alloys have shown potential for use in the biomedical industry due to their excellent biological performance and biodegradability in the bioenvironment. Thus, the aim of the present study was to develop a reliable biodegradable hard tissue substituent. Biodegradable and bioactive Mg-Zinc (Zn) reinforced by hydroxyapatite (HA) composite was prepared using mechanically alloyed Mg-6.5 wt pct Zn and pure HA powders as starting materials. Various HA contents (i.e., 5, 10, 15, and 20 wt pct) were introduced in forming the Mg-Zn/HA composite. The effect of bioactive HA incorporation in biodegradable Mg-6.5 wt pct Zn alloy matrix on mechanical and biodegradation properties as well as microstructural observation was investigated. As measured by the Williamson–Hall formula, the Mg crystallite size of the sintered composites containing 5, 10, 15, and 20 wt pct HA were 36.76, 29.08, 27.93, and 27.31 nm, respectively. According to X-ray diffraction (XRD) analysis, there was no new crystalline phase formed during milling, indicating that no mechanochemical reactions between Mg-Zn alloy and HA occurred. The −1.70 V shifted significantly toward the passive position of the plain Mg-6.5 wt pct Zn alloy and Mg-Zn/10 wt pct HA composite, which were −1.50 and −1.46 V, respectively, indicating that the Mg-Zn/10 wt pct HA composite was least susceptible to corrosion in the bioenvironment.

High-Speed Synchrotron X-ray Imaging Studies of the Ultrasound Shockwave and Enhanced Flow during Metal Solidification Processes

The highly dynamic behavior of ultrasonic bubble implosion in liquid metal, the multiphase liquid metal flow containing bubbles and particles, and the interaction between ultrasonic waves and semisolid phases during solidification of metal were studied in situ using the complementary ultrafast and high-speed synchrotron X-ray imaging facilities housed, respectively, at the Advanced Photon Source, Argonne National Laboratory, US, and Diamond Light Source, UK. Real-time ultrafast X-ray imaging of 135,780 frames per second revealed that ultrasonic bubble implosion in a liquid Bi-8 wt pctZn alloy can occur in a single wave period (30 kHz), and the effective region affected by the shockwave at implosion was 3.5 times the original bubble diameter. Furthermore, ultrasound bubbles in liquid metal move faster than the primary particles, and the velocity of bubbles is 70 ~ 100 pct higher than that of the primary particles present in the same locations close to the sonotrode. Ultrasound waves can very effectively create a strong swirling flow in a semisolid melt in less than one second. The energetic flow can detach solid particles from the liquid–solid interface and redistribute them back into the bulk liquid very effectively.

Evaluating the Superplastic Flow of a Magnesium AZ31 Alloy Processed by Equal-Channel Angular Pressing

Experiments show that the magnesium AZ31 (Mg-3 pct Al-1 pct Zn) alloy exhibits excellent superplastic properties at 623 K (350 °C) after processing by equal-channel angular pressing using a die with a channel angle of 135 deg and a range of decreasing processing temperatures from 473 K to 413 K (200 °C to 140 °C). A maximum elongation to failure of ~1200 pct was achieved in this alloy at a tensile strain rate of 1.0 × 10−4 s−1. Microstructural inspection showed evidence for cavity formation and grain growth during tensile testing with the grain growth leading to significant strain hardening. An examination of the experimental data shows that grain boundary sliding is dominant during superplastic flow. Furthermore, a comprehensive review of the present results and extensive published data for the AZ31 alloy shows the exponent of the inverse grain size is given by p ≈ 2 which is consistent with grain boundary sliding as the rate-controlling flow mechanism.

Morphology and Growth Kinetic Advantage of Quenched Twinned Dendrites in Al-Zn Alloys

Twinned dendrites appearing in an Al-26 wt pct Zn alloy have been quenched during growth using a specifically designed setup that is positioned on top of a directional solidification experiment. X-ray tomography performed at the Swiss Light Source (SLS-beamline TOMCAT) allowed us to reconstruct the 3D morphology of these structures and to confirm previous observations performed on single 2D sections (Henry et al., Metall Mater Trans A 35A:2495–2501, 2004; Salgado-Ordorica and Rappaz, Acta Mater 56:5708–5718, 2008). Further characterization of these quenched specimens led to a better description of the mechanisms involved in the in-plane and lateral growth propagation of twinned dendrites. These were then put into relation with the competition mechanisms taking place during simultaneous solidification of twinned and regular dendrites.

Grain Size Hardening in Mg and Mg-Zn Solid Solutions

Cast specimens of Mg and of several Mg-Zn binary alloys with a wide range of grain sizes were deformed in tension and compression. The k values calculated from the Hall–Petch (H-P) plots of the tensile 0.2 pct proof stress increased with the Zn content, from 0.24 MPa m1/2 for pure Mg to ~0.66 MPa m1/2 for the 2.3 at. pct Zn alloy; k values measured from compression tests were larger, typically by 0.05 MPa m1/2. When the strength measurements were corrected for the pseudoelastic strain resulting from elastic twinning, the k values generally increased, and the difference between tension and compression was eliminated. This showed that the larger k values obtained in compression using uncorrected data were an artifact of the pseudoelastic effect. The apparent friction stress varied between about 14 MPa for pure Mg to very low or negative values for the most dilute alloy, increasing again to about 8 MPa for the most concentrated alloy. The use of strength data corrected for pseudoelasticity effects is necessary for a consistent analysis of the grain size hardening.

Effects of Processing Parameters on the Grain Refinement of Magnesium Alloy by Equal-Channel Angular Extrusion

The Mg-3 pct Al-1 pct Zn (AZ31) alloy has been used as a model material for understanding the grain-refinement process of a Mg alloy fabricated by equal-channel angular extrusion (ECAE). The effects of ECAE processing parameters on grain refinement have also been studied; it was found that these effects are quite different from those for fcc metals. A multitemperature extrusion procedure has been developed, which can produce an ultrafine-grained AZ31 alloy having a grain size 0.37 μm. For the AZ31 alloy, this ultrafine-grained alloy has a record high strength accompanied by reasonably good tensile ductility. The success of the development of this ECAE procedure proves that ECAE can offer a good opportunity for the development of high-strength Mg alloys.

Morphological and Microstructural Characterization of the Aragonitic CaCO3/Mg,Al-Hydrotalcite Coating on Mg-9 Wt Pct Al-1 Wt Pct Zn Alloy to Protect against Corrosion

This work presents a novel environmentally clean method for synthesizing the chemical conversion coating on Mg-Al-Zn (AZ91D) alloy surface and protecting the alloy from corrosion. An aragonitic CaCO3/Mg,Al-hydrotalcite two-layer coating was first developed on the Mg alloy in an aqueous Ca2+/HCO3 − solution at 50 °C. When the Mg sample was immersed in a Ca2+/HCO3 − aqueous solution, corrosion occurred on the Mg sample surface, resulting in a high interfacial Mg2+ concentration and high pH value directly above the sample surface. The layer (Mg,Al-hydrotalcite) generated by corrosion formed on the Mg alloy when initially immersed in the Ca2+/HCO3 − solution. Temperature, solution pH, and presence of Mg2+ are important factors when determining the production yield of aragonitic CaCO3 particles. In this work, the high interfacial Mg2+ concentration and high pH directly above the sample surface induced preferential growth of CaCO3 on the Mg,Al-hydrotalcite layer, thereby forming a two-layer coating on the Mg alloy sample. Electrochemical tests using the polarization impedance method and salt spray test show that the CaCO3 coating protected the substrate metal from corrosion. Moreover, the CaCO3 layer markedly improved the galvanic corrosion resistance of the coated Mg alloys.

The microstructural development of Mg-9 pct Al-1 pct Zn alloy during injection molding

Ex-situ microstructural analysis was used in order to assess the high-temperature transformations of the Mg-9 pct Al-1 pct Zn alloy within the injection-molding system. In addition to as-cast ingot, chipped feedstock, and final products, the alloy samples at different stages of the process were investigated. It was revealed that the cold deformation during ingot chipping and recrystallization during initial stages of residency inside the barrel led to nucleation and growth of the equiaxed grain structure. Subsequent melting of the Al-rich phase followed by liquid-alloy wetting of α-Mg grain boundaries initiated the formation of the slurry with globular solid particles. The structural evolution of the semisolid alloy under the simultaneous influence of temperature gradient and injection-screw shear is considered, and the mechanisms involved are discussed. It is concluded that during processing of partially remelted alloy the temperature profile along the injection-molding barrel in combination with the feedstock structure are key factors that control both the transformation of the thixotropic slurry and the final morphology of the primary solid phase.

Solid solubility of carbon in a mechanically alloyed Cu-29.7 At. Pct Zn alloy

Solid solubility of carbon in a mechanically alloyed Cu-29.7 At. Pct Zn alloy

Processing, microstructure, and mechanical behavior of cast magnesium metal matrix composites

Magnesium metal matrix composites (MMCs) have been receiving attention in recent years as an attractive choice for aerospace and automotive applications because of their low density and superior specific properties. This article presents a liquid mixing and casting process that can be used to produce SiC particulate-reinforced magnesium metal matrix composites via conventional foundry processes. Microstructural features, such as SiC particle distribution, grain refinement, and particle/matrix interfacial reactions of the cast magnesium matrix composites, are investigated, and the effects of solidification-process parameters and matrix alloys (pure Mg and Mg-9 pct Al-1 pct Zn alloy AZ91) on the microstructure are established. The results of this work suggest that in the solidification processing of MMCs, it is important to optimize the process parameters both to avoid excessive interfacial reactions and simultaneously achieve wetting, so that a good particle distribution and interfacial bonding are obtained. The tensile properties, strain hardening, and fracture behavior of the AZ91/SiC composites are also studied and the results are compared with those of the unreinforced AZ91 alloy. The strengthening mechanisms for AZ91/SiC composite, based on the proposed SiC particle/matrix interaction during deformation, are used to explain the increased yield strength and elastic modulus of the composite over the magnesium matrix alloy. The low ductility found in the composites is due to the early appearance of localized damages, such as particle cracking, matrix cracking, and occasionally interface debonding, in the fracture process of the composite.

Mechanism of the early stages of α1 plate formation in a Cu-39 Pct Zn alloy

The early stages in the formation of α1 plates in the ordered β′ matrix of a Cu-39 pct Zn alloy have been studied with transmission electron microscopy (TEM). The early stage plates were found to be free of stacking faults. Their contrast features are indeed those normally expected from small coherent plates. Electron microdiffraction confirms that these plates have the 9R structure characteristic of α1 with the same lattice parameters and orientation relationships reported by previous investigators at much later stages of growth. Similarly, the 9R structure was disordered, even though it was formed in an ordered matrix, again repeating previous results obtained at a later stage of growth. These results further support the view that the α1 Cu-Zn plates form by a diffusion-controlled mechanism.

Heat flux transients at the casting/chill interface during solidification of aluminum base alloys

Heat flow at the metal/chill interface of bar-type castings of aluminum base alloys was modeled as a function of thermophysical properties of the chill material and its thickness. Experimental setup for casting square bars of Al-13.2 pct Si eutectic and Al-3 pet Cu-4.5 pct Si long freezing range alloys with chill at one end exposed to ambient conditions was fabricated. Experiments were carried out for different metal/chill combinations with and without coatings. The thermal history at nodal locations in the chill obtained during the experiments was used to estimate the interface heat flux by solving a one-dimensional Fourier heat conduction equation inversely. Using the data on transient heat flux q, the heat flow at the casting/chill interface was modeled in two steps: (1) The peak in the heat flux curve qmax was modeled as a power function of the ratio of the chill thickness d to its thermal diffusivity a, and (2) the factor (q/qmax) X α0.05 was also modeled as a power function of the time after the solidification set in. The model was validated for Cu-10 pct Sn -2 pct Zn alloy chill and Al-13.2 pct Si and Al-3 pct Cu-4.5 pct Si as the casting alloys. The heat flux values estimated using the model were used as one of the boundary conditions for solidification simulation of the test casting. The experimental and simulated temperature distributions inside the casting were found to be in good agreement.

Creep transitions in an Al-Zn alloy

The creep behavior of an Al-10 at. pct Zn alloy was investigated at temperatures in the range 573 to 800 K and in a normalized shear stress range, τ/G, extending from 10•6 to 10•3, where τ is the applied shear stress andG is the shear modulus. The results reveal the presence of four deformation regions: region I (very low stresses), region II (low stresses), region III (intermediate stresses), and region IV (high stresses). In regions II and III, the creep characteristics including the stress exponent, the shape of the creep curve, and the nature of creep transients after stress reductions are consistent with dislocation climb and viscous glide, respectively. The experimental transition stresses between region II (climb) and region III (glide) were compared with those predicted from the deformation criterion for solid-solution alloys, and it is demonstrated that the correlation between experiment and prediction becomes satisfactory when corrections concerning the appropriate diffusion coefficients for describing glide-controlled creep and climb-controlled creep, the stacking fault energy of the alloy, and the contributions of Suzuki interaction and Fisher interaction to solute atom drag forces are incorporated in the analysis. Experimental data in region IV are not sufficient to unambiguously identify the rate process, but calculations show that the values of the transition stress between region III and region IV agree reasonably well with those of the critical stress for dislocation breakaway from a solute-atom atmosphere. The characteristics of deformation in region I are still under investigation.

Effects of fatigue on the GP zones in Al-Zn alloys

Small-angle X-ray scattering has been employed to study the stability of GP zones in two Al-Zn alloys during fatigue, in order to provide statistically sound information on this process. In a 5.3 at. pct Zn alloy containing l025 zones per m3 with an average diameter of 18 A, the normally sluggish coarsening was accelerated by fatigue at room temperature by factors of l06 to l07. No coarsening occurred for larger zones, except near a fatigue crack. Reverted samples aged rapidly during fatigue at room temperature, but in a reverted sample of Al-3.5 at. pct Zn cycled at 77 K no appreciable zone growth occurred. Upon warming this sample to room temperature (without any load) rapid clustering took place. These results imply that a vacancy fraction of 10-5 to l0-6 was produced by the fatigue, and this excess vacancy concentration appears to cause the growth during cycling at room temperature.

Surface relief produced by diffusion induced boundary migration in Cu-Zn

Experimental observations are presented that demonstrate that diffusion induced grain boundary migration in copper foils exposed to zinc vapor, from a Cu-15 pct Zn alloy, can be studied directly after treatment without etching. The general characteristics of migration are in accord with previous investigations, but novel changes in the surface topography are described. Pits were formed on the surface of areas swept by boundary migration; also, the surface was often converted into a series of corrugations. The formation of pits suggests that the grain boundary diffusivity of zinc exceeds that of copper. The corrugations are believed to indicate that boundaries sometimes move in an intermittent manner.