ZK60A Alloy Research Articles

Effect of Graphene Oxide as an Anodizing Additive for the ZK60A Magnesium Alloy: Correlating Corrosion Resistance, Surface Chemistry and Film Morphology

The aim of the present work was to study the effect of graphene oxide as an additive in the anodization bath of the ZK60A magnesium alloy on the corrosion resistance, film morphology and surface chemical composition. The anodizing process was conducted at a constant current density of 30 mA.cm−2 in an electrolyte consisting of 3 M de KOH, 0.15 M de Na2SiO3 and 0.1 M Na2B4O7.10H2O. Graphene oxide was added to this bath at three different concentrations: 0.5 g.L−1, 1.0 g.L−1 and 3.0 g.L−1. The ability of the graphene oxide nanofiller to enhance the corrosion resistance of the ZK60A alloy was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization tests in 3.5 wt.% NaCl solution. The surface chemical composition was assessed by X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) coupled with EDS analysis was employed to examine the anodized layer morphology and thickness. The results pointed to a beneficial effect of graphene oxide addition on the corrosion resistance of the anodized ZK60A which was dependent on the concentration of the nanofiller in the anodizing electrolyte.

Influence of ECAP Processing and Heat Treatment on Tensile Property and Fatigue Crack Initiation in ZK60A Alloy

Influence of ECAP Processing and Heat Treatment on Tensile Property and Fatigue Crack Initiation in ZK60A Alloy

Effect of microalloying with Ca and Al on the microstructure, mechanical and corrosion properties of the ZM60 alloy

The microstructure, mechanical and corrosion properties of the ZM60 alloy with different contents of Al and Ca were investigated by optical microscopy(OM), x-ray diffraction(XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tensile tests. The results show that the as-cast ZM60 alloy consisted of α-Mg and Mg51Zn20 phases. There is no obvious change of microstructure when adding 1 wt% of Al to the ZM60 alloy. With the increasing addition of Al, Mg32(Al,Zn)49 phase presented in the alloy replacing the Mg51Zn20 phase. The microstructure of the as-cast alloy in which Ca and Al were simultaneously added was composed of α-Mg, Al8Mn5and Mg32(AlZn)49 phases. The grain size of the extruded alloys were well refined with the addition of Al or a mixture of Al and Ca. The grain refining effect of adding Al and Ca is better than adding Al alone, leading to the smallest grain size of2.2 μm. The strengthening mechanism of the alloys were mainly fine-grain strengthening with the addition of Al and Ca. Compared with the ZK60A alloy, the tensile strength of the ZAMX6100 alloy increased by about 20MPa, the yield strength increased by about 30MPa, and the elongation was similar. The corrosion resistance of Mg-6Zn alloy was also improved significantly through adding Al and Ca.

Influence of ECAP Processing on Fatigue Crack Nucleation on ZK60A Magnesium Alloy

Low-cycle fatigue tests were conducted on ZK60A magnesium alloy that were processed by equal-channel angular pressing (ECAP) method. The ECAP processing was carried out on a hot-extruded ZK60A alloy at a die temperature of 473K. Total pass number was four and the processing route was Route Bc. One of the ECAPed sample was annealed at 573K to induce grain coarsening. The low-cycle fatigue tests were conducted under a constant plastic strain amplitude of εpl=2×10-3, in air at room temperature. A hysteresis loop shape during the low-cycle fatigue tests depended on the sample: a tension-compression asymmetric shape was recorded in the as-drawn specimen having the tensile axis parallel to the extruction direction, while a symetric shape was seen in case of the tensile axis perpendicular to the extrusion direction. Deformation twinning during fatigue was most probably attribute to the asymmetric hysteresis loop shape. Because the asymmetric hysteresis loop was absent in the ECAPed specimen, it is possible that grain refinement suppressed the deformation twinning in the fatigue test. In the as-drawin specimen having the tensile axis parallel to the extrusion direction, a small crack was observed near a deformation twin. By contrast, a fatigue crack in the as-ECAPed specimen was generated along a shear band that was inclined to the tensile axis at 45°. After the ECAPed specimen was annealed at 573K, an intense shear banding and a subsequent crack nucleation were moderated. Accordingly, it can be said that the low-temperature annealing on the ECAPed ZK60A magnesium alloy reduced the fatigue crack nucleation sites.

Evolution Of Precipitate Morphology During Extrusion In Mg ZK60A Alloy

Abstract In this study, a continuously casted ZK60A magnesium alloy (Mg-Zn-Zr) was extruded in two different extrusion ratios, 6:1 and 10:1. The evolution of precipitates was investigated on the two extruded materials and compared with that of as-casted material. The microstructural analysis was performed by electron backscatter diffraction and transmission electron microscopy, and the compositional information was obtained using energy-dispersive X-ray spectroscopy. Several distinct morphologies of precipitates were observed, such as dot, rod, and disk shaped. The formation mechanisms of those precipitates were discussed with respect to the heat and strain during the extrusion process.

High Temperature Deformation Flow Of A ZK60A Magnesium Alloy After Extrusion

AbstractFlow behavior of a ZK60A magnesium alloy after continuous casting and subsequent extrusion was examined in tension at a range of strain rates of 3.0×10−6− 1.0×10−2s−1at temperatures of 473-623K. The results demonstrated that the alloy exhibited a maximum elongation of ~250% at 523K when tested at an initial strain rate of 1.0×10−5s−1and strain rate sensitivity,m, of ~0.3-0.4 and the activation energy of ~94 kJ/mol were calculated under the testing conditions. The detailed investigation suggested that the high temperature flow of the ZK60A alloy having submicrometer grains demonstrates quasi-superplastic flow behavior controlled by a dislocation viscous glide process.

Hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy

The hot deformation behavior and workability of pre-extruded ZK60A magnesium alloy were investigated by compression tests in the temperature range of 250–450 °C and the strain rate range of 0.001–10 s−1. The constitutive equation for the pre-extruded ZK60A alloy can be described by hyperbolic sine function. Processing maps were constructed from true strains of −0.2 to −0.8. The alloy experienced complete dynamic recrystallization (DRX) and showed good workability in the temperature range of 300–400 °C and the strain rate range of 0.01–0.001 s−1, where hot working in pre-extruded ZK60A, such as forging, can be carried out. For large deformation to true strain of over −0.5, strain rates above 0.1 s−1 are not recommended at all temperatures, where flow instability such as local strain concentration, twinning deformation, abnormal grain growth, micro-cracks, and shear fracture were observed. Climb-controlled dislocation creep dominates both the plastic deformation and nucleation of DRX of the pre-extruded ZK60A magnesium alloy.

Evolution in hardness and texture of a ZK60A magnesium alloy processed by high-pressure torsion

A ZK60A magnesium alloy was processed by high-pressure torsion (HPT) at room temperature at compressive pressures up to a maximum of 6.0GPa for up to 5 revolutions and this produced significant grain refinement and the development of a bi-modal microstructure. The evolution of hardness was evaluated using measurements of the Vickers microhardness and the change in texture was examined by X-ray diffraction (XRD) analysis. The hardness results demonstrated an evolution with increasing equivalent strain and a strain hardening behavior which may be quantified using a hardenability exponent of ~0.07 when processing under a pressure of 6.0GPa. An XRD analysis over the total disk surface showed that the texture changed from a typical extrusion prior to HPT towards a saturated very weak basal fiber texture which developed in the early stages of HPT and remained constant with additional torsional straining up to 5 turns. By contrast, an XRD analysis of the local microstructure taken at the edges of the processed disks demonstrated significant changes towards a strong basal fiber texture via different texture stages with increasing HPT revolutions. This study demonstrates the importance of carefully documenting the measurement areas selected for texture analysis in the ZK60A alloy after HPT because of the occurrence of significant microstructural variations within the samples.

Comparison of Workability of ZK60A Alloy Depending on Casting Methods

In this research, the effect of casting methods on the workability of magnesium alloy ZK60A was investigated by comparing two different billets, fabricated by semi-continuous casting and die casting. To determine the workability of the materials, uniaxial compression tests were conducted at different elevated temperatures and strain rate of 0.01/s. In addition, the X-ray inspection system and electron backscatter diffraction (EBSD) were employed to compare their internal defects and microstructures, respectively. The workability of ZK60A depending on the casting methods is discussed based on the obtained experimental results.

Workability of ZK60A Alloy Depending on Microstructure

In this study, the variation of workability of semi-continuously casted and extruded ZK60A magnesium alloy was investigated. To determine the deformation capability of two different billets, uniaxial compression tests were conducted at elevated temperatures and two different strain rates. In addition, the microstructural evolution was investigated using electron backscatter diffraction (EBSD) to compare the microstructure before and after the extrusion. The formability of ZK60A depending on the microstructure is discussed based on the experimental results obtained in this study, and is compared with earlier research in the literature.

Mechanical and in vitro degradation behavior of ultrafine calcium polyphosphate reinforced magnesium-alloy composites

Magnesium alloy (ZK60A) matrix composites reinforced with 2.5, 5, 7.5 and 10 wt.% calcium polyphosphate particles, which were sphere-like in shape with average size of about 750 nm, were fabricated by powder metallurgy. The microstructure, mechanical properties and degradation behavior in physiological saline of the composites were investigated. The obtained results show that ultrafine calcium polyphosphate particles uniformly distribute in the ZK60A matrices without voids for the composites containing 2.5 and 5 wt.% calcium polyphosphate. For the composites containing 7.5 and 10 wt.% calcium polyphosphate, however, calcium polyphosphate particles agglomerate in the ZK60A matrices, and some obvious voids appear. The ultimate tensile strengths, yield strengths and elastic moduli of the composites tend to increase when the calcium polyphosphate contents increase from 0 to 5 wt.%, however, appear to decrease with the further increase of calcium polyphosphate from 5 to 10 wt.%. The weight losses of the composites, pH values and Mg ion concentrations of the solutions immersing the composites gradually decrease with increase of calcium polyphosphate content, which indicates that the addition of more calcium polyphosphate into ZK60A alloy results in significant degradation slow-up of the composites. This can be attributed to the formation of dense corrosion product layers on the composites. The composites have good mechanical properties and controllable degradation rates and thereby have potential to be used as load-bearing bone implants.

Increasing the mechanical properties of high damping woodceramics by infiltration with a magnesium alloy

Woodceramics are new porous ecomaterials and have been proved to possess good damping characteristics compared with other ceramics, but their mechanical properties have been found to be relatively poor. In order to achieve good mechanical properties and good damping properties simultaneously, a woodceramics/ZK60A (WCMs/ZK60A hereafter) composite is fabricated using high-pressure vacuum infiltration technique. Microstructural analysis as well as measurement of mechanical properties and damping behavior of WCMs/ZK60A composite is made. Experimental results show that ZK60A alloy has infiltrated most of the pores and WCMs/ZK60A composite has an obvious interpenetrating network structure. Its strength, Young's modulus and damping characteristics are all much higher than those of unreinforced woodceramics. The intrinsic damping of woodceramics and dislocation damping in matrix are proposed as the main contributors of the damping of WCMs/ZK60A composite at low temperature while Interface damping is likely to be responsible for the majority at elevated temperature.

Mechanical properties and damping behavior of woodceramics/ZK60A Mg alloy composite

The mechanical properties and damping behavior of Woodceramics/ZK60A (WCMs/ZK60A, hereafter) composite fabricated by liquid metal infiltration method have been investigated. Experimental results show that ZK60A alloy has infiltrated most of the pores and WCMs/ZK60A composite has an obvious 3-D interpenetrating network structure. Strength and Young’s modulus of the resultant composite are much higher than those of unreinforced woodceramics. Damping values of WCMs/ZK60A composite improve based on those of woodceramics and increase with testing temperature.

ＺＫ６０Ａマグネシウム合金すえ込み鍛造材の集合組織

Texture measurements were made of upsetting forged disk to 50 and 70% reduction from semi-continuously cast rod and extruded rod of ZK60A alloy having weak [1120] and strong [1010] fiber texture parallel to rod axes respectively. The method of Harris for inverse pole figures of fiber textures was used. To verify if the method is appropriate for measurement of forging texture in magnesium, texture in extruded plate of AZ31 alloy was also measured. Initial textures changed during upsetting gradually to [0001] orientation parallel to upsetting direction, sharpness of these fiber texture being more shape at surface layer on disk than inner layer and at higher reduction. Textures in various location in disk from cast bar were uniform in comparison with that from extruded rod in which upsetting direction are parallel to extrusion direction.