ZK60 Alloy Research Articles

Microstructure and Damping Capacity of ZK60 Alloy Sheets Fabricated by Twin Roll Casting and Hot Rolling Process

ZK60 magnesium alloy sheets with 0.65 mm thickness were successfully fabricated by twin roll casting (TRC) and subsequent hot rolling process. Fine equiaxed grains were obtained after T6 treatment by the short-term TRC and hot rolling process, and the grain size for different reduction ratio per pass was similar. The studied sheets exhibited high strength and elongation, and the tensile strength, yield strengths, and elongation for the 10% and 30% reduction per pass were above 400 MPa, 300 MPa, and 17.0 %, respectively. The damping capacity values at low strain decreased with increasing the reduction ration per pass and the values at high strain were similar for the different reduction ration per pass. The lower reduction ratio per pass and the heat treatment between rolling passes can improve the mobility of dislocations, which indicated that this process was beneficial for improving damping capacity. Compared with higher reduction ratio per pass, the high tensile properties and damping capacity were obtained by 10% reduction per pass hot rolling process.

The Effect of High‐Pressure Torsion on Microstructure, Hardness and Corrosion Behavior for Pure Magnesium and Different Magnesium Alloys

Severe plastic deformation by high pressure torsion (HPT) is used to process and refine the grain structure of commercial purity magnesium and AZ31, AZ91, and ZK60 magnesium alloys. Transmission electron microscopy shows that the microstructure of pure magnesium is characterized by a bi‐modal grain size distribution with grains in the range of a few microns and ultrafine grains after HPT, whereas the magnesium alloys display a homogeneous ultrafine grain structure after processing. X ray diffraction analysis reveals that the AZ91 alloy displays the largest lattice microstrain and this alloy also exhibits the highest hardness after processing. The processed AZ31 and the ZK60 alloys show similar microstructures and maximum values of hardness. Contrary to earlier reports of significant improvements in the corrosion resistance of magnesium alloys in biological environments, the present results show that processing by HPT has no significant effect on the corrosion behavior of magnesium alloys in a 3.5% NaCl solution. By contrast, pure magnesium exhibits an increased corrosion resistance after HPT.

Effect of electropulsing treatment on static recrystallization behavior of cold-rolled magnesium alloy ZK60 with different reductions

Effect of electropulsing treatment (EPT) on recrystallization behavior of cold-rolled Mg alloy ZK60 strips was investigated. It was found that EPT significantly improved nucleation rate and migration ability of grain boundaries, leading to accelerated recrystallization of the deformed metals at relatively low temperature. After the recrystallization induced by EPT, the average grain size of 20% rolling reduction samples decreased from 113 μm to around 10 μm, meanwhile the typical basal-type texture of the cold-rolled sample was weakened. EPT was normally accompanied with a thermal and an athermal effects. The athermal effect played a dominated role in increasing nucleation rate, while the thermal effect promoted grain growth. A fewer recrystallized grains originated along the grain boundaries in the 10% reduction samples, while most of the recrystallization took place inside the twins in the 20% reduction samples.

Impression creep behavior of extruded ZK60 and ZK60+1 %Y magnesium alloys

Abstract The creep behavior of the extruded Mg alloys ZK60 and ZK60+1 %Y was investigated by means of the impression creep technique. The tests were carried out at a temperature in the range of 175–225 °C and under punching stress in the range of 25–100 MPa. The results showed that a 1 wt.-% yttrium addition could improve the creep resistance of ZK60. The creep mechanism of the extruded Mg alloy ZK60 consists of grain boundary diffusion by grain boundary sliding and that of the extruded Mg alloy ZK60+1 %Y grain boundary slip initiated by Mg. The microstructure of the extruded Mg alloy ZK60 consists mainly of the Mg phase and that of the Mg alloy ZK60+1 %Y in the extruded condition is composed of an α-Mg matrix and β-Mg3Zn3Y2 phase. After the press-in creep, the extruded Mg alloy ZK60 precipitates MgZn2 and MgZn phases and a small amount of the Zr-Zn phase, and the extruded Mg alloy ZK60+1 %Y precipitates MgZn2, MgZn, Y-Zn and the rare earth phase Mg-Y. The precipitation of the rare earth phase is represented by a discontinuous thin strip and a fine granular uniform distribution in the matrix. The precipitation of the rare earth compound phase shows high thermal stability, which can improve the creep resistance of the alloy. The Y-containing alloy ZK60 manifests higher threshold stress and better creep resistance due to the formation of the rare earth thermally stable particle.

Lanthanum-Containing Magnesium Alloy with Antitumor Function Based on Increased Reactive Oxygen Species

Developing antitumor implants is of great significance to repair tumor-induced bone defects and simultaneously prevent bone tumor recurrence. The tumor cells, compared to normal cells, have a high reactive oxygen species level. They are vulnerable to oxidative insults under increased intrinsic oxidative stress. The lanthanum (La) ion with high phospholipid binding ability can open the mitochondrial permeability transition pore, which blocks the electron transport chain in the mitochondria, and consequently increases reactive oxygen species level. In this study, La was alloyed to Mg-6Zn-0.5Zr (ZK60) through selective laser melting technology. The results indicated that the mitochondrial membrane potential dropped whilst the reactive oxygen species increased as the La content increased. ZK60-1.0La revealed a high cell inhibition rate of 61.9% for bone tumor cell and high cell viability of 91.9% for normal cells, indicating that the alloy could induce bone tumor cell death, as well as exhibit good biocompatibility for normal cell. In addition, its degradation rate 1.23 mm/year was lower than that of ZK60 alloy 2.13 mm/year, which was mainly attributed to the grain refinement.

Effect of Compressive Deformation on Wear Property of Extruded ZK60 Magnesium Alloy

The present study investigates the dry sliding wear behavior of precompressed ZK60 alloy using a ball-on-disc wear test machine under normal loads of 20 and 40N at a sliding speed of 0.5m s−1 for a constant sliding distance of 1,500m. Microstructures and worn surfaces were characterized by optical microscopy and scanning electron microscopy. Microhardness measurements were taken to evaluate mechanical properties. Results showed that both the microhardness and wear resistance of uncompressived alloy can be improved with precompression. This is attributed to the grain refinement via subdivision of twin lamellae generated by compressive deformation. Furthermore, the worn surface studies showed a mixed type of wear mechanisms: oxidative and delamination wear took place under higher applied loads.

Grain Refinement by Second Phase Particles under Applied Stress in ZK60 Mg Alloy with Y through Phase Field Simulation.

Based on the principle of grain refinement caused by the second-phase particles, a phase field model was built to describe the recrystallization process in the ZK60 alloy system with Y added under applied stress between temperatures 573 and 673 K for 140 min duration. The simulation of grain growth with second phase particles and applied stress during annealing process on industrial scale on the condition of real time-space was achieved. Quantitative analysis was carried out and some useful laws were revealed in ZK60 alloy system. The second phase particles had a promoting effect on the grain refinement, however the effect weakened significantly when the content exceeded 1.5%. Our simulation results reveal the existence of a critical range of second phase particle size of 0.3–0.4 μm, within which a microstructure of fine grains can be obtained. Applied stress increased the grain coarsening rate significantly when the stress was more than 135 MPa. The critical size of the second phase particles was 0.4–0.75 μm when the applied stress was 135 MPa. Finally, a microstructure with a grain size of 11.8–13.8 μm on average could be obtained when the second phase particles had a content of 1.5% and a size of 0.4–0.75 μm with an applied stress less than 135 Mpa after 30 min annealing at 573 K.

Degradation Behavior of Micro-Arc Oxidized ZK60 Magnesium Alloy in a Simulated Body Fluid

Bio-ceramic coatings were synthesized on ZK60 magnesium alloys by micro-arc oxidation (MAO). The degradation behavior of the ZK60 alloys with and without MAO coating in the simulated body fluid (SBF) was studied. The samples were characterized by means of scanning electron microscopy (SEM), laser scanning confocal microscopy (CLSM), and X-ray diffraction (XRD). Electrochemical impedance spectroscopy (EIS) was used to study the degradation behavior. The results showed that the porous MAO coating mainly consisted of MgO, Mg2SiO4, Mg3(PO4)2, and CaCO3. The pH values of both coated and uncoated samples increased over time. However, the pH values of the SBF for coated samples always maintained a lower level compared with those for the uncoated samples. Thereby, the coated samples showed a much lower degradation rate. After immersion in SBF for 5 days, corrosion product containing Ca and P was found on both samples, while the deposition was more active on the coated samples. The degradation models for the uncoated and coated samples in the SBF are also proposed and discussed.

Reducing the tension-compression yield asymmetry in an extruded ZK60 alloy by ultrafine grains

Ultrafine-grained ZK60 alloys were successfully fabricated by powder metallurgy followed by hot extrusion at different temperatures. The effects of the texture changes of ultrafine-grained ZK60 magnesium alloy on the asymmetry of tension-compression yield under different extrusion temperatures, and the relation between texture evolution and mechanical properties of the alloys during axial tension-compression deformation were studied. The results show that, in the ultrafine-grained ZK60 alloy, the initial texture of the alloy is a weak (0002) basal fiber texture. As the extrusion temperature increases from 523 to 623 K, the fibrous texture of the base material is weakened, and the tension-compression yield asymmetry is depressed from 1.1 to 1.0. During axial tensile deformation, twinning is not activated. With increasing tensile strain, no significant rotation of crystal grains occurs, and the stress remains stable until tensile fracture occurs. In the early stage of axial compression yield, no significant rotation of crystal grains occurs. As the compressive strain increases until the end of the compressive strain, the (0002) basal plane of the crystal grains rotates in a direction approximately perpendicular to the compression axis. At this point, the grain orientation factor is low, and the slip system is still in a hard orientation and is inhibited by the ultrafine grains. Twinning is difficult to start, so that the strain hardening rate rises rapidly until compression fracture occurs. Therefore, the weak extruding fiber texture of the basal plane and the ultrafine-grained structure both determine the deformation mechanism of ZK60 alloys at room temperature during axial tension and compression deformation, thereby significantly depressing the axial tension-compression asymmetry of ZK60 alloys.

Study on Porous Mg-Zn-Zr ZK61 Alloys Produced by Laser Additive Manufacturing

This study reports the effect of Zn contents on surface morphology, porosity, microstructure and mechanical properties of laser additive manufacturing (LAM) porous ZK61 alloys. The surface morphology and porosity of the LAMed porous ZK61 alloys depend on the laser energy input. With increasing Zn contents, the surface quality of porous Mg-Zn-Zr alloys became worse, the grains are obviously refined and the precipitated phases experienced successive transitions: MgZn → MgZn + Mg7Zn3 → Mg7Zn3. The microhardness was improved significantly and ranged from 57.67 HV to 109.36 HV, which was ascribed to the fine grain strengthening, solid solution strengthening and precipitation strengthening. The LAMed porous Mg-15 wt.% Zn-0.3 wt.% Zr alloy exhibits the highest ultimate compressive strength (73.07 MPa) and elastic modulus (1.785 GPa).

Microstructure and Corrosion Properties of ZK60 Alloys Modified by Micro-Arc Oxidation Coatings Using Phosphate-Borate Electrolyte in KOH Solution

Microstructure and Corrosion Properties of ZK60 Alloys Modified by Micro-Arc Oxidation Coatings Using Phosphate-Borate Electrolyte in KOH Solution

Effects of friction stir processing on hydrogen storage of ZK60 alloy

In this paper we report the use of a novel processing route to produce samples for use as a hydrogen carrier. ZK60 alloy was produced by induction melting and sheets taken from the melt ingot were submitted to Friction Stir Processing (FSP) and subsequent manual filing with a rasp under ambient conditions. Samples from the Base Metal As-Cast (AC) and Stir Zone (SZ) were microstructurally investigated before and after filing including the alloy in as-cast state. The results showed that before filing SZ and AC samples presented equiaxial grains with the SZ sample having a much finer microstructure compared to AC. The values of grain sizes are around 150 μm and 1–2 μm for the AC and SZ samples, respectively. After filing, both samples presented similar grain sizes of only 60 nm. Although they attained similar grain sizes, the filings from SZ were more homogeneous and presented thinner innerlayers compared to its AC counterpart. The filings taken out from the SZ presented much faster kinetics for hydrogen absorption mainly due to its thinner innerlayers and its finer second-phase particle distribution, reaching up to 4.5 wt% of hydrogen uptake against only 1.0 wt% for AC sample after 10 h of absorption in the first cycle. Both samples presented similar behavior for full discharge time. These results show the possibility of using FSP with subsequent filing as a mean to obtain materials with suitable properties for use as energy carriers with enhanced kinetics and better oxidation resistance in shorter processing times.

On the Influence of Solution and Ageing Treatments on the Microstructure of ZK40 Alloys Modified with Ca, Gd, Nd and Y Additions

Abstract As-cast ZK40 alloys, modified with the addition of CaO, Gd, Nd and Y were investigated. Solution heat treatments were performed based on differential thermal analysis results. The unmodified ZK40 alloy exhibited microstructure with nearly no intermetallic compound but with precipitates formed during the solution treatment. The modified ZK40 alloys exhibited a semi-dissolved network of intermetallic compounds along the grain boundaries and zones of intermetallic compounds within the grains. Interestingly, no precipitates were observed immediately next to the grain boundaries. The energy dispersive X-ray spectroscopy line scans showed an enrichment of Zn and Zr in the regions where the precipitates are found, suggesting that they are Zn-Zr precipitates. The ageing behaviour was compared between the as-cast and the solution treated materials and it was found that apart from the ZK40-Gd, ZK40-Nd and ZK40-Y aged at 200 °C after solution treatment, there is no notable ageing response for the investigated alloys.

Influence of Intermetallic Particles on the Corrosion Properties of Extruded ZK60 Mg Alloy Containing Cu

The microstructure and corrosion behavior of the extruded ZK60 Mg alloys with different Cu content were comparatively investigated. The ZK60 alloy had a microstructure consisting of α-Mg grains with intermetallic MgZn2 and Zn2Zr3 particles. The addition of 1 wt % Cu resulted in the additional presence of CuMgZn particles. In a 0.6 M NaCl solution at 25 °C, the corrosion rate of the alloy with the added Cu appeared to be about 16% faster than that of the alloy without the addition of Cu. The factors affecting the degraded corrosion resistance of the Cu-added ZK60 alloy are discussed.

Effect of La content and extrusion temperature on microstructure, texture and mechanical properties of Mg-Zn-Zr magnesium alloy

The microstructure, texture and mechanical properties of Mg-6wt%Zn-0.5 wt%Zr (ZK60) alloys with different La contents (0, 0.5 and 1 wt%) were investigated. The alloys were produced by low-pressure die casting and extruded at 300 °C and 400 °C, following homogenization at 400 °C for 24 h. La addition to ZK60 alloy resulted in a formation of Mg-Zn-La ternary phase, generating a semi-continuous network structure in their as-cast state. After extrusion, secondary phases were broken into fine particles distributed along the extrusion direction. These fragmented particles led to a nucleation of new grains around them i.e. particle stimulated nucleation (PSN), and promoted dynamic recrystallization (DRX) during extrusion. Therefore, increasing La content led to an increase in DRX fraction. Higher extrusion temperature resulted in larger DRXed grains and higher DRX fraction. The basal texture intensity was also decreased with increasing La addition and extrusion temperature by PSN mechanism and solute atoms of La. The ZK60-1La alloy extruded at 300 °C showed a superior yield strength of 311 MPa and ultimate tensile strength of 360 MPa as a result of significant grain refinement and dispersion strengthening. Increasing extrusion temperature resulted in a decrease in yield and ultimate tensile strengths and increase in ductility.

Very-high-cycle fatigue crack initiation and propagation behaviours of magnesium alloy ZK60

ABSTRACTThe aim of this paper is to assess the very-high-cycle fatigue (VHCF) behaviour of a magnesium alloy (ZK60). Results indicate that the fatigue crack initiates from an area consisting of many distributed facets, while the region of early crack propagation is characterised by parallel traces, based on a fractographic analysis. The significant differences in morphology around the crack initiation area result from the interaction between the deformation twinning and the plastic zone at the crack tip. In addition, the fatigue crack propagation rate around the crack initiation site is also estimated based on a modified Murakami model. It is found that the formation stage for the fatigue crack is of great importance to the fatigue failure mechanism in the VHCF regime.

Bimodal grain microstructure development during hot compression of a cast-homogenized Mg-Zn-Zr alloy

Hot deformation of a cast-homogenized ZK60 alloy was studied by compression at a temperature of 450 °C and a strain rate of 0.001 s−1 to investigate microstructural evolution. The deformed microstructure was characterized using electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM). EBSD observations of the deformed microstructure showed that hot deformation of this alloy resulted in a bimodal grain microstructure consisting of large pancaked unrecrystallized dendrites surrounded by recrystallized equiaxed fine grains. HRTEM studies revealed the presence of nano-(Zn-Zr)-precipitates in the deformed microstructure. Due to the coherency of precipitates/matrix, the dislocations were pinned by the nano-precipitates inside the unrecrystallized grains and the dislocation motion inside the grains was impeded, hence, a substructure evolved. Consequently, dynamic recrystallization (DRX) was suppressed and deformation was concentrated inside the DRXed region.

An insight into the effect of buffer layer on the electrochemical performance of MgF2 coated magnesium alloy ZK60

Magnesium (Mg) has emerged as potential implant material owing to its property of biodegradation. The roadblock to the commercial use of Mg as implant material is its fast degradation in body fluids. The degradation of the Mg and its alloys can be retarded by surface coatings. In this work, the potential of MgF2 coating on the surface of Mg alloy ZK60 (Mg-6.9Zn-0.8Zr) was evaluated for its corrosion properties. Two-step chemical conversion process was used to coat MgF2 on the surface of ZK60 alloy. In the first step, a secondary layer of Mg(OH)2 was introduced by boiling the samples in NaOH solution. In the second step, these samples were immersed in hydrofluoric acid to obtain MgF2 coating. SEM, IR Spectroscopy, and XRD were employed to confirm the formation of Mg(OH)2 and MgF2. The wettability tests showed an increase in surface hydrophobicity as a result of conversion treatment. The potentiodynamic polarization tests exhibited an improvement in the corrosion potential from −1.52 V vs. SCE to −1.49 V vs. SCE after two-step conversion treatment. Moreover, coated sample witnessed a noticeable drop in hydrogen evolution compared to untreated ZK60. For a better insight, the results were compared to the MgF2 coatings achieved on the surface of ZK60 without any buffer layer. The coating of MgF2 with a buffer layer of Mg(OH)2 on the surface of ZK60 exhibited a noble corrosion potential, controlled degradation, and nominal hydrogen evolution compared to the untreated ZK60.

Flow and fracture study for ZK60 alloy at dynamic strain rates and different loading states

This paper presents an on-going study of light-weight alloy ZK60 magnesium. The uniaxial tensile tests were carried out with strain rate range of (0.0001–1000)/s−1 and with different stress states. Elemental data was identified through an iteration process using finite element analysis. The modified Johnson-Cook (J-C) model was calibrated to describe the flow stress as a function of strain and strain rate. The modified Mohr-Coulomb (M-C) model, considering the effects of strain, stress state and strain rate, was proposed with satisfactorily determined parameters. Compared by the original J-C fracture model, the modified M-C fracture model tracks the fracture behavior more accurately. To complement the macroscale fracture information, fractography reveals the fracture and deformation mechanism in microscale. The agreements between the simulations and tests further confirmed that the modified J-C material model and the modified M-C material model can give a precise estimate of the mechanical and fractural behavior of the ZK60 alloy.

Corrosion behaviour of as-cast ZK40 with CaO and Y additions

Abstract The microstructures of as-cast ZK40, ZK40 with 2% (mass fraction) CaO and ZK40 with 1% (mass fraction) Y were investigated, and the intermetallic phase morphology and the distribution were characterised. By having discrete intermetallic particles at the grain boundaries for the ZK40, the microstructure was modified to a semi-continuous network of intermetallic compounds along the grain boundaries for the ZK40 with CaO or Y additions. The CaO was not found in the microstructure. However, Ca was present in Ca2Mg6Zn3 intermetallic compounds which were formed during casting. Hydrogen evolution and electrochemical impedance spectroscopy tests revealed that the addition of CaO slightly enhanced the corrosion resistance whereas Y had a negative effect on the corrosion resistance of ZK40. Immersion tests showed that severe localised corrosion as well as corrosion along the intermetallic compounds played an important role in the corrosion process of ZK40–Y whereas the localised corrosion was not pronounced for ZK40 or ZK40–CaO alloys. Micro-segregation in the α-Mg matrix was notably higher for the ZK40 alloy compared with the modified alloys. The combination of this effect with a possible formation of a more stable corrosion layer for the ZK40–CaO was attributed as the main reason for an improved corrosion resistance for the ZK40–CaO alloy.