ZM21 Magnesium Alloy Research Articles

Erosion Wear Property of Surface Diffusion Alloyed Coatings on Magnesium Alloy

Erosion wear tests under different erosion slurry mediums were carried out to investigate erosion properties of the treated samples of ZM5 magnesium alloy by surface diffusion alloying processing (SDAP).The result indicated that the micro-hardness (HV172) near the surface of alloyed specimen was about twice more than that of its substrate(HV82) after treated at 390°C for 8h.The erosion wear resistance β (0.68×104 mm2/g) of the treated specimen was better than that of untreated specimen (0.48×104mm2/g) under the conditions of erosion slurry of oil and quartz. The difference of erosion wear resistance between them was primary due to cutting wear mechanism. While erosion mediums was changed to the slurry of water and quartz, the wear resistance β of the treated specimen increase up to 0.24×104 (mm2/g), and that of the untreated specimen was only 0.09×104 (mm2/g),the difference between them resulted from corrosion wear mechanism predominating, which worsen the erosion wear resistance β.

Evaluation of magnesium alloys with alternative surface finishing for the proliferation and chondro-differentiation of human mesenchymal stem cells

Articular cartilage has little capacity for self-repair. As a result, continuous mechanical stress can lead to the degradation of articular cartilage, culminating in progressive damage and joint degeneration. Tissue engineering has arisen as a promising therapeutic approach to cartilage repair. Magnesium alloys are one of the most important metallic biomaterials emerging in this area due to their biocompatibility, bio-absorbability and especially to their mechanical properties. These properties make magnesium alloys a promising biomaterial in the regeneration of cartilage tissue. Objective. This study was undertaken to analyze the influence of surface characteristics of magnesium alloys in the adhesion, proliferation and differentiation of human mesenchymal stem cells (MSCs). Methods. Two commercial magnesium alloys (AZ31B and ZM21) were subjected to different treatments in order to obtain four different surfaces in each alloy. Human MSCs were seeded into the magnesium alloys and analyzed for their proliferation and chondrogenesis differentiation ability. Results. Human MSCs showed a greater proliferation and chondro-differentiation when cultured in the ZM21 magnesium alloy with a surface finishing of fine sanding, polishing, and etching.

Friction stir welding of magnesium alloy ZM21

Friction stir butt welding of Mg-Zn-Mn alloy ZM21 hot rolled plates (in three thicknesses — 5 mm, 10 mm and 25 mm) was investigated. Defect-free, full-penetration welds were produced after careful process parameter optimization. Microstructural studies, hardness tests, tensile tests, and bend tests were carried out. Welds produced in 5 mm thick (5-mm-welds) and 10 mm thick plates (10-mm-welds) showed relatively finer grains in the weld nugget and in the heat-affected zone compared to the welds produced in 25 mm thick plates (25-mm-welds). When compared to the base material, 25-mm-welds showed coarser grains both in the weld nugget and in the heat-affected zone. No significant hardness differences were observed between the welds and the base material. Tensile tests on 5-mm and 10-mm-welds yielded a joint efficiency of more than 75%. Bend performance of the welds was found to be satisfactory, falling only slightly behind the base material. Overall, the results show that friction stir welding can be successfully utilized for joining magnesium alloy ZM21 in various thicknesses.

Ignition-proof mechanism of ZM5 magnesium alloy added with rare earth

The ignition-proof mechanism of ZM5 magnesium alloy added with 0.1% (mass fraction) rare earth (RE) was investigated. The oxide scales and substrates were characterized by scanning electronic microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and tensile test. And an oxidation model of ZM5 alloy with RE was established. The results show that the ignition temperature of ZM5 alloy is particularly elevated from 654 to 823 °C, the microstructure is refined, and the tensile strength is slightly improved from 168.2 to 174.6 MPa by adding 0.1% RE. A double-layer oxidation film formed on the alloy surface under high temperature mainly consists of MgO, RE2O3 and Al2O3, which is 2.5–3.5 μm in thickness. It is found that the forming of protective oxidation film on the thermodynamics is attributed to RE elements congregating on the surface of molten Mg alloy.

Comparison of Microstructure and Mechanical Properties between ZM21 and ZME210 with Different Hot Extrusion Ratios

The mechanical properties and microstructure of the as-extruded ZM21 magnesium alloy and its modified alloy ZME210 with addition of 0.35wt% cerium were investigated with different extrusion ratios from 14 to 182 by using mechanical property test, microscopic structure quantitative analysis, SEM observation and energy spectrum analysis. The results showed that both ZM21 and ZME210 had an extrusion ratio limit for grain refining, and the grains were found to be finer with higher extrusion ratio when the ratio was not higher than the limit value. The extrusion ratio limit for the best effect for grain refining of ZME210 is lower than that of ZM21. It was found that the Ce can refine the grains effectively after hot extrusion with different extrusion ratios. The effects of Ce on the microstructure and mechanical properties were analyzed.

Corrosion protection of magnesium alloy ZM21 by polyaniline-blended coatings

Phosphate-doped polyaniline pigment was prepared by a chemical oxidation method using ammonium persulfate in phosphoric acid media. Fourier transform infrared studies were done to characterize the pigment. The magnesium alloy ZM 21 was coated with polyaniline-pigmented paint, based on an epoxy binder, and the corrosion performance of the coating was studied by potential measurements and electrochemical impedance spectroscopy in 0.1% and 0.5% NaCl solutions. The results were compared with strontium chromate and filler material-pigmented coatings. It was found that the coating containing polyaniline provided similar protection for the magnesium alloy as that offered by chromate-pigmented paint.

Magnesium tube hydroforming

AbstractMagnesium alloys reveal a good strength‐to‐weight ratio in the family of lightweight metals and gains potential to provide up to 30 % mass savings compared to aluminium and up to 75 % compared to steel. The use of sheet magnesium alloys for auto body applications is however limited due to the relatively low formability at room temperature.Within the scope of this paper, extruded magnesium tubes, which are suitable for hydroforming applications, have been investigated. Results obtained at room temperature using magnesium AZ31 tubes show that circumferential strains are limited to a maximal value of 4 %. In order to examine the influence of the forming temperature on tube formability, investigations have been carried out with a new die set for hot internal high pressure (IHP) forming at temperatures up to 400 °C. Earlier investigations with magnesium AZ31 tubes have shown that fractures occur along the welding line at tubes extruded over a spider die, whereby a non‐uniform expansion at bursting with an elongation value of 24 % can be observed. A maximum circumferential strain of approx. 60 % could be attained when seamless, mechanically pre‐expanded and annealed tubes of the same alloy have been used. The effect of annealing time on materials forming properties shows a fine grained structure for sufficient annealing times as well as deterioration with a large increase at same time. Hence, seamless ZM21 tubes have been used in the current investigations. With these tubes, an increased tensile fracture strain of 116 % at 350 °C is observed as against 19 % at 20 °C, obtained by tensile testing of milled specimens from the extruded tubes. This behaviour is also seen under the condition of tool contact during the IHP forming process. To determine the maximum circumferential strain at different forming temperatures and strain rates, the tubes are initially bulged in a die with square cross‐section under plane stress conditions. Thereafter, the tubes are calibrated by using an optimised pressure‐time curve. The IHP forming process has also been used to demonstrate practicability and feasibility for real parts by manufacturing a technology‐demonstrator part using the magnesium alloy ZM21.

Hot Workability and Constitutive Equations of ZM21 Magnesium Alloy

One of the most challenging activities for magnesium industry is to increase productivity by introducing cost-effective processes. While die-cast magnesium alloys are in worldwide use, even in the demanding sector of automotive industry, where cost is the major asset, wrought magnesium alloys still not widely available. The aim of the present study was to evaluate the high temperature response by torsion testing of a ZM21 alloy, to calculate the constitutive equations to be used in FEM simulation of the extrusion process. The ZM21 alloy that was considered in the present study was Direct-Chill casted by Alubin Ltd., Israel. Torsion tests were carried out in air on a computer-controlled torsion machine, under strain rates ranging from 10-2 to 5 s-1 and temperatures from 200 to 400°C. The equivalent peak flow stress was related to temperature and strain rate by means of the conventional power-law and by the sinh equation. The microstructure of the alloy, even at 300°C, appeared largely unrecrystallized, with elongated grains; also at 400°C, the structure is more equiaxed, but elongated structures still appears.

镁合金表面激光熔覆纳米三氧化二铝

镁合金表面激光熔覆纳米三氧化二铝

Laser cladding of Al + Ir powders on ZM5 magnesium base alloy

Laser cladding of preplaced Al + Ir powders on a ZM5 magnesium alloy was performed to enhance the corrosion resistance of the ZM5 magnesium alloy. A metallurgical bond was obtained at the coating/substrate interface. The corrosion potential ( E corr) of the laser cladded sample was 169 mV positive to that of the untreated ZM5 substrate, while the corrosion current ( I corr) was some one order of magnitude lower. The laser cladded sample, unlike the untreated ZM5 substrate, showed a passive region in the polarization plot. Immersion tests confirmed that the corrosion resistance of the laser cladded ZM5 sample was significantly enhanced in 3.5 wt.% NaCl solution. The Al-rich phases of AlIr, Mg 17Al 12, and Al formed in the cladding layer and the rapid solid characteristics were contributed to the improved corrosion behavior of the coating.

Laser cladding of Mg20Al80 powder on ZM5 magnesium alloy

Laser surface engineering can be used to alter the surface of alloys and produce a fine microstructure, usually improving the corrosion resistance and wear resistance. In the present paper, a CO2 laser was used to melt preplaced Mg20Al80 powder with the objective of improving the corrosion resistance of ZM5 magnesium alloy in sea water solution. The corrosion behaviour of the ZM5 substrate and the laser cladding Mg20Al80 sample was studied with relating to their microstructures. Corrosion was studied in a 3·5 wt-%NaCl solution at pH 7 by observing the corrosion morphology. The results showed that the Mg17Al12 acted as galvanic cathode in both the ZM5 substrate and the cladding layer. The enhanced corrosion resistance was attributed to the fine dispersion of intermetallic phases and extended Al solid solutions by laser rapid solidification.

Evaluation of electrochemical and surface characteristics of conversion coatings on ZM21 magnesium alloy

Surface of a metal or material is important and suitable modification of the surface can provide enhanced properties for different applications. Magnesium is the lightest of all structural metals. Its low density (1·8 g cc−1 in alloy form) coupled with favourable casting properties, makes magnesium the material of choice for light weight components. But the metal is chemically highly reactive and prone to corrosion. Hence modification of the surface is important. The magnesium alloy under consideration is Mg–Zn–Mn, (ZM21) alloy system, and the composition is 2·03Zn–0·81Mn over which phosphate–permanganate, chromate conversion coatings were applied. The samples were subjected to surface roughness measurements, salt spray exposure tests, electrochemical potentiostatic polarisation studies in corrosive environment such as NaCl, NaOH, Na2SO4, NaHCO3 and NH4NO3. Microstructural examination, SEM analysis (for surface morphology), Fourier transform infrared (FTIR) spectral investigation (for determining the functional group) and X-ray diffraction (XRD) measurements (for identifying the compound) have also been employed for assessing the surface characteristics of this alloy. The results, in general, indicate that coatings provide enhanced corrosion resistance. Scanning electron microscopy of chromate conversion coating on ZM21 Mg alloy shows an intense transgranular crack on the coated film surrounded by a scattered distribution of spongy nature of film product. Scanning electron microscopy of phosphate conversion coating on ZM21 Mg alloy reveals a complete coverage showing a dense population and continuous network of film product. The formation of bonds among phosphorous, oxygen and hydrogen elements was shown by FTIR studies. X-ray diffraction analysis revealed the formation of compounds such as MgMnO3, Mg(OH)2, Mg2H, HPO4 in phosphate–permanganate conversion coated alloy, and compounds such as ZnCr2O4, Cr–O, CrO2, MnCrO3 in chromate conversion coating.

Study on Microstructure and Properties of Mg-9Al-xZn Alloys

Some Zn and a little Ag are added into ZM5 magnesium alloy (one of Mg-9 wt%Al-1 wt%Zn alloys in China), and the differences of the microstructures and properties between the new alloy and ZM5 is investigated. Effects of heat treatment and alloying elements (Zn and Ag) on the microstructure and tensile properties of Mg-9Al-xZn alloys, and relationships between the chemical composition, microstructure and properties are investigated. Zn ad Ag have obvious solid solution strengthening effects on Mg-9Al-xZn alloy, while Ag is detrimental to the corrosion resistance after being artificial aged. The morphology of pearlite-like secondary γ(Mg17Al12) phase (γII) has close relation with the properties.

The effect of solid diffusion surface alloying on properties of ZM5 magnesium alloy

In this research, solid diffusion process was used to form a diffusion alloying layer on the surface of ZM5 magnesium alloy to improve corrosion and wear resistance. It is shown that the solid diffusion layer was mainly composed of Mg–Al–Zn intermetallic compounds and Mg–Al–Zn solid solution transition zone that had more Zn and Al elements than untreated ZM5 magnesium substrate. The continued immersion test in 3% NaCl solution displayed that the diffusion-treated specimen had better corrosion resistance compared to the untreated ZM5 specimen. The polarization test indicated that the Mg–Al–Zn intermetallic compounds of the diffusion alloying layer were an effective corrosion barrier to decrease the corrosion rate for ZM5 magnesium alloy when exposed to 3% NaCl solutions. In addition, the microhardness values of the Mg–Al–Zn intermetallic compounds were much higher than those of the substrate and this would greatly contribute to the enhancement of wear resistance.

Uniaxial tensile behaviour of ZM-21 magnesium alloy at room temperature

Experiments were carried out to generate data on the uniaxial tensile forming of hot rolled ZM-21 magnesium alloy using a Hounsefield tensometer. During the experimental investigation at three different orientations namely rolling, transverse and thickness directions, the magnesium alloy was found to show increase in flow stress with respect to increasing amount of axial strain or deformation. Further, it was noted that the strain hardening index value for the thickness direction beyond the axial strain value of 0.08 is high while comparing the results obtained from other two directions. The plastic strain ratio value for directions namely rolling and transverse was observed to be very high for low strain value (less than strain value of 0.02) and low for high strain value. The ratio of true stress value at rolling direction to the true stress value at transverse direction was almost the same up to the axial strain value of 0.06 and then decreased with increasing axial strain value.

A study on barrelling in magnesium alloy solid cylinders during cold upset forming

Experiments were carried out to generate data on the upset forming of circular solid cylinders of hot-rolled magnesium alloy ZM-21. During the experimental investigation, the magnesium alloy cylinders were observed to show a change from a circular contact area on the top and bottom surfaces to an elliptical surface area. Calculations were made on the assumptions that the curvature of the barrel surface followed the geometry of both circular and elliptical arcs. It was observed that the measured radius of curvature of the barrel exhibited a straight-line relationship with a new geometrical shape factor, irrespective of the orientations, i.e., irrespective of whether the specimens were machined in the rolling, transverse or thickness direction of the hot-rolled plate. Further, empirical relationships were found to exist between the measured radius of curvature of the barrel and other variables such as the hydrostatic stress and the stress-ratio parameter.

Friction characteristics of magnesium alloy ZM-21

Friction plays a significant role in metal working, affecting the flow stress, the deformability, the surface finish, the tool life, etc. Magnesium alloy ZM-21 in the wrought condition is used generally in aerospace components, the present study being undertaken to assess the suitability of lubricants for the working of this alloy. The paper describes ring compression tests performed on the as-cast material with nine different lubricants in the temperature range 300–500°C, friction factors and flow stresses being determined for the different conditions. The ‘experimentally’ determined values of friction factor μ, obtained using the experimental calibration results of Male and Cockroft have been found to be related to the ‘theoretical’ friction factor (m, obtained using the theoretical calibration results of De Pierre et al.) through a second-order polynomial. A significant observation was a sharp change in friction factor at about 400°C. EPMA and differential scanning calorimetry (DSC) study of the material indicate the presence of a metastable phase in the as-cast condition which became dissolved during homogenisation at around 350°C, the rise in friction factor being attributable to this feature.