1Zn Magnesium Alloy Research Articles

Effect of indium and yttrium on the corrosion behavior of AZ63 magnesium alloy

Indium (In) and yttrium (Y) can activate and alleviate the corrosion of magnesium alloy, respectively. The effects of 1 wt% In and 1 wt% Y on the microstructure and electrochemical behaviors of Mg-6 wt%Al-3 wt%Zn (AZ63) magnesium alloy are investigated via materials characterizations associated with electrochemical techniques. The results showed that co-alloying of In and Y would increase the number of intermetallic phases in AZ63 by generating discrete Al2Y phase and continuous Mg17Al12 phase. During the process of corrosion, the corrosion of Mg-6 wt%Al-3 wt%Zn-1 wt%In-1 wt%Y(AZ63InY) initiates from the intermetallic phases and propagates locally. The corrosion products are apt to adhere on the corroded surface, underneath which a severe corrosion takes place due to the enhanced dissolution-reprecipitation effect of In on activating Mg.

Specimen Size Effect on Behavior of Mg–3Al–1Zn Magnesium Alloy in Macro to Micro-scale Deformation

Specimen Size Effect on Behavior of Mg–3Al–1Zn Magnesium Alloy in Macro to Micro-scale Deformation

Microstructure evolution and deformation mechanism of AZ80 alloy during die forging

Die forging is a processing method that can produce a size and shape close to the finished product and improve the mechanical properties of the alloy. In this paper, Mg–8Al-0.5Zn magnesium alloy was used to prepare stepped shaft by isothermal die forging. The microstructure and stress-strain state of different parts of stepped shaft forging were analyzed. The metal rheological law and microstructure evolution mechanism of AZ80 alloy during die forging were discussed. At the position of low stress and high strain state of the die forging, continuous dynamic recrystallization (CDRX) is the main deformation mechanism, and the microstructure is mainly composed of coarse un-dynamic recrystallized (unDRXed) grains and fine equiaxed dynamic recrystallized (DRXed) grains. The unDRXed grains have a strong basal texture, while the DRXed grains exhibit random orientations. At the position of high stress and low strain state of the die forging, {10–12} twinning is the main deformation mechanism, the parent grains show a strong basal texture, while {10–12} twins present [-12-10]-[01–10] double fiber texture parallel to forging direction (FD). The compressive strength and yield strength of the part in the low stress and high strain state are higher than those in the high stress and low strain state, but the fracture strain of the former is lower than that of the latter. The results of this study can provide a reference for the design of die forging die together with the blank shape and size, so as to meet the corresponding performance requirements of different parts of the die forging.

Influence of Sn and Zn on age-hardening behavior of Mg-6Al magnesium alloy

ABSTRACT In the present work, a thermally stable as-cast Mg-6wt% Al-3wt% Sn (AT63) and a commercial AZ series Mg-6wt% Al-3wt% Zn (AZ63) magnesium alloy were developed to study age-hardening behavior. Age-hardening behavior was compared at temperatures between 200°C and 350°C for a prolonged period. The former alloy AT63 has two precipitates, Mg17Al12 and Mg2Sn, showing a poor ageing profile, whereas the latter has only Mg17Al12 precipitate and significant age hardening. Scanning electron microscopy (SEM) was used to observe precipitate formation in the aged samples of both alloys under the same annealing conditions. It was concluded that adding Sn to Mg-6Al alloy slows down the formation of Mg17Al12 and consequently reduces the ageing effect, though it aids in forming a new precipitate Mg2Sn.

Mechanical Properties and Corrosion Behavior of Biodegradable Mg–0.5Zr–0.5Ca–xZn Magnesium Alloys

Mechanical properties and in vitro corrosion behavior of biodegradable Mg–0.5Zr–0.5Ca–xZn alloys in the simulated body fluid (SBF) solution are investigated. Zinc addition leads to a remarkable grain refinement in the as‐cast condition, as well as the formation of Ca2Mg6Zn3 and Mg7Zn3 compounds. As a result, the lean Mg–0.5Zr–0.5Ca–1Zn alloy shows the best combination of mechanical properties with an ultimate tensile strength (UTS) of 182 MPa, total elongation of 9.5%, and tensile toughness of 13 MJ m−3, which reveals ≈80%, 72%, and 190% improvements compared to those obtained for the Mg–0.5Zr–0.5Ca alloy, respectively. This sample also exhibits improved corrosion behavior, where a decrease in the corrosion current density (iCorr) is recorded via the addition of 1 wt% Zn. However, higher Zn additions result in the formation of a quasi‐continuous eutectic network with the consequent deterioration of tensile properties and increased effect of microgalvanic couples. The extreme grain refinement induced by the dynamic recrystallization (DRX) remarkably improves the overall mechanical properties of the hot extruded alloy but increased the iCorr. Accordingly, the properties of Mg–0.5Zr–0.5Ca alloys can be tailored for biomedical applications via Zn addition and thermomechanical processing.

Characterization of hot extrusion deformation behavior, texture evolution, and mechanical properties of Mg–5Li–3Sn–2Al–1Zn magnesium alloy

The effects of four different hot extrusion processes on the microstructure, texture, and mechanical properties of Mg–5Li–3Sn–2Al–1Zn alloys were investigated with the help of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) techniques. The results show that the magnesium alloy experienced dynamic recrystallization during the hot extrusion processes, the grain size was significantly refined compared with that of the cast alloy, and the mechanical properties of the alloy were significantly improved. After the 105° forward-parallel channel extrusion process, the alloy exhibited optimal strength and plasticity with 178 MPa, 270 MPa, and 21.03% for tensile yield strength, ultimate tensile strength, and elongation, respectively, which were 61.8%, 44.4%, and 134.4% higher compared to the homogeneous state. The increase in strength is attributed to fine grain strengthening, while the significant increase in plasticity is due to the weakening of the basal texture and the improved coordination of plastic deformation of the magnesium alloy following grain refinement.

Evolution and distribution of crystallographic texture on friction-stir welded joint of Mg-4.6Al-1.2Sn-0.7Zn magnesium alloy

The B-fiber texture in friction-stir welding of Mg–4.6Al–1.2Sn–0.7Zn magnesium alloy was investigated using electron-backscatter diffraction technique. The {0001} base plane of texture tended strongly to align with the effective geometric shear plane induced by the combined effect of the tool shoulder and the pin. The texture intensity is symmetrically distributed with respect to the weld centerline in shoulder-affected zone, while increases gradually from retreating side to advancing side in pin-affected zone. The inhomogeneous shear plastic strain and material transfer resulted in non-uniform distribution of texture on the welded joint.

Study of the Effect of Diamond Nanoparticles on the Structure and Mechanical Properties of the Medical Mg–Ca–Zn Magnesium Alloy

The paper addresses the production and investigation of the Mg–Ca–Zn alloy dispersion-hardened by diamond nanoparticles. Structural studies have shown that diamond nanoparticles have a modifying effect and make it possible to reduce the average grain size of the magnesium alloy. Reduction of the grain size and introduction of particles into the magnesium matrix increased the yield strength, tensile strength, and ductility of the magnesium alloy as compared to the original alloy after vibration and ultrasonic treatment. The magnesium alloy containing diamond nanoparticles showed the most uniform fracture due to a more uniform deformation of the alloy with particles, which simultaneously increased its strength and ductility.

Microstructure and Mechanical Properties of Friction Stir-Welded Dissimilar Joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn Alloys.

In order to clarify the microstructural evolution and the mechanical property of dissimilar friction stir-welded joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn magnesium alloys, two types of arrangement with ZK60 at advancing side (AS) or retreating side (RS) were adopted. The macrostructure and the microstructure of the dissimilar welded joints were discussed, and the microhardness and the transverse tensile properties of the joints were measured. There are three stirring sub-zones with different compositions and two clear interfaces within the joints. Due to the effect of both the original grain size of base materials and the growth of recrystallized grains, in the stir zone (SZ), the grain size of ZK60 increased slightly, while the grain size of Mg-4.6Al-1.2Sn-0.7Zn decreased significantly. The dissolution of precipitates was gradually significant from RS to AS within the SZ due to the gradual increase in strain and heat. The grain refinement led to an increase in hardness, while the dissolution of precipitates resulted in a decrease in hardness. The performance of the joints obtained with ZK60 placed on the RS is slightly better than that of that on the AS. The tensile fracture of both joints occurred at the interface between SZ and the thermos-mechanical affected zone at the AS, and showed a quasi-dissociative fracture.

Tensile twin evolution of Mg–3Al–1Zn magnesium alloy during high-strain rate deformation

In order to investigate the evolution of tensile twin in Mg–3Al–1Zn (AZ31) magnesium alloy under high-strain rate impaction, the cylindrical specimens were compressed along the rolling direction under the strain rate of 1600 s−1 by use of split Hopkinson pressure bars equipped with stop rings with different thicknesses. The microstructure was observed by electron back-scatter diffraction. The results show that tensile twinning dominates the early plastic deformation and the area fraction of tensile twins is increased with the increase of deformation strain. Furthermore, when the deformation strain is beyond ∼10%, plastic deformation is mainly dominated by dislocation slips. In addition, most of tensile twins activated in a single grain belong to a variant or a variant pair, which has the highest Schmid factor among all the variants.

The Formation of 14H-LPSO in Mg-9Gd-2Y-2Zn-0.5Zr Alloy during Heat Treatment.

There is a new long-period stacking ordered structure in Mg–RE–Zn magnesium alloys, namely the LPSO phase, which can effectively improve the yield strength, elongation, and corrosion resistance of Mg alloys. According to different types of Mg–RE–Zn alloy systems, two transformation modes are involved in the heat treatment transformation process. The first is the alloy without LPSO phase in the as-cast alloy, and the MgxRE phase changes to 14H-LPSO phase. The second is the alloy containing LPSO phase in the as-cast state, and the 14H-LPSO phase is obtained by the transformations of 6H, 18R, and 24R. The effects of different solution parameters on the second phase of Mg–9Gd–2Y–2Zn–0.5Zr alloy were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The precipitation mechanism of 14H-LPSO phase during solution treatment was further clarified. At a solution time of 13 h, the grain size increased rapidly initially and then decreased slightly with increasing solution temperature. The analysis of the volume fraction of the second phase and lattice constant showed that Gd and Y elements in the alloy precipitated from the matrix and formed 14H-LPSO phase after solution treatment at 490 °C for 13 h. At this time, the hardness of the alloy reached the maximum of 74.6 HV. After solution treatment at 500 °C for 13 h, the solid solution degree of the alloy increases, and the grain size and hardness of the alloy remain basically unchanged.

Tube equal channel angular extrusion (tECAE) of Mg–3Al–1Zn alloy

This study describes a severe plastic deformation processing technique for tubular materials, in the interest of enhancing mechanical properties via grain refinement and crystallographic texture control. The process, dubbed as tube equal channel angular extrusion (tECAE), is used to process the Mg–3Al–1Zn (AZ31) magnesium alloy at low temperatures. Mg alloys often suffer from low strength levels derived from coarse grain size, strong crystallographic texture, and mechanical anisotropy; hence, AZ31 acts as an ideal candidate for tECAE, as AZ31 and other Mg alloys tubes have excellent potential application in various industries. Here, the texture evolution of one pass of tECAE processing at 200 °C, 175 °C, and 120 °C was assessed, where tECAE produced drastically refined grains and increased strength levels after only one pass. The texture evolution and the active deformation modes, and their relative activities, were successfully predicted using a viscoplastic self-consistent (VPSC) crystal plasticity model as a function of processing temperature, for the first time for the tECAE process. Overall, tECAE is shown to be a useful technique for quickly obtaining improved mechanical properties in Mg alloy tubes, and it can be applied to other materials in tubular form as well. • Tube ECAE processing successfully produced fine grained Mg-3Al-1Zn tubes. • Tube ECAE SPD processed AZ31 directly at 120 °C. • Improvement in mechanical properties and texture modification are obtained via tECAE. • VPSC modeling predicted texture and deformation mode activities.

The Effect of Pulsed Nanosecond Laser Irradiation on the Corrosion Resistance of Mg–Al–Zn Magnesium Alloy

The corrosion resistance of Mg–Al–Zn magnesium alloy with coarse-grained and ultrafine-grained structures before and after the treatment of the surface of the alloy with pulsed nanosecond laser irradiation is studied. It is found that this treatment significantly increases the resistance of the alloy to its dissolution in a 0.9% NaCl saline only under the condition of preliminary formation of a uniform ultrafine-grained structure in the bulk of the sample. The observed effect can be considered as a promising method for the treatment of the surface of medical devices made of biodegradable magnesium alloys.

Microstructure and Mechanical Properties of Mg–3Al–Zn Magnesium Alloy Sheet by Hot Shear Spinning

Hot shear spinning experiments with Mg–3.0Al–1.0Zn–0.5Mn (AZ31B, wt%) magnesium alloy sheets were conducted at various temperatures, spindle speeds and feed ratios to investigate the effects of these processing parameters on the microstructure, crystallographic texture and mechanical properties. The AZ31B sheet displayed good shear formability at temperatures from 473 to 673 K, spindle speeds from 300 to 600 rev/min and feed ratios from 0.1 to 0.5 mm/rev. During the dynamic recrystallization process, the grain size and texture were affected by the deformation temperature of the hot shear spinning process. Each of the spun sheets presented a strong basal texture, and the c-axis of most of the grains was parallel to the normal direction. The optimal hot shear spinning parameters were determined to be a temperature of 473 K, a spindle speed of 300 rev/min and a feed ratio of 0.1 mm/rev. The yield strength, ultimate tensile strength and elongation in the rolled direction reached 221 MPa, 288 MPa and 14.1%, and those in the transverse direction reached 205 MPa, 280 MPa and 12.4%, respectively. The improved strength and decreased mechanical anisotropy resulted from the fine grain size and strong basal texture.

Tailoring the mechanical properties of Mg–Zn magnesium alloy by calcium addition and hot extrusion process

Grain refinement and enhanced mechanical properties of Mg–2Zn-xCa alloys (with a wide range of calcium contents from 0 to 5 wt%) were studied in both as-cast and extruded conditions. It was revealed that Ca addition can effectively refine the grain size of the ingots based on the growth restriction factor (GRF) mechanism, where at high Ca additions, the dendritic microstructure was obtained. By increasing the amount of Ca, the binary Mg–Zn phase was replaced by the Ca2Mg6Zn3 phase and at high Ca contents, the Mg2Ca phase appeared in the microstructure. The tensile properties were enhanced at low Ca additions (up to 0.3 wt%) due to the grain refinement but they were deteriorated at higher Ca additions due to the formation of grain boundary second phases. Accordingly, the ultimate tensile strength (UTS) of 228 MPa and total elongation of 20% was obtained for the as-cast Mg–2Zn-0.3Ca (ZX20) alloy. During hot extrusion, significant grain refinement and the fracturing and dispersion of second phase particles were observed. The grain size refinement beyond ~1 wt% Ca was negligible and extrusion defects were observed at higher Ca contents, and hence, the best combination of mechanical properties was obtained for the Mg–2Zn–1Ca (ZX21) alloy with UTS of 283 MPa and elongation to failure of 29%. This alloy showed a desirable work-hardening behavior and the best combination of tensile properties, where the product of tensile strength and total elongation reached as high as ~8000 MPa%. Finally, the yield stress of the alloys was correlated to the average grain size via the classical Hall-Petch plot with a slope of 228.5 MPa μm0.5.

Characterization of the corrosion performances of as‐cast Mg–Al and Mg–Zn magnesium alloys with microarc oxidation coatings

AbstractIn the present study, corrosion‐protective microarc oxidation (MAO) coatings were prepared on AZ31B, AZ80, and ZK60 cast magnesium alloy substrates in an alkaline silicate electrolyte. The corrosion performances of the uncoated and MAO‐coated alloys were investigated using electrochemical and salt spray chamber corrosion tests. The microstructure characterization and experimental results show that among the three alloys studied, the ZK60 Mg alloy exhibited the best and AZ31B the least corrosion resistance under the salt spray conditions. The MAO coating provided robust corrosion protection of the Mg substrates and resulted in a significant decrease in the corrosion rate of the alloys by 3–4 orders of magnitude. The MAO coating on ZK60 alloy showed better corrosion protectiveness than that on the AZ series alloys due to the incorporation of different alloying elements in the coating, especially the Zn and Al elements, which are from the Mg substrate. The corrosion performances and mechanisms of the uncoated and MAO‐coated Mg alloys are interpreted in terms of the microstructure and phase/chemical compositions of both the substrates and coatings.

Improved Mg–Al–Zn Magnesium Alloys Produced by High Energy Milling and Hot Sintering

Powders of commercially pure magnesium (c.p. Mg), AZ91 magnesium alloy and zinc were milled using a high-energy mill. The effect of high energy milling (HEM) on powders morphology, chemical composition, crystallite size and compaction of different powders mixtures were studied. After compaction, samples were thermally treated at 450 °C and both density and hardness were evaluated. It was found that as milling speed and time increases, the AZ91 alloy and c.p. Mg particles were deformed and fractured up to sizes below 10 μm. X-ray diffraction patterns for both the c.p. Mg and the AZ91 powders revealed that the milling process induced changes in both the α-Mg and the β-Mg17Al12 phases. By increasing the milling speed, the crystallite size decreases by up to 70% for AZ91 powders and by 80% for magnesium powders. The relative densities of the compacted AZ samples were greater than 85% and this parameter increased for all samples after thermal treatment at 450 °C, obtaining densities higher than 88%. Hardness measurements disclosed values as high as 84.3 HR15T. Theoretical calculations of mechanical strength were obtained for all samples based on the hardness values measured, finding very encouraging results for the three Mg alloys.

Analysis of {10–12} twinning variants’ selection behavior during multi-directional compression in Mg–3Al–1Zn magnesium alloy

The {10–12} twinning activities of Mg–3Al–1Zn magnesium alloy during multi-directional compression were investigated by in situ EBSD technology. The specimen was pre-compressed to a strain of 3.2% along TD, followed by a compression with a strain of 2.6% along RD, and finally a compression with a strain of 2.5% along TD. The Schmid factor, strain compatibility factor (m′) and twinning strain tensor (e) were calculated to analyze the twinning variant selection. The results show that four types of twinning behaviors can be observed during multi-directional compression: (1) the growth of twin lamellas generated from previous compression; (2) the nucleation of new {10–12} twins in existing twins; (3) the nucleation of new {10–12} twins in initial grains; and (4) detwinning. Some grains show only one twinning behavior within a grain, while some grains exhibit two or more twinning behaviors within a single grain. The variant selection of {10–12} twins for twin pairs and twin chains in neighboring grains is dominated by high Schmid factor and high strain compatibility factor. Because of good accommodation between neighboring grains, the simultaneous detwinning and retwinning behaviors developed in twin pairs or twin chains during multi-directional compression.

Characterization of the High-Strength Mg–3Nd–0.5Zn Alloy Prepared by Thermomechanical Processing

Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medical applications. Superior mechanical properties of these materials can be achieved by thermomechanical processing such as extrusion or rolling and by aging treatment, which can significantly strengthen the alloy. The question remains especially about the connection of texture strength created in the alloys based on the specific conditions of preparation. This work focuses on the Mg–3Nd–0.5Zn magnesium alloy prepared by hot extrusion of the as-cast state at two different temperatures combined with heat pre-treatment. Extrusion ratio of 16 and rate of 0.2 mm/s at 350 and 400 °C were selected for material preparation. The structures of prepared materials were studied by scanning electron microscopy and transmission electron microscopy. The effect of microstructure on mechanical properties was evaluated. Obtained results revealed the strong effect of thermal pre-treatment on final microstructure and mechanical properties of extruded materials. The Hall–Petch relation between grain size and tensile yield strength has been suggested in this paper based on the literature review and presented data. The observed behavior strongly supports the fact that the Hall–Petch of extruded Mg–3Nd–0.5Zn alloys with different texture intensities cannot be clearly estimated and predicted. In addition, Hall–Petch relations presented in literature can be sufficiently obtained only for fraction of the Mg–3Nd–0.5Zn alloys.

Effect of Rotary Forging on Microstructure and Mechanical Properties of Mg–3Al–1Zn Magnesium Alloy

Effect of Rotary Forging on Microstructure and Mechanical Properties of Mg–3Al–1Zn Magnesium Alloy