DRXed Regions Research Articles

Achieving enhanced mechanical properties of extruded Mg-Gd-Y-Zn-Zr alloy by regulating the initial LPSO phases

In this paper, “bimodal microstructure” and enhanced mechanical properties of extruded Mg-Gd-Y-Zn-Zr alloy is achieved by regulating the initial long-periodic stacking-ordered (LPSO) phases, the effect of blocky LPSO phase and lamellar LPSO phase on the dynamic recrystallization (DRX) behavior and the formation mechanism of bimodal microstructure are systematically investigated, the deformation modes, strengthening and toughening mechanism and fracture behavior of the “bimodal microstructure” are analyzed by slip traces. Blocky LPSO phase has significant particle stimulated nucleation (PSN) effect to promote DRX. The effect of lamellar LPSO phase on DRX depends on the size, fragmented lamellar LPSO with small size promotes numerous DRXed grains through the PSN effect, while continuous intragranular lamellar LPSO with large size inhibits DRX by hindering slip and grain boundary rotation, which is the key factor to form the bimodal microstructure. The almost fully DRXed H-510 sample has the lowest strength, and the H-525 sample with “bimodal microstructure” achieves enhanced comprehensive mechanical properties (ultimate tensile strength, yield strength and elongation of 383 MPa, 308 MPa and 9.2 %, respectively), which is related to the significant texture strengthening and dislocation strengthening of large-sized unDRXed grains, as well as strain coordination of higher DRXed grains fraction. The deformation mode of the DRXed regions is grain boundary sliding, while the unDRXed regions are dominated by prismatic slip, the strain incompatibility between the two is the decisive factor causing microcracks propagation and final fracture. This paper will provide theoretical guidance for the initial microstructure design of strength-plasticity synergistic Mg-Gd-Y-Zn-Zr alloys with bimodal microstructure.

300 MPa grade high-strength ductile biodegradable Zn-2Cu-xMg (x = 0.08, 0.15, 0.5, 1) alloys: The role of Mg in bimodal grain formation

300 MPa grade biodegradable Zn-2Cu-xMg (0.08, 0.15, 0.5, and 1 wt.%) alloys with different bimodal grain structures were obtained by casting and hot extrusion. The effects of the Mg element on the microstructure, mechanical properties, and dynamic recrystallization (DRX) behavior of the as-extruded Zn-2Cu-xMg alloys were investigated. The obtained results showed that CuZn4 butterfly particles and eutectic net structure (η-Zn + Mg2Zn11) are formed in the as-cast Zn-2Cu-xMg alloys. The as-extruded Zn-2Cu-0.08Mg and Zn-2Cu-0.15Mg alloys exhibited finer DRXed and coarser unDRXed grains with an average grain size of 8.5–8.8 μm, while Zn-2Cu-0.5Mg and Zn-2Cu-1Mg alloys were almost composed of completed DRXed grains with an average grain size of 4.2–6.5 μm. Nanoprecipitates ε-CuZn4 were uniformly precipitated in both DRXed regions and unDRXed regions. Continuous DRX (CDRX) and twinning-induced DRX (TDRX) were the main mechanisms at a low Mg content; Discontinuous DRX (DDRX) and particle-stimulated nucleation (PSN) were strengthened with the addition of Mg. The improved yield strengths in Zn-2Cu-xMg originate from grain boundary strengthening, Orowan strengthening, and hetero-deformation-induced (HDI) strengthening. The fracture elongations are mainly affected by the synergistic effect of bimodal grains, non-basal < c + a > dislocations, and the secondary phases.

High Performance Mg Alloy with Designed Microstructure and Phases.

A high strength and ductile Mg-Gd-Y-Zn-Zr alloy was designed and fabricated. The local strain evolution of the alloys during plastic deformation was analyzed using high-resolution digital image correlation (DIC). The results showed that the β particles, nano-sized γ' phases, and LPSO phases were distributed in the as-extruded alloy and a bimodal microstructure was exhibited, including elongated un-dynamic recrystallized grains and fine dynamic recrystallized grains. With increasing extrusion ratio, the grain size remained, with the volume fraction of dynamic recrystallization of the as-extruded alloy increasing from 30% to 75%, and the as-extruded alloy exhibited a high strength-ductility synergy, which is attributed to the grain refinement, extensive β particles, and elongated block-shaped LPSO phases. The strain evolution analysis showed that a strain-transfer from un-DRXed regions to adjacent DRXed regions and LPSO phases can promote uniform plastic deformation, which tends to improve the ductility of the alloy.

Role of Ca content on microstructure, mechanical properties and strain evolution of as-rolled Mg-Al-Ca-Zn-Mn alloy

The role of Ca content (0.5, 1.0, 2.0 wt.%) on microstructure, mechanical properties and strain evolution of as-rolled Mg-Al-Ca-Zn-Mn alloy was thoroughly investigated in this work. The results indicate that the primary second phase transformed from the Mg17Al12 phase to the Al2Ca phase after homogenization, and the amount of Al2Ca phase increased significantly with increasing Ca content. After hot rolling, the alloys exhibited the typical bimodal microstructure composed of fine dynamic recrystallized (DRXed) grains and coarse elongated un-DRXed grains, the area fraction of the DRXed regions increased with increasing Ca content. Besides, a large number of submicron-sized as well as nano-scaled spherical Mg17Al12 phases dynamically precipitated along the DRXed grain boundaries in all alloys, which promoted the DRX and restricted the grain growth. During rolling deformation, DRX preferentially occurred near the primary second phases and shear bands by the particle stimulated nucleation (PSN) and shear band induced nucleation (SBIN) mechanism in the alloys. The ultimate tensile strength (UTS), yield strength (YS), and elongation to failure (EF) along the rolling direction (RD) of the Mg-8.0Al-1.0Ca-1.0Zn-0.4Mn (wt.%) sheet were 393 MPa, 334 MPa and 8.7 %, respectively. Such high strength was mainly attributed to fine DRXed grains, high number density of dynamically precipitated Mg17Al12 phases and strongly textured un-DRXed grains with numerous sub-structures. The reasonable DRX ratio moderated strain localization and thus stabilized tensile deformation, leading to moderate plasticity of the alloy.

Influence of bimodal microstructure on strength and ductility of as-extruded Mg-Gd-Y-Zr alloy

This paper studied the role of layered bimodal structure in the strength-ductility balance of Mg-8Gd-4Y-0.4Zr (wt%) alloys under as-extruded conditions. The various bimodal microstructure, consisting of fine dynamically recrystallized grains and elongated un-dynamically recrystallized grains along extrusion direction, were controlled by different extrusion ratios. The mechanical properties were then discussed in detail. The local strain evolution was investigated in the alloys based on in situ testing and analyzed with electron backscattered diffraction and digital image correlation. The fracture behavior of the alloys was characterized by 3-Dimensional X-Ray Microscopy. The alloys with an extrusion ratio of 7.5 exhibited high tensile yield strength of 338 MPa and ductility of 13.2%, resulting from grain boundary strengthening of fine DRXed grains, and dislocation strengthening of elongated un-DRXed grains and Mg5RE particles. The strain evolution analysis showed that the slips and rotations of DRXed grains contributed to relieving strain localization at the interface. Additionally, the layered structure assisted local strain dispersion and uniformed strain distribution, improving the strength and ductility of alloys. The microcracks primarily nucleated and propagated at the un-DRXed regions. The DRXed regions can refine microcracks and enhance deformation compatibility.

Deformation modes and fracture behaviors of peak-aged Mg-Gd-Y alloys with different grain structures

The ductility and toughness of peak-aged (PA) Mg-RE alloys are significantly influenced by their grain structure characteristics. To investigate this issue, we examined PA Mg-8.24Gd-2.68Y (wt.%) alloys with two distinct grain structures: an extruded-PA sample with dynamic recrystallized (DRXed) fine grains and coarse hot-worked grains, and an extrusion-solution treated and PA sample with grown large equiaxed grains. The results showed that the extruded-PA sample demonstrated a favorable combination of tensile strength (426 MPa) and ductility (7.0 %). Although intergranular microcracks nucleated in the DRXed region due to strain incompatibility, crack propagation was impeded by the DRXed fine grains, inducing intrinsic and extrinsic toughening mechanisms. On the other hand, the hot-worked grains in the extruded-PA sample initiated transgranular cracks after a relatively high strain, attributed to the strain partitioning effect, ultimately leading to failure. In comparison, the solution-treated-PA sample exhibited lower tensile strength and ductility (338 MPa and 3.7 %, respectively). Intergranular cracks nucleated in the CG sample before necking, and the readily formed critical crack, facilitated by the large grain size, exhibited unstable crack growth, resulting in premature failure. This work offers valuable insights for designing high-performance PA Mg-RE alloys and preventing premature failure in practical applications.

Optimizing LPSO phase to achieve superior heat resistance of Mg–Gd–Y–Zn–Zr alloys by regulating the Gd/Y ratios

The microstructural features of long period stacking ordered (LPSO) phase in Mg–(11-x)Gd–xY–1Zn–0.3Zr (wt.%) alloys were optimized by adjusting Gd/Y ratios to10:1, 8:3, 6:5, 4:7 and 2:9, respectively. Superior high-temperature strength was successfully obtained in the extruded 6Gd–5Y alloy with ultimate tensile strength (UTS) values of 338 MPa and 286 MPa at 250 °C and 300 °C, respectively. In the as-cast alloys, with the decrease of Gd/Y ratio, the type of intermetallic compound gradually changed from (Mg, Zn)3(Gd, Y) (W) to LPSO phase. After homogenization, the W phase was completely converted to LPSO phase except for the 10Gd–1Y alloy. Importantly, the block-shaped LPSO phases with the smallest size and the abundant lamellar LPSO phases were formed in the 6Gd–5Y alloy, which significantly influenced the microstructures of the extruded alloy. Firstly, the small sized block-shaped LPSO phase before extrusion provided favorable conditions for the formation of thin plate-shaped LPSO phase at DRXed regions, which effectively hindered the grain boundary migration at high temperature due to superior thermal stability. Secondly, the profuse lamellar LPSO phases prior to extrusion contributed to the highest density of low angle grain boundaries (LAGBs) and residual dislocations in the extruded 6Gd–5Y alloy, which obstructed dislocation slip at elevated temperatures. In addition, the abundant lamellar LPSO phase also caused the fine DRXed grain size and strong basal texture to enhance the high-temperature strength of the extruded 6Gd–5Y alloy.

Achieving high strength-ductility synergy in a Mg97Y1Zn1Ho1 alloy via a nano-spaced long-period stacking-ordered phase

Achieving high strength in Mg alloys is usually accompanied by ductility loss. Here, a novel Mg 97 Y 1 Zn 1 Ho 1 at. % alloy with a yield strength of 403 MPa and an elongation of 10% is developed. The strength-ductility synergy is obtained by a comprehensive strategy, including a lamella bimodal microstructure design and the introduction of nano-spaced solute-segregated 14H long-period stacking-ordered phase (14H LPSO phase) through rare-earth Ho alloying. The lamella bimodal microstructure consists of elongated un-recrystallized (un-DRXed) coarse grains and fine dynamically-recrystallized grains (DRXed regions). The nano-spaced solute-segregated 14H LPSO phase is distributed in DRXed regions. The outstanding yield strength is mainly contributed by grain-boundary strengthening, 18R LPSO strengthening, and fiber-like reinforcement strengthening from the nano-spaced 14H LPSO phase. The high elongation is due primarily to the combined effects of the bimodal and lamellar microstructures through enhancing the work-hardening capability.

Microstructure evolution and mechanical properties of high-strength Mg-Gd-Y-Zn-Mn alloy processed by asymmetric hot rolling

Asymmetric hot rolling was used to fabricate the high-strength Mg-9Gd-4Y–1Zn-0.8Mn (wt.%) alloys, which is strengthened by the lamellar long-period stacking ordered (LPSO) phases inside grains and the block-shaped LPSO phases surrounding grain boundaries. The reduction in total thickness shows a significant impact on the microstructure, texture, and mechanical properties of the alloy sheets. By keeping the velocity ratio between the top and lower rollers at 1.3, the shear strain is introduced all across the sheet thickness. The as-rolled sample exhibits a bimodal-grained structure made up of fine recrystallized (DRXed) grains with relatively random orientation and coarse elongated non-recrystallized (unDRXed) grains with intense basal texture and profuse substructure. As rolling strain increases, the volume fraction of the DRXed region and the basal texture intensity of the unDRXed region gradually increase. The dominating prismatic <a> slip as well as the moderate basal <a> slip and pyramidal <c+a> slip are activated during rolling. The triggering of prismatic <a> slip, among the activated multiple slip systems, results in the development of [101¯0]//RD texture component at high strains. The alloy sheet that underwent severer rolling strain (56.3%R sample) shows higher ultimate tensile strength (411 MPa) and tensile yield strength (348 MPa) but lower elongation to failure (3.5%). The dominant strengthening mechanisms for the preferable mechanical properties should be grain boundary strengthening of fine DRXed grains, texture strengthening of coarse elongated unDRXed grains, short-fiber strengthening of block-shaped LPSO phases, and dispersion strengthening of profuse lamellar LPSO phases and dense tiny Mg5(Gd, Y) particles.

Compressive properties of a severely deformed fine-grained Mg−6Gd−3Y alloy

An extruded Mg−6Gd−3Y alloy was processed by 6 passes of simple shear extrusion (SSE) at 553 K to refine the microstructure. The microstructural studies were performed through electron back-scattered diffraction (EBSD) and also transmission electron microscopy (TEM) to investigate the microstructural features which emerged after SSE. It was revealed the SSE-processed alloy had a duplex microstructure containing both fine dynamically recrystallized (DRX) grains and some large deformed grains. A relatively high fraction of low angle grain boundaries (LAGBs), induced within the un-DRXed deformed grains, was identified by EBSD results. TEM studies revealed the formation of round Mg5Gd-type nano-particles through dynamic precipitation only in the DRXed regions of microstructure in the SSE-processed alloy. Compressive mechanical properties and strain hardening behavior of the alloys were assessed by compression testing of both alloys at room temperature. SSE processing resulted in enhanced yield stress and reduced ductility. Both the extruded and SSE-processed alloys exhibited a three-stage strain hardening behavior with a much more pronounced stage II of hardening in the latter one. According to the mechanical properties results, there was a noticeable difference in the strain hardening rate and also dislocation storage rate of the extruded and SSE-processed alloys. This discernible strain hardening behavior of the two alloys was attributed to the formation of fine DRXed grains, dynamic precipitation of nano-sized Mg5Gd particles, and induction of LAGBs, which emerged after SSE.

Investigation on the microstructure, texture and mechanical properties of Mg-Gd-Y(-Zn)-Zr alloys under indirect extrusion

This work mainly studies the microstructure, texture and mechanical properties of Mg-8.5Gd-2.5Y-0.3Zr (wt%) (0Zn) and Mg-8.5Gd-2.5Y-0.5Zn-0.3Zr (wt%) (0.5Zn) alloys under indirect extrusion at different temperatures. Dynamic recrystallization in the two alloys occurs via discontinuous dynamic recrystallization (DDRX) as well as continuous dynamic recrystallization (CDRX) mechanisms under extrusion at both 450 °C and 500 °C. Dynamic precipitation of β-Mg5RE phases takes place along with the DRX process in both alloys when extruded at 450 °C, while it is absent at 500 °C. The addition of 0.5 wt% Zn promotes the dynamic precipitation, leading to a well distribution of β phases in all the DRXed regions of 0.5Zn alloy, compared to a local distribution only in partial DRXed regions of 0Zn alloy. The well distributed β phases and the existence of γ’ phase caused by adding trace Zn result in finer DRXed grains and lower recrystallization fraction in the 0.5Zn alloy than that in the 0Zn alloy. The as-extruded 0Zn and 0.5Zn alloys exhibit quite weak texture in the DRXed regions. In particular, a prismatic texture component with basal plane perpendicular to the extrusion direction is formed, which is slightly strengthened by the addition of Zn and the promotion of extrusion temperature. The experimental results suggest the formation of this texture is primarily correlated with the growth advantage of relevant grains. The addition of trace Zn can obviously enhance the strength and stimulate the occurrence of yield point under tension, which is weakened with increasing the extrusion temperature. The present results demonstrate the important role of Zn addition and extrusion temperature on the microstructure, texture and mechanical properties of Mg-Gd-Y alloys.

Bimodal grain structure formation and strengthening mechanisms in Mg-Mn-Al-Ca extrusion alloys

The effects of small additions of calcium (0.1% and 0.5%11All compositions in weight percentage.) on the dynamic recrystallization behavior and mechanical properties of as-extruded Mg-1Mn-0.5Al alloys were investigated. Calcium microalloying led to the formation of Al2Ca in as-cast Mg-1Mn-0.5Al-0.1Ca alloy and both Mg2Ca and Al2Ca phases in Mg-1Mn-0.5Al-0.5Ca alloy. The formed Al2Ca particles were fractured during extrusion process and distributed at grain boundary along extrusion direction (ED). The Mg2Ca phase was dynamically precipitated during extrusion process, hindering dislocation movement and reducing dislocation accumulation in low angle grain boundaries (LAGBs) and hindering the transformation of high density of LAGBs into high angle grain boundaries (HAGBs). Therefore, a bimodal structure composed of fine dynamically recrystallized (DRXed) grains and coarse unDRXed regions was formed in Ca-microalloyed Mg-1Mn-0.5Al alloys. The bimodal structure resulted in effective hetero-deformation-induced (HDI) strengthening. Additionally, the fine grains in DRXed regions and the coarse grains in unDRXed regions and the dynamically precipitated Mg2Ca phase significantly enhanced the tensile yield strength from 224 MPa in Mg-1Mn-0.5Al to 335 MPa and 352 MPa in Mg-1Mn-0.5Al-0.1Ca and Mg-1Mn-0.5Al-0.5Ca, respectively. Finally, a yield point phenomenon was observed in as-extruded Mg-1Mn-0.5Al-xCa alloys, more profound with 0.5% Ca addition, which was due to the formation of (101¯2)extension twins in unDRXed regions.

A new strong and ductile multicomponent rare-earth free Mg–Bi-based alloy achieved by extrusion and subsequent short-term annealing

A new multicomponent rare-earth free low-alloyed Mg-1.0Bi-1.0Mn-1.0Al-0.5Ca-0.3Zn (wt.%) alloy is prepared by low-temperature and low-speed extrusion. The as-extruded sample has an ultra-high yield strength (∼425 MPa) but low elongation-to-failure (∼2.1%) mainly due to a bimodal grain structure containing ultra-fine recrystallized (DRXed) grains and large-sized unDRXed regions with a strong basal fiber texture feature, accompanied by a certain amount of micro-scale second phases (Al8Mn5 and Mg2Bi2Ca) and the uniformly distributed nano-scale α-Mn particles. More importantly, the excellent strength-ductility synergy is realized in the annealed samples after appropriate short-term annealing, and the yield strength and elongation-to-failure can reach ∼378 MPa and ∼16.8%, respectively. The effective inhibition of grain growth by grain boundary co-segregation of solutes and pinning effect of α-Mn nanoparticles is crucial for the annealed samples to maintain the relatively high strength. The formation of a new heterogeneous fibrous structure containing fine/coarse DRXed grains and thin fibrous unDRXed regions, along with weak basal fiber texture and low-density residual dislocations, is a key factor for the annealed sample to significantly enhance the ductility. Hence, such a new high strong and ductile low-alloyed Mg–Bi-based alloy will be helpful for enriching high performance low-cost wrought Mg alloy series to achieve extensive applications in industries.

Biodegradable Zn-Cu-Mn alloy with suitable mechanical performance and in vitro degradation behavior as a promising candidate for vascular stents

Recently, zinc (Zn) alloy has been considered as a promising biodegradable material due to its excellent physiological degradable behavior and acceptable biocompatibility. However, poor mechanical performance limits its application as vascular stents. In this study, novel biodegradable Zn-2.2Cu-xMn (x = 0.4, 0.7, and 1.0 wt%) alloys with suitable mechanical performance were investigated. The effects of Mn addition on microstructure, mechanical properties, and in vitro degradation of Zn-2.2Cu-xMn alloys were systematically investigated. After adding Mn, dynamic recrystallization (DRX) during hot extrusion was promoted, resulting in slightly finer grain size, higher DRXed regions ratio, and weaker texture. And volume fraction and number density of second phase precipitates (micron, submicron, and nano-sized ε and MnZn13 phase) and the concentration of (Cu, Mn) in the matrix were increased. Therefore, Zn-2.2Cu-xMn alloys exhibited suitable mechanical performances (strength >310 MPa, elongation >30%) mainly due to the combination effects of grain refinement, solid solution strengthening, second phase precipitation hardening, and texture weakening. Moreover, the alloys maintained good stability of mechanical properties within 18 months and good elongation over 15% even at a high strain rate of 0.1 s−1. In addition, the alloys presented appropriate in vitro degradation rates in a basically uniform degradation mode and acceptable in vitro cytocompatibility. The above results indicated that the newly designed biodegradable Zn-2.2Cu-0.4Mn alloy with suitable comprehensive mechanical properties, appropriate degradation behavior, and acceptable cytocompatibility is a promising candidate for vascular stents.

Achieving high strength-ductility in a wrought Mg–9Gd–3Y–0.5Zr alloy by modifying with minor La addition

Effects of 0.5 wt% La addition on microstructures and mechanical properties of a traditional hot-extruded Mg–9Gd–3Y–0.5Zr alloy were thoroughly investigated in this work. The results indicate that minor La addition obviously improves the alloy’s mechanical performance at room temperature, accomplished an ultra-high tensile yield strength of 480 MPa with the elongation of ~6%, although leading to much lower high-temperature strength. Microstructural analysis reveals that after extrusion, minor La addition leads to a significantly higher level of recrystallization (the volume fraction is improved from 21% to 68%), much finer dynamically recrystallized (DRXed) grains (the average sizes are refined from 4.12 µm to 3.26 µm), and also finer non-recrystallization stripes. La addition promoting recrystallization is mainly attributed to the finer grains and much more intermetallics not only at grain boundaries but also in α-Mg grains of the ingots before extrusion. During peak-aging, minor La addition does not change intermetallics/precipitates in both DRXed grains and non-recrystallized regions except some extra coarse Mg17La2 particles mainly in extrusion stringers. Therefore, minor La addition improving both strength and ductility of the hot-extruded Mg–9Gd–3Y–0.5Zr alloy at room temperature is mainly by grain-refinement strengthening which is also the underlying cause for the lower work hardening coefficient, high-temperature strength but higher ductility.

Microstructures and mechanical properties of a Mg–9Gd−3Y−0.6Zn−0.4Zr (wt.%) alloy modified by Y-rich misch metal

Microstructural evolutions and mechanical properties of a Y-rich misch metal modified Mg–9Gd−3Y−0.6Zn−0.4Zr (wt.%) alloy were investigated. In the as-cast sample, the intermetallic phases are Mg5RE, Mg3RE and 14H-type long-period stacking ordered (LPSO) phase. After solution, all Mg3RE and most Mg5RE were dissolved while the 14H-LPSO plates were coarsened. The as-extruded alloy has a bimodal structure of ultra-fine dynamically recrystallized (DRXed) grains and coarse un-recrystallized grains, and is with a typical non-fiber texture. Disintegrated Mg5RE and 14H-LPSO particles aggregate in extrusion stringers while fine dynamically precipitated Mg5RE particles distribute at grain boundaries. After peak-aging, ultra-thin basal γ’’ and prismatic β’ precipitated in DRXed grain and un-recrystallized regions, respectively. The yield strength of the as-extruded and peak-aged alloys reaches to 385 MPa and 481 MPa, respectively, at room temperature, and to 320 MPa and 350 MPa, respectively, at 250 °C. Grain boundary strengthening from both grain boundaries and sub-grain boundaries in DRXed and un-recrystallized regions, respectively, and precipitation strengthening were revealed as the dominant strengthening mechanisms.

Effects of Ce Addition on Mechanical and Corrosion Properties of the As-Extruded Mg-Zn-Ca Alloy

The microstructure and corrosion properties of the as-extruded Mg-Zn-Ca alloy with and without Ce addition are investigated. The microstructure was characterized by optical microscopy, scanning electron microscopy coupled with electron backscatter diffraction detector. Ce addition retarded dynamic recrystallization during deformation, which resulted in the formation of bimodal microstructure with finely dynamically recrystallized (DRXed) grains and coarsely unDRXed grains. Texture of the DRXed region was weakened after small addition of Ce, mainly attributing to particle stimulated nucleation. The strength enhancement for the Ce containing Mg-Zn-Ca alloy was attributed to the fine microstructure and strong texture. Corrosion results indicated that Ce addition deteriorated corrosion resistance in 3.5 wt.% NaCl solution of the as-extruded Mg-Zn-Ca alloy, which was related to the dispersed second phases, refined microstructure and weak basal texture in DRXed region.

Effects of deformation parameters on microstructure and texture of Mg–Zn–Ce alloy

Abstract Compression tests were performed on the Mg–6Zn–0.5Ce (wt.%) alloy using a Gleeble–1500 thermo- mechanical simulator testing system at temperatures of 250, 300, 350 °C and strain rates of 0.001, 0.01, 0.1 s−1. The microstructure and texture evolution of the Mg–6Zn–0.5Ce alloy during hot compression were investigated by optical microscopy (OM) and electron backscattered diffraction (EBSD). The results showed that Zener–Hollomon parameters obtained from the deformation processes had a significant effect on the dynamic recrystallization and texture of the Mg–6Zn–0.5Ce alloy. The fraction of undynamically recrystallized (unDRXed) regions increased, and the dynamically recrystallized (DRXed) grain size decreased with increasing the Zener–Hollomon parameters. The texture intensity of the DRXed regions was weaker compared with that in the unDRXed regions, which resulted in a sharper texture intensity in the samples deformed with higher Zener–Hollomon parameters. The increase in recrystallized texture intensity was related to preferred grain growth.

Degradation behavior of Mg-4Zn-2Ni alloy with high strength and high degradation rate

To developed a disintegrating fracturing ball used for multi-stage fracturing stimulation, the Mg-4Zn-2Ni alloy was fabricated and subjected to extrusion at the ram speed of 0.1 mm/s in present work. The results indicated that the as-extruded Mg-4Zn-2Ni alloy mainly contained MgZn2, Mg2Ni and MgZnNi (τ) phase. In addition, both the dynamic recrystallized (DRXed) grain size and DRXed ratio increased accompanied with the increasing extrusion temperature. The compressive strength and degradation rate of Mg-4Zn-2Ni alloy extruded at 200 °C were 512.6 ± 4.2 MPa and 619.35 mm/y, respectively, both of which were higher than the current values for Mg alloys of fracturing balls. The results of electrochemical experiments further verified that Mg-4Zn-2Ni alloy extruded at 200 °C has a faster degradation rate. Among the factors that influencing the degradation rate of Mg alloy, the dislocation density and secondary phase were thought as the key role. Galvanic corrosion consisting of the secondary phase and magnesium matrix preferentially occurs in the unDRXed region with high dislocation density. And then corrosion propagate to the DRXed regions.

Effect of micro-alloying Ca on microstructure, texture and mechanical properties of Mg–Zn–Y–Ce alloys

Microstructure, texture and mechanical properties of Mg–5Zn-0.3Y-0.2Ce alloys with the addition of trace xCa (x = 0, 0.3, 0.6 wt%) were systematically investigated in this work. The results revealed that more secondary eutectic phases and smaller grain size of as-cast microstructure could be found with increasing Ca content. After hot extrusion, the Ca-free alloy showed a uniformly recrystallized grain structure, while the Ca-containing alloys possessed a bimodal grain structure composed of fine dynamic recrystallized (DRXed) grains with a size of several microns and un-recrystallized coarse grains. EBSD analysis showed that the three extruded alloys had a fiber texture of (0001) basal plane aligned with the extrusion direction. Texture intensity of the DRXed region was weaker than the deformed region. The extruded alloy with the addition of 0.6 wt% Ca exhibited the highest yield strength of 321MPa due to the smallest DRXed grain size, the deformed region with strong basal texture and dense nanosized precipitates.