Basal Fiber Texture Research Articles

Role of submerged friction stir welding in reducing intermetallic growth and enhancing microstructure in dissimilar Al-Ti joints

The integrity of dissimilar Al-Ti welds during conventional friction stir welding (CFSW) is compromised by excessive material mixing, leading to thick intermetallic layers. Underwater friction stir welding (UWFSW) mitigates these effects by inhibiting material mixing due to lower thermal conditions. Scanning electron microscopy revealed substantial Ti particles, appearing as blocks and strips, within the stir zone during CFSW. Static recrystallization, driven by exothermic reactions between Ti blocks and the Al matrix, resulted in over 93% recrystallized grains along stir zone, 10.7% higher than in UWFSW. In contrast, UWFSW resulted in a finer dispersion of Ti particles with reduced density due to lower frictional heat. The average grain size at the Ti interface of CFSW was 1.0 μm, compared to 2.6 μm in UWFSW. The inhomogeneous distribution of Ti particles in CFSW led to uneven dislocation distribution and increased stress concentrations, while finer Ti particles in UWFSW promoted a uniform grain structure, enhancing joint strength to 267 MPa, 13.4% higher than CFSW. Additionally, the γ-fibre and basal fibre texture in UWFSW increased joint ductility. The study highlights UWFSW’s effectiveness in joining dissimilar metals, offering significant advantages for industries such as aerospace and automotive.

Influence of different wrought processes on the microstructure and texture evolution in AZ31 magnesium alloy

AZ31 magnesium alloys were deformed by five wrought processes (forging, rolling, extrusion, equal-channel-angular-extrusion (ECAE), and caliber rolling) under the condition of an introduced equivalent plastic strain of approximately 1.5 at 573 K. The strain components induced by these wrought processes were computed using the finite element method (FEM). By combining the calculation results with the microstructure observations, the texture and microstructure evolution were discussed from the viewpoint of the strain state. The FEM showed that approximately the same equivalent strain was induced at the center of the alloys where observations were performed. Therefore, as the values of the equivalent plastic strain were fixed in all wrought processes, the effect of the strain component could be compared. The forged and rolled alloys had an intensive basal texture perpendicular to the compression and normal directions, respectively. In the others, a basal fiber texture parallel to the material flow direction was observed. These basal textures were oriented perpendicular to the compressive strain, and their intensities strengthened with an increase in the strain component. The microstructure became more refined and homogenized as the magnitude of the minimum principal strain decreased. This decrease corresponds to the transition of the deformation mode from the uniaxial compression mode to the multidirectional deformation mode as long as the same equivalent strain is induced. This result demonstrates that the microstructure obtained through dynamic recrystallization depends on the deformation mode, separately from the effect of the conventionally reported equivalent plastic strain.

Effects of extrusion temperature on the microstructure and mechanical properties of low-alloyed Mg-Bi-Ca-Mn alloy

A new rare earth-free low-alloyed Mg-0.5Bi-0.8Ca-0.8Mn (wt.%) alloy was prepared at three extrusion temperatures (225, 250 and 275 °C). The effects of low-temperature extrusion on the microstructure and mechanical properties of the alloy were studied. Experimental results show that the dynamic recrystallization (DRX) grains are significantly refined by low-temperature extrusion, and the dynamic recrystallization process is further delayed by the Mn precipitate phase, resulting in a bimodal structure composed of ultrafine DRXed grains and coarse undynamic recrystallized (unDRXed) regions. At an extrusion temperature of 225 °C, the grain size was significantly refined, with an average DRXed grain size of 0.84 μm and a tensile yield strength of 418 MPa. Compared with other extruded magnesium alloys, the ultra-fine DRXed grains, strong basal fiber texture, high Schmid Factors of pyramidal <c + a> slip in the unDRXed regions, and along with a certain amount of second phase (Mg2Ca) distributed along the grain boundaries and nano-Mn particles uniformly distributed in the matrix, are the main reasons for the strength enhancement of low-temperature extruded magnesium alloys. The orientation of the DRXed grains in the alloy after extrusion at 250 °C is more random, which improves ductility. In addition, when the extrusion temperature reaches 275 °C, the alloy shows a fully recrystallized structure and exhibits rare earth (RE)-texture, obtaining high ductility but decreasing strength. This study provides a new idea for the development of high-strength Mg-Bi-based magnesium alloys by adjusting the extrusion temperature and alloying elements. This new high-strength and low-alloyed Mg-Bi-based alloy will help to enrich the series of high-performance, rare-earth free, low-cost extruded Mg alloy with certain application prospects.

Study on microstructure evolution and deformation behavior of Mg– Zn base alloy pipes during hot bending

The strong basal fiber texture of magnesium (Mg) alloy pipes usually leads to poor secondary forming performance. In this study, Mg–2Zn-0.4Ce-0.4Mn (ZME) and Mg–2Zn-0.4Ce-0.4Mn-0.2Ca (ZMEX) pipes were prepared. Compared with the ZME pipe, the ZMEX pipe with a weaker initial texture exhibits excellent bending performance, with a peak load displacement (PLD) of 14.5 ± 0.5 mm and a total energy absorption (TEA) of 142.9 ± 1.7 J. The difference in bending performance between the two pipes is related to the deformation mechanism during hot bending. In the hardening stage, the deformation of the compression zone (CZ) of the two pipes is mainly ETW nucleation, and the overall proportion of twin grains is similar. However, in the tensile zone (TZ), the deformation of the ZME pipe is mainly prismatic slip, while the weak initial texture of the ZMEX pipe leads to the deformation dominated by both prismatic and multiple pyramidal slips, resulting in a higher hardening rate. In the softening stage, the deformation behavior in the CZ and TZ of both pipes tends to be similar. In addition, it is revealed that the softening phenomenon of both pipes after the bending displacement reaches PLD is caused by discontinuous dynamic recrystallization (DDRX) driven by high-density dislocations accumulated in the later CZ and TZ. The research on the microstructure evolution and deformation mechanism of Mg alloy pipe during bending deformation carried out in this study is of great significance for optimizing its secondary forming controllability and further expanding its application.

A method for predicting the yield strength of AZ31 magnesium alloy bars processed by ambient extrusion

Magnesium alloys have strong mechanical properties anisotropy due to their universal basal texture. This study develops a novel method for predicting the yield strength of AZ31 extruded bars with basal fiber texture. From series tensile and compressive tests on ambient extruded bars with different loading direction, the relationship between yield strength, loading direction and extrusion strain was summarized. With varying loading direction, tensile and compressive yield strength can be fitted by linear and nonlinear equations in a strength coordinate system where yield strength can be calculated on different loading direction. Furthermore, parameters of yield strength equations can also be fitted by different equations. Then, from the parameter equations to yield strength equations, tensile and compressive yield strength can be predicted on different loading direction for extruded bars with different extrusion strain.

Developing a high-speed-extruded BMZQ5100 alloy with higher strength and microstructural thermal stability than AZ91 alloy

A new Mg-5Bi-1Mn-0.5Zn-0.2Ag (BMZQ5100, wt%) alloy is developed and analyzed comparatively its extrudability, microstructure, mechanical property and thermal stability with a commercial AZ91 alloy. The results show that the BMZQ5100 alloy can be successfully extruded at a high extrusion speed (ES) of 30 m/min without surface cracks, but there are a large number of hot cracks occurred on the low-speed-extruded AZ91 alloy surface (ES: 5 m/min). For the 30 m/min extruded BMZQ5100 alloy (BMZQ5100-E30), it exhibits a completely dynamic recrystallized (DRX) grain structure with a slightly larger grain size and stronger basal fiber texture than the 2 m/min extruded AZ91 alloy (AZ91-E2) without surface cracks. In terms of second phase, the former alloy contains submicron Mg3Bi2 phases at grain boundaries (GBs), nano-scale Mg3Bi2 and α-Mn particles within grain interiors, along with the co-segregation of Zn and Ag at GBs. The latter alloy has a continuous network of submicron Mg17Al12 phases along GBs, but no any solute segregation is observed at GBs. The BMZQ5100-E30 alloy exhibits more excellent mechanical properties with a tensile yield strength of ∼ 271 MPa, an ultimate tensile strength of ∼ 319 MPa and an acceptable elongation-to-failure of ∼ 8%, compared with the AZ91-E2 alloy. The GB strengthening, precipitation strengthening and solute segregation strengthening on the TYS occupy ∼ 46.2, ∼ 45.5 and ∼ 8.3%, respectively. In addition, the BMZQ5100-E30 alloy has higher microstructural thermal stability than the AZ91-E2 alloy, because of second phase pinning and solute segregation at GBs to effectively inhibit the grain growth during annealing.

Extrusion limit diagram of Mg–5Bi–3Al–1Zn alloy and effects of extrusion parameters on its microstructures and mechanical properties

Hot-compressive tests and finite element simulations were carried out to construct an extrusion limit diagram of a Mg–5Bi–3Al–1Zn (wt.%) alloy in this work. It was observed that 310 °C became a dividing line, below which the safe extrusion zone was narrow because the stress required to induce the plastic flow of alloy was higher than the pressure limit. Once the temperature exceeded this critical temperature, a wide safe extrusion zone controlled by the cracking limit was attained. The theoretical maximum ram extrusion speed was calculated as approximately 48 mm/s at 310 °C. No hot cracks occurred on the surface of alloys extruded at 30 and 44 mm/s; while at 56 mm/s, obvious orange peel defects were observed. Through further microstructural observation, the 44 mm/s extruded alloy exhibited a complete dynamic recrystallization structure with an average grain size of 21.9 μm, along with a relatively weak basal fiber texture (with a maximum pole intensity of 5.8) and plentiful nano-Mg3Bi2 phases. These microstructure features led to superior tensile properties (namely a tensile yield strength of 270 MPa, an ultimate tensile strength of 375 MPa and an elongation of 15%) at the high-speed extrusion.

Texture weakening and grain refinement behavior of the extruded Mg-6.03Zn-0.55Zr alloy during hot plane strain compression

A series of hot plane strain compression (PSC) experiments of the extruded Mg-6.03Zn-0.55Zr alloy were conducted on the Gleeble-3500 machine with strain rates of 0.01 s−1 to 10 s−1 and temperatures ranging from 300 °C to 500 °C to reveal the microstructure evolution during the secondary process. The effects of grain refinement and texture modification which were easily affected by the deformation mechanism and dynamic recrystallization (DRX) were systematically studied. Experimental results showed that the main deformation mechanism during PSC was basal <a> slip (74.3 %–94.9 %) and assisted by prismatic <a> slip (4.8 %–21.1 %) and pyramidal <c+a> slip (0.3 %–4.6 %). Since the pyramidal <c+a> slip and prismatic <a> slip were more preferred to activate owing to the significant decrease of critical resolved shear stress (CRSS) at a higher temperature, the activation of non-basal slip promoted the c-axes of the grains deviated from compression direction which weakened the basal fiber texture. Moreover, the activation of non-basal slip could promote DRX behavior to some extent. Further analysis of the DRX mechanism showed that the continuous DRX (CDRX) by continuous rotation of low angle grain boundaries was dominant at lower temperatures and higher strain rates, while discontinuous DRX (DDRX) which nucleated at the grain boundaries played a more and more important role as the temperature increased and strain rate decreased. After characterizing the orientations of the DRXed grains, the CDRXed grains owned a similar grain orientation with the deformed grain while the DDRXed grains exhibited a fairly dispersed distribution, indicating that the weakening effect of the basal texture was greater with a higher DDRX fraction.

Enhancing Microstructural, Textural, and Mechanical Properties of Al-Ti Dissimilar Joints via Static Shoulder Friction Stir Welding

Abstract The present study explores the application of static shoulder friction stir welding (SSFSW) to address the challenges of poor mechanical properties in conventional Al-Ti dissimilar friction stir joints, which arise due to significant material mixing and the formation of thick intermetallic layers. The results show that SSFSW inhibited material mixing and the mutual diffusion of Al and Ti were suppressed due to lower heat input. Mutual interdiffusion of Al and Ti was directed by an exothermic chemical reaction, forming an Al5Ti2 – Al3Ti sequence due to sluggish diffusion of Al in Ti at a temperature of 512°C achieved in this study. The microstructure at stir zone (SZ) comprised equiaxed grains with Ti particles acting as dispersoids for nucleation, whereas the presence of large Ti blocks at SZ of Conventional FSW (CFSW) resisted plastic deformation, resulting in non-homogeneous concentration of dislocations near its interface. A significant decrease in grain size at all the critical zones of weldment was due to rearrangement of dislocations through slip-and-climb mechanism, as evidenced by the occurrence of dynamic recrystallization. Emergence of γ-fiber and basal fiber texture increased the tensile strength of SSFSW to 289 MPa, which is about 11.2% higher than CFSW, with joint efficiency of about 88%. The study also analysed the contribution of various strengthening mechanisms to the yield strength improvement of SSFSW weldments in detail of SSFSW weldments in detail, and the results showed that grain boundary strengthening contributed the most to strength improvement in SSFSW.

Enhanced strength-ductility synergy of β-solidifying TiAl alloy with preferred lamellar orientation by texturing high-temperature α phase through hot extrusion

A preferentially-aligned lamellar structure in TNM alloy with enhanced strength-ductility synergy is successfully obtained by texturing the high-temperature α phase through hot extrusion. The lamellar orientations of the resultant lamellar colonies inherit the texture feature of the extruded high-temperature α phase ({0001} basal fiber texture), exhibiting a preferential distribution with 60% of the lamellar traces {0001}α/{111}γ nearly parallel to the extrusion direction (ED). The influence of the microstructural variables on the deformation mechanisms and fracture mechanisms are elucidated by microstructural characterization and crystallographic analysis. Results show that when the lamellar trace is parallel to the tensile direction (TD//ED), twinning and stacking faults in the γ laths are favorable to be activated. The origin of the enhanced strength-ductility synergy is attributed to the combined effects of twinning, stacking faults and its induced dislocation slip, as well as the extra interaction stresses introduced by the multiple deformation mechanisms and the α2/γ interfaces. This study can provide a novel strategy for microstructural regulation and design of high-performance β-solidifying TiAl alloys.

Achieving high strength near 400 MPa in an ultra-fine grained Mg–Bi–Ca ternary alloy via low-temperature extrusion

Significantly enhancing the mechanical properties of Mg–Bi base series alloys is of great significance for their wider application prospects. Here, a new Mg–3Bi–1Ca (BX31, wt.%) alloy showing high tensile yield strength of ∼397.1 MPa, high ultimate tensile strength of ∼416.2 MPa and acceptable elongation of ∼8% was fabricated by low-temperature extrusion. The analysis of microstructure showed that the enhanced yield strength was attributed to the ultra-fine grain structure (∼0.84 μm), nano-scale second phases including Mg2Bi2Ca and Mg2Ca, and Ca segregation at grain boundaries. In addition, a weak basal fiber texture to some extent provided more basal slip activities, guaranteeing the suitable ductility. The dynamic recrystallization and dislocation behavior of the BX31 billet during extrusion were also systematically observed and discussed to reveal the formation mechanisms of the ultra-fine grain structure with the weak basal fiber texture in the as-extruded BX31 alloy. As mentioned above, this work offers a new insight to obtain high-performance Mg–Bi base series alloys.

Development of ultrahigh-strength low-alloy Mg-0.7Al-0.3Ca-0.4Mn (wt.%) alloy with excellent ductility via controlling extrusion temperature

Mg-0.7Al-0.3Ca-0.4Mn (AXM070304, wt.%) alloy was subjected to extrusion with a ram speed of 1 mm/s and an extrusion ratio of 25:1. The extrusion temperature varies from 170 °C to 400 °C. The influence of extrusion temperature on microstructure and mechanical properties of the dilute AXM070304 alloy was systematically explored. With raising the extrusion temperature, the average size of the dynamic recrystallized (DRXed) grains was increased, while the intensity of the basal fiber texture was decreased. When the extrusion temperature was escalated from 170 °C to 400 °C, the tensile yield strength (YS) of the low-alloy AXM070304 extrusion alloy was decreased from 437 to 246 MPa, while the elongation to failure (EL) was increased from 2.9 to 16.9%. The alloy extruded at 200 °C obtains an YS of 412 MPa, an ultimate tensile strength (UTS) of 418 MPa and an EL of 14.8%, exhibiting excellent ductility and ultrahigh strength. The ultrahigh YS was mainly due to the strengthening from ultra-fine recrystallized grains (0.61 μm) with grain boundary segregation of solute Al and Ca atoms. The growth of DRXed grains was inhibited mainly by the co-segregation of Al atoms and Ca atoms, nanosized Al2Ca and β-Mn particle phases at the grain boundaries. Plastic instability occurred under tensile loading in the ultrafine-grained AXM070304 alloy, which may be due to the fact that the grain boundary segregation of Al atoms and Ca atoms requires a high energy barrier for dislocation emission. Once the tensile stress reaches the peak value, the mobile dislocation density increases suddenly.

In situ analysis of phase constituents evolution upon hydrogen cycling of cold-forged Mg-Ni powders

Development of hydrogen storage in metal hydrides requests efficient, simple and safe processes such as room temperature forging. Samples elaborated in this way from Mg and Ni powders result in bulk pellets whose only identified phases are Mg and Ni. Deuterium absorption occurs from 250 °C in these samples due to the co-existence of basal fiber texture and structural defects, both induced by forging. In situ neutrons diffraction analysis shows the progressive formation of the Mg2NiD0.3 / Mg2NiD4 phases upon deuterium cycling and allows to identify the multi-step absorption and desorption mechanisms at temperatures as low as 270 °C. The growth of the Mg2NiD0.3 / Mg2NiD4 phases occurs in a short time during the second step of the deuterium absorption – as Mg2NiD0.3 transformed into Mg2NiD4 – and progresses from the periphery of the initial Ni particles towards their center. The mechanism is controlled simultaneously by deuterium diffusion and migration of Mg atoms through the already formed Mg2NiD4 deuteride. The reaction between Mg and Ni is not observed in the absence of deuterium, even after annealing at 285 °C for 48 h, thus we evidence a deuterium-induced mobility of the metal atoms.

The influence of the LPSO on the deformation mechanisms and tensile properties at elevated temperatures of the Mg-Gd-Zn-Mn alloys

The introduction of long period stacking ordered (LPSO) phase is an effective way to improve the performance of the magnesium alloys at elevated temperatures. In this paper, the hot tensile behaviors of two Mg-4Gd-1Zn-0.5Mn (wt.%) alloys with different lamellar LPSO volume fractions under the strain rate of 2.2 × 10–4 s –1 and at varied temperatures (150 °C–250 °C) were investigated. With the increasing of the deformation temperatures, the peak stresses of the alloy with lower volume fraction of the LPSO decreased (denoted as LL alloy). The hot tensile mechanical properties of the alloy with higher volume fraction of the LPSO (denoted as HL alloy) are significantly higher than those of LL alloy. When the deformation temperature was 250 °C, the LL alloys significantly underwent dynamic recrystallization (DRX) and the DRX dominated by discontinuous dynamic recrystallization (DDRX). However, the HL alloys did not have obvious DRX due to the lamellar LPSO hindering the grain boundary migration. The basal fiber texture of the alloy was produced after hot tensile. The deformation of the LL alloys was dominated by prismatic <a> slip during the hot deformation while the deformation of the HL alloys was dominated by the prismatic <a> slip and pyramidal <c+a> slip. The pyramidal <c+a> slip was activated by the Young's moduli mismatch between the α-Mg matrix and LPSO. Lamellar LPSO has an positive effect on strengthening the mechanical properties of the alloy which is attributed to the hinder of LPSO to non-basal slip, the prick function of kink to basal slip and the inhibition of LPSO to DDRX.

The microstructural features and strengthening mechanisms of Mg-Al-Zn-Ca-(RE) extruded alloys having high-volume fractions of second-phase particles

The microstructures and tensile properties of Mg-4∼6Al-2∼4Zn-2∼3Ca-0∼1RE (in wt.%) extruded alloys have been investigated. C15 and C36 Laves phases, Ca2Mg6Zn3, Al2REZn2, and Al11RE3 phases were formed as networks during solidification in different alloys. After extrusion, coarse dendritic were significantly refined due to dynamic recrystallization, second phases were fragmented into pieces arranged as stripes, and typical basal fiber texture {0002} <10-10> with the extrusive direction paralleled to (0001) were formed in all studied alloys. Laves phase particles were prone to be crushed into nanoparticles, which appeared more easily to hinder the recrystallized grain growth and could bring about more than 30 vol % ultra-fine grains after extrusion. During extrusion, twinning-induced dynamic recrystallization occurred at first, and both discontinuous and continuous dynamic recrystallization dominated the microstructural evolution. The volume fraction of second phases had critical roles in recrystallization process, and a nearly complete recrystallization degree could be obtained in alloys containing more than 9 vol% second phases. The strengthening mechanisms were evaluated based on classic strengthening models, which agreed well with the experimental results. It was found that grain boundary strengthening, second phase strengthening, and texture strengthening contributed around 60%, 30%, and 10%, respectively, to yield strengthening, except for Mg-4Al-4Zn-2Ca alloy because of the high percentage of unrecrystallized region. Moreover, the overestimate of second phase strengthening happened in alloys having more than 9 vol% second phases, which revealed that too many second phases had limited influence on microstructures and the resulting mechanical properties.

Role of extrusion rate on the microstructure and tensile properties evolution of ultrahigh-strength low-alloy Mg-1.0Al-1.0Ca-0.4Mn (wt.%) alloy

Mg-1.0Al-1.0Ca-0.4Mn (AXM1104, wt.%) low alloy was extruded at 200 °C with an extrusion ratio of 25 and different ram speeds from 1.0 to 7.0 mm/s. The influence of extrusion rate on microstructure and mechanical properties of the AXM1104 alloy was systematically studied. With the increasing of extrusion rate, the mean dynamically recrystallized (DRXed) grain size of the low alloy and average particles diameter of precipitate second phases were increased, while the degree of grain boundary segregation and the intensity of the basal fiber texture were decreased. With the rising of extrusion rate from 1.0 to 7.0 mm/s, the tensile yield strength (TYS) of the as-extruded AXM1104 alloy was decreased from 445 MPa to 249 MPa, while the elongation to failure (EL) was increased from 5.0% to 17.6%. The TYS, ultimate tensile strength (UTS) and EL of the AXM1104 alloy extruded at the ram speed of 1.5 mm/s was 412 MPa, 419 MPa and 12.0%, respectively, exhibiting comprehensive tensile mechanical properties with ultra-high strength and excellent plasticity. The ultra-high TYS of 412 MPa was mainly due to the strengthening from ultra-fine DRXed grains with segregation of solute atoms at grain boundaries. The strain hardening rate is increase slightly with increasing extrusion speed, which may be ascribed to the increasing mean DRXed grain size with rising extrusion speed. The higher strain hardening rate contributes to the higher EL of these AXM1104 samples extruded at higher ram speed.

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.

Microstructures and mechanical properties of Mg–5Li–4Sn–2Al–1Zn alloy after hot extrusion

In this work, Mg–5Li–4Sn–2Al–1Zn deformed magnesium alloy was prepared and the effects of the extrusion process on its microstructure, texture evolution, and mechanical properties were investigated. The microstructures of as-homogeneous and as-extruded alloys were characterized by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that the alloy underwent dynamic recrystallization (DRX) after hot extrusion processes. Drastic refinement occurred in grain size, and the weakening of the basal fiber texture was obvious after the Forward-Parallel Channel Extrusion process, and the microstructure was more uniform. As a result, the mechanical properties of the alloy were superior after the Forward-Parallel Channel Extrusion process, and the best combination of strength and plasticity was obtained after the 105° FPE process. YS, UTS, and EL were 187 MPa, 275 MPa, and 15%, respectively. The increase in strength is mainly attributed to grain boundary strengthening and the pinning effect of shattered particles on the migration of dislocations and grain boundaries. The increase in plasticity can be explained by the activation of non-basal slip and the weakening of the basal fiber texture, the fine grains can coordinate the plastic deformation well and improve the plasticity of the alloy to some extent.

Variations in dynamic recrystallization behavior and mechanical properties of AZ31 alloy with extrusion temperature

This study investigates the effects of extrusion temperature on the dynamic recrystallization (DRX) behavior of a Mg–3Al–1Zn–0.3Mn (AZ31, wt%) alloy during hot extrusion and on the microstructural characteristics and mechanical properties of materials extruded at 350 and 450 °C. An increase in the extrusion temperature causes a decrease in the amount of strain energy accumulated in the material during extrusion, because of promoted activation of pyramidal <c + a> slip and dynamic recovery. This reduced strain energy weakens the DRX behavior during extrusion, which eventually results in a decrease in the area fraction of recrystallized grains of the extruded material. The material extruded at 450 °C has coarser grains and a stronger basal fiber texture than that extruded at 350 °C. As the extrusion temperature increases from 350 to 450 °C, the tensile yield strength (TYS) of the extruded material increases from 191.8 to 201.5 MPa, whereas its compressive yield strength (CYS) decreases from 122.5 to 111.0 MPa; consequently, its tension–compression yield stress ratio (CYS/TYS) decreases from 0.64 to 0.55. The increase in the TYS is attributed mainly to the stronger texture hardening and strain hardening effects of the extruded material, and the decrease in the CYS is attributed to the reduced twinning stress resulting from grain coarsening and texture intensification. The microstructural and textural evolutions of the materials during extrusion and the deformation and hardening mechanisms of the extruded materials are discussed in detail.

Microstructures, mechanical properties and degradability of Mg-2Gd-0.5(Cu/Ni) alloys: A comparison study

Low alloying Mg-2Gd-0.5(Cu/Ni) alloys for sealing tools in the oil and gas industry were prepared. The differences in the effects of minor Cu and Ni additions on microstructures and properties of the Mg-2Gd alloy were compared. The results showed that adding Ni was more effective than adding Cu in refining grain sizes, strengthening the basal fiber texture, and promoting the formation of LPSO phases, resulting in higher strength. The tensile yield strength/elongation of the Mg-2Gd-0.5Cu alloy, Mg-2Gd-0.25Cu-0.25Ni alloy, and Mg-2Gd-0.5Ni alloy was 146 MPa/23.7%, 175 MPa/23.1%, and 248 MPa/18.2%, respectively. The decreased elongation was attributed to the basal fiber texture and the presence of coarse LPSO phases. In terms of the corrosion rate in 3.5 wt.% NaCl solution, it rose from 112 mm y–1 for the Mg-2Gd-0.5Cu alloy to 269 mm y–1 for the Mg-2Gd-0.25Cu-0.25Ni alloy and 490 mm y–1 for the Mg-2Gd-0.5Ni alloy, indicating that the addition of Ni instead of Cu showed a more significant promoting effect on the degradability of Mg alloys, which was related to more refined grains, the stronger basal fiber texture, and a larger amount of LPSO phases.