Mg17Al12 Phase Research Articles

The effect of Mg17Al12 intermetallic compound on dynamic recrystallization of cast-forged AZ80 magnesium alloy

An asymmetric I-crossbeam geometry is produced by cast-forging of the AZ80 magnesium alloy at two different casting cooling conditions and three different forging temperatures. Samples are extracted from two different locations from each component, representing different deformation conditions, for microstructure study. This paper presents a detailed investigation into the relationship between the Mg17Al12 intermetallic compound and dynamic recrystallization in the cast-forging process. The eutectic, lamellar, discontinuous, and continuous morphologies of the Mg17Al12 phase are observed in the produced components, and their evolution during the cast-forging process is investigated. Depending on the forging condition, dissolution and re-precipitation of the Mg17Al12 phase might occur before or after the forging stage and influence the extent, distribution, and grain size of DRX. It is shown that the eutectic, lamellar, and discontinuous morphologies of the Mg17Al12 phase effectively promote dynamic recrystallization. On the other hand, the continuous morphology is only effective when the particles are broken as a result of high deformation. This study provides a better understanding of the effect of Mg17Al12 intermetallic compound on the hot deformation behavior of the AZ80 alloy, which can be used to tailor the cast material in order to improve the forgeability and final mechanical properties of the magnesium-based structural components.

Nanocrystallization and precipitation behavior evolution of AZ80 magnesium alloy during multi-directional compression

In response to the growing demand for high-performance magnesium alloys in the aerospace and transportation industries, researchers conducted a study on the AZ80 magnesium alloy. The primary objective was to achieve a nanocrystalline structure in the alloy through severe plastic deformation using low-strain multi-directional compression at room temperature. Subsequently, an aging treatment was performed to induce the transformation of the structure into a stable state. The study aimed to investigate the morphology and mode of the second phase precipitation in the magnesium alloy after undergoing severe plastic deformation. The research findings revealed that the application of multi-directional and multi-pass compression during room temperature deformation of the magnesium alloy effectively prevented instability and fracture. Moreover, this process facilitated the accumulation of larger true strain. As the number of compression passes increased, deformation twins became increasingly denser, particularly in the intersecting areas. Consequently, ultrafine high-angle grain structures were preferentially formed in these regions. Furthermore, the number of fine-grained areas gradually increased with each deformation pass. After ΣΔε 5.12, the grain size was refined to a range of 100–200 nm. Additionally, the aging treatment following severe plastic deformation brought about a significant change in the traditional lamellar precipitation mode of the second phase Mg17Al12 in the magnesium alloy. Instead, spherical precipitation occurred.

Microstructural evolution mechanism and mechanical properties of La and Gd on AZ91 alloy: Experiments and first-principles calculations

The morphology and thermal stability of the Al-RE phase in Mg-Al-RE alloys are critical to their mechanical properties, particularly at elevated temperatures. In this study, AZ91, AZ91–2La, and AZ91–2La-0.6Gd alloys were prepared via gravity casting and characterized using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicate that adding La reduces the amount of the Mg17Al12 phase and introduces a long acicular Al11La3 phase. Further addition of minor amounts of Gd transforms the long acicular Al11La3 phase into a short rod-like Al11RE3 phase. Tensile tests and fracture analyses at both room and elevated temperatures reveal that the AZ91–2La-0.6Gd alloy exhibits exceptional tensile properties. First-principles calculations were used to study the modification mechanism of Gd atoms on the Al11La3 phase. Adsorption calculations show that Gd atoms stably adsorb on the Al11La3 (001) growth surface, altering its growth characteristics. These calculations also investigated the thermal stability and formation enthalpy of intermetallic phases in Mg-Al-La-Gd alloys. Additionally, the complex alloying reactions during the solidification of the Mg-Al-La-Gd multi-element alloy system were simplified. This study provides new insights into the interaction mechanisms of rare earth (RE) elements in Mg-Al series alloys. It also offers a new approach for designing heat-resistant Mg-Al-RE alloys.

Effect of cryogenic temperature on the strengthening mechanisms of AZ61 Mg alloy extruded at different temperatures

This study investigates the influence of extrusion and deformation temperatures on the mechanical properties of the AZ61 Mg alloy. Increasing the extrusion temperature from 300 to 400 °C led to larger grain size and higher basal texture intensity. At 400 °C, the AZ61 alloy exhibited more Al–Mn phases and fewer Mg17Al12 phases, indicating enhanced dissolution of Mg17Al12 in the α-Mg matrix. Uniaxial tensile tests were conducted at room temperature (RT) and cryogenic temperature (CT, −150 °C). Despite grain growth, a higher yield strength (YS) was achieved at higher extrusion temperatures due to the texture-strengthening mechanism. However, during deformation at CT, the higher YS was primarily attributed to the formation of multiple twinning within individual grains, causing twinning interactions. These twin-interacting boundaries create additional barriers to dislocation movement. Notably, the AZ61 sample extruded at 400 °C demonstrated the formation of stacking faults during deformation at CT, with dislocations accumulating around the faults. This contributed to the best strength without compromising ductility in this sample.

The influence of Zn addition on the microstructure and mechanical and corrosion properties of warm rolled Al[sbnd]Mg alloys containing Er and Zr

The effects of a minor Zn addition on the mechanical and corrosion properties and microstructure of a high Mg content AlMg alloy containing Er and Zr in the warm-rolled state were studied using tensile test, nitric acid mass loss test (NAMLT), exfoliation corrosion susceptibility test (ASSET), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The tensile test results showed that the 0.58 wt% Zn addition to the Al-Mg-Er-Zr alloy increased the yield strength from 297 to 351 MPa and tensile strength from 416 to 445 MPa, but decreased the elongation from 13.3 % to 12.5 %. The NAMLT and ASSET results showed that the two warm rolled alloys were initially in the stabilization state, but the Al-Mg-Er-Zr alloy without Zn added became sensitized severely after the accelerated sensitization annealing (ASA) at 100 °C. The Zn addition improved the intergranular corrosion (IGC) resistance and exfoliation corrosion (EC) resistance significantly. The TEM results showed that, for the Al-Mg-Er-Zr alloy, there were Al3(Er,Zr) phase particles in the matrix and β (Al3Mg2) phase particles separated from each other at the grain boundary. After the ASA treatment, more β phase particles were precipitated and covered the grain boundary completely. For the Al-Mg-Zn-Er- Zr alloy, another nanoscale T (Al32(Mg, Zn)49) phase was precipitated in the matrix, and there were no grain boundary phase particles observed at the grain boundary, because the precipitation of T phase consumed the supersaturated Mg in the matrix, thus suppressing the formation of grain boundary phase particles during the ASA treatment and resulting in a good corrosion resistance. The strengthening effect of the Zn addition was mainly due to the formation of T phase particles during the warm rolling process.

Revealing the heterogeneous nucleation mechanism of Mg17Al12 on impurity Mg2Si particles in commercial AZ31 alloy

Silicon (Si) is an inevitable impurity element in the AZ31 alloy. In this study, the Si impurity was detected mainly as fine Mg2Si particles dispersed widely within the central region of the Mg17Al12 phase. During the solidification process, the Mg2Si particle precipitates at about 565 °C, before the Mg17Al12 phase of 186 °C, potentially acting as the heterogeneous nucleation core for the Mg17Al12 phase. The orientation relationship between Mg2Si and Mg17Al12 was investigated using the edge-to-edge matching model (E2EM) calculations, which showed a misfit of only 0.1 %. This low misfit suggests that Mg2Si can serve as a heterogeneous nucleation site for Mg17Al12. The surface and interface structures of Mg2Si (220) and Mg17Al12 (332) were constructed, and then investigated through the first-principles calculation. The theoretical results indicate that Mg and Al are easily adsorbed on the surface of Mg2Si, with Al showing higher adsorption energy than Mg. Furthermore, the interface between Mg2Si and Mg17Al12 exhibits favorable thermodynamic stability. Combined with experiments and theoretical calculations, it is confirmed that the Mg2Si particles, formed due to the Si impurity, provide effective heterogeneous nucleation sites for the Mg17Al12 phase.

Microstructure Evolution and Creep Properties of AZ61 Magnesium Matrix Composites Reinforced with Bimodal-Sized SiC Particles

In the scope of this exploration, AZ61 magnesium matrix composites fortified with bimodal size SiC particles were synthesized using ultrasonic-assisted mixing in the semi-solid state, which exhibited optimal grain refinement and exceptional creep resistance. We examined the impact of bimodal SiC particles on the microscopic structure and creep deformation of the resulting composites. Our findings indicated that incorporating bimodal SiC particles resulted in the refinement of the matrix grains and alteration of the morphology of the Mg17Al12 phase. Furthermore, the micron-sized SiC particles exhibited a typical necklace-like particle distribution around the grain boundaries of the bimodal SiC particle/AZ61 composites, while the nano-sized SiC particles were mainly located around the micron-sized particles. As the volumetric percentage of micron SiC particles increased, the quantity of nano-sized particle clusters diminished noticeably. Creep analysis at 200 °C and 50 MPa revealed that the creep life of M−6+N−1 composite was increased by 111.9% compared to the AZ61 alloy. Additionally, the M−6+N−1 combination exhibited a significantly lower steady-state creep rate compared to the matrix alloy, with a reduction of approximately 11 times. These results indicate that the bimodal SiC particle/AZ61 composites have superior creep resistance, which is a consequence of the grain refinement and grain boundary pinning effects of SiC particles.

Microstructure and Mechanical Properties of Mg-Al-La-Mn Composites Reinforced by AlN Particles.

The Mg-Al-RE series heat-resistant magnesium alloys are applied in automotive engine and transmission system components due to their high-temperature performance. However, after serving at a high temperature for a long time, the Al11RE3 phase coarsened and even decomposed, while the Mg17Al12 phase grew and dissolved, which limits the service temperature of Mg-Al-RE series heat-resistant magnesium alloys to a maximum of 175 °C. In this study, a new preparation method for in situ AlN particles was presented. The AlN/Mg-4Al-4La-0.3Mn composites were prepared by a master alloy and casting method. The effects of various contents of AlN (0.5-3.0 wt.%) on the microstructure and mechanical properties of the Mg-4Al-4La-0.3Mn (AE44) alloy at room (25 °C) and high temperatures (150-250 °C) were investigated. Microstructure analysis revealed that the inclusion of AlN led to a reduction in both the grain size and second phase size in the AE44 alloy, while also improving the distribution of the second phase. The average grain size, Al11La3 phase, Al2La phase, and Al3La phase of the 2.0 wt.% AlN/AE44 composite were 135.7, 9.6, 1.9, and 12.6 μm, respectively, which were significantly lower than those of the AE44 matrix alloy (179.8, 12.6, 3.3, 17.8 μm). The refinement was attributed to the ability of AlN particles to serve as heterogeneous nucleation cores for α-Mg and, at the same time, impede the growth of the solid-liquid interface, eventually leading to grain refinement. With the increase in the AlN content, the mechanical properties of composites initially exhibited an increase at both room and high temperatures, followed by a subsequent decrease. When the AlN content was 2.0 wt.%, the composite exhibited optimal strength and plasticity matching. At room temperature, the TYS, UTS, and EL values of the 2.0 wt.% Mg-4Al-4La-0.3Mn composite were 96 MPa, 175 MPa, and 7.0%, respectively, which were increased by 26 MPa, 27 MPa, and 0.7% when compared with the base alloy. The TYS of the 2.0 wt.% Mg-4Al-4La-0.3Mn composite at 150 °C, 200 °C, and 250 °C were 17 MPa, 14 MPa, and 22 MPa higher than those of the matrix alloy, respectively. The main strengthening mechanisms were second phase strengthening, load transfer strengthening, and thermal mismatch strengthening. At elevated temperatures, AlN particles effectively pinned the grain boundaries, inhibiting their migration, and hindered dislocation climbing, resulting in excellent mechanical properties of the composites at high temperatures. This study contributes to the advancement of in situ AlN particle preparation methods and the exploration of effects of AlN on the properties and microstructure of Mg-Al-RE alloys at high temperatures (150-250 °C).

Improving intergranular cracking and stress corrosion cracking resistance of highly sensitized AA5083 Al-Mg alloy via reversion heat treatment

This study systematically examines the impact of reversion heat treatments (220–280 ℃ for 1 h) on the microstructure evolution, electrochemical corrosion, intergranular cracking (IGC) and stress corrosion cracking (SCC) of a severely sensitized (175 ℃/100 h) AA5083 alloy. Increasing the reversion temperature gradually enhances the corrosion resistance by dissolving the β′-Al3Mg2 phase, with the optimal treatment identified as 280 ℃/1 h. The βˊ phase maintains its planar film shape and continuously covers the grain boundaries after reversion treatment below 240 °C, but spheroidizes at the triple junctions at 260 °C. The morphology of the βˊ phase is dictated by grain boundary diffusion and interface diffusion. Reversion treatments improve SCC resistance by dissolving the β′ phase and reducing yield strength, attributed to anodic dissolution and hydrogen embrittlement mechanisms. This research offers valuable insights into the practical benefits of reversion treatments for Al-Mg alloy marine applications, addressing safety concerns related to sensitization.

Enhancing the mechanical properties and thermal conductivity of Ti/AZ91 composites through integrated extrusion and rolling continuous deformation processing

With the increasing demand for highly integrated circuits to optimize energy efficiency, reduce weight, and improve mechanical properties, finding a Magnesium (Mg) matrix material with excellent mechanical strength and high thermal conductivity poses a significant challenge. In this work, titanium (Ti) particles were introduced into AZ91 (Mg-9Al-1Zn) alloy to fabricate Ti/AZ91 composites, employing a combination of stir casting, extrusion and rolling processes. This strategy simultaneously enhances the mechanical properties and thermal conductivity of the Ti/AZ91 composites compared with AZ91 alloy. The incorporation of Ti particles serves to refine grains, expediting the formation of Mg17Al12 phase within the Mg matrix. Optimal comprehensive mechanical properties are attained in 10 wt% Ti/AZ91 composite, exhibiting an ultimate tensile strength of 365 MPa, an elongation of 11.9 %, and a significantly low wear rate of 4.548×10−3 mm3/m. Notably, the 10 wt% Ti/AZ91 composite shows a 41.1 % reduction in wear rate relative to the AZ91 alloy, attributed to the incorporation of hard Ti particles. Furthermore, the thermal conductivity of the 2.5 wt% Ti/AZ91 composite exhibits a significant enhancement over that of the AZ91 alloy. Detailed discussions are provided on the fundamental mechanisms responsible for strengthening, wear resistance, and thermally conductive in Ti/AZ91 composites. These results highlight the substantial potential of Ti/AZ91 composites for lightweight structural applications, such as highly integrated circuits requiring excellent mechanical properties and high thermal conductivity.

Second phase and matrix texture evolution influence mechanical properties of Al-Mg-Al composite plate by HPR with annealing temperature

Annealing treatment can determine the quality of heterogeneous composite plate by regulating the matrix and interface structures and interlayer bonding ability. Al-Mg-Al composite plate was used as an example. Al-Mg-Al composite plate was rolled with 50 % reduction by hard plate rolling. After that, it was annealed at 250 ℃, 300 ℃, 350 ℃ and 400 ℃ for one hour respectively. Through microstructure observation and performance test, the results show that the reaction phases of Al3Mg2 and Al12Mg17 were formed at the interface during annealing treatment. As the temperature continued to climb, yield strength and elongation after fracture of Al-Mg-Al composite plate showed a trend of increasing first and then decreasing, in addition, the tensile strength gradually decreased. As temperature reached 300 °C, its performance reached the best, the tear strength increased to 0.367 KN, and yield strength and elongation reached 172 MPa and 14.5 %, respectively. The study showed that although annealing temperature didn't change types of texture configuration of magnesium alloy, it affected the grain growth, resulting in the change of base surface texture and the overall performance of heterogeneous composite plate. This research provides a theoretical basis for precise regulation of microstructure and comprehensive performance of heterogeneous composite plate by annealing treatment.

A comprehensive investigation of alloying elements on site preferences, elastic properties and electronic structure of Mg17Al12 by first-principles calculations

The effect of elemental doping on the site preference, elastic properties and electronic structure of Mg17Al12 has been systematically investigated by first-principles calculations. And twenty-seven elements (Li, Na, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Sr, Y, Zr, Ag, Cd, In, Sn, Sb, Pb, Bi and La) are considered in this study. The calculations of substitution formation energies indicate that the alkali metal (Li), alkaline earth (Ca, Sr) and rare earth (Sc, Y, La) group elements and Ti, Zr favor to occupy Mg sites, and transition group (Fe, Co, Ni, Cu, Ag, Zn, Cd) elements and Ga, Ge, Sn, Sb prefer to occupy Al site, while Na, K, V, Cr, Mn, In, Pb and Bi are unstable in Mg17Al12 phase. Meanwhile, the results of phonon dispersion curves for the preferentially doped systems show that all doped structures are dynamically stable except for Sr, La and Sn doped systems. The elastic constants indicate that all preferential doping models are mechanically stable, and solute atoms with high bulk modulus lead to an increase in the bulk modulus of Mg17Al12 phase. Simultaneously, the calculated shear modulus/bulk modulus ratio (G/B), Poisson's ratio (v) and Cauchy's pressure (C‾12‐C‾44) indicate that the ductility of doped systems is better than Mg17Al12 alloy. All structures are elastic anisotropic, while the doping of Fe, Co and Ni reduces the degree of anisotropy of Mg17Al12 phase. Furthermore, the electronic structures show a strong hybridization between the p-orbitals of Mg and Al and the d-orbitals of alkaline earth, rare earth and Zr elements, resulting in higher structural stability. Finally, the adsorption behavior of O atom on Mg17Al12(110) surface and the structural stability, lattice constants, and elastic modulus of Mg34Al24-xZnx random solid solution alloys are investigated.

Fatigue crack growth study on rolled and cryogenically treated AZ31B Mg alloy plate

This paper investigates the fatigue crack growth rate (FCGR) of AZ31B Mg alloy after cryogenic treatments. Shallow and deep cryogenic treatments were carried out separately at −80οC and −196οC for 12 and 72 hrs, respectively. The microstructural characterization of the cryogenically treated AZ31B specimens was carried out by optical microscope (OM) and X-Ray diffraction (XRD). The small crystalline size structure generated in AZ31B alloy due to the cryogenic treatment further promoted the nucleation of Mg17Al12 phase. Accumulation of dislocation density was also observed in the cryogenically treated specimens. CT specimens were prepared for all three conditions to estimate the FCGR. The as-rolled specimen (R) had higher fatigue resistance than the cryogenically treated specimens. The R specimen’s threshold intensity factor (ΔKth) was higher than the cryogenically treated specimens. The exponent (m) value of the R specimen was lower than the shallow and deep cryogenic treated specimens. Hence, the crack growth resistance was marginally higher in the R specimen compared to the cryogenically treated specimens. However, the critical stress intensity factor (ΔKcr) of cryogenically treated specimens was slightly higher than the R specimen. The post-fracture characterization of the specimens was carried out at three different regions by SEM. The cleavage faces, tear ridges, and voids were noticed in all specimens. The fatigue failure of the R specimen was due to ductile and brittle mode, whereas the cryogenically treated specimen was dominated entirely by brittle fracture.

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.

Development of highly corrosion-resistant Mg-Al-Y extruded alloy via regulating the Mg17Al12 phase

A highly corrosion-resistant AW90 extruded alloy (Mg-9Al-0.2Y wt %) was developed via alloying and solution-aging treatment (PW = 0.14 mm/y). The solution-treated AW90 alloy exhibits the most severe localized corrosion due to the strong micro-galvanic acceleration effects. The finely dispersed Mg17Al12 phase promotes the strong quasi-passive behavior and uniform corrosion of the aged AW90 alloy due to the formation of a dense and uniform corrosion product film. The high corrosion resistance of the aged AW90 alloy is attributed to the formation of a Mg-Al layered double hydroxide film, which has stronger resistance to chloride ions.

Microstructure evolution and mechanical properties of large-size AZ31 magnesium alloy block fabricated by wire arc additive manufacturing

With the urgent demand for lightweight and integrated structural parts in the aerospace field, the use of cold metal transfer wire arc additive manufacturing (CMT-WAAM) to form large-size magnesium alloy structural parts has become a research hotspot. In this paper, a large AZ31 magnesium alloy multilayer block with a lower porosity was successfully prepared by CMT-WAAM. The AZ31 block exhibits a fully equiaxed grain morphology, the average grain diameters of the top, middle, and bottom are 16.1 µm, 12.4 µm, and 10.4 µm, respectively. The submicron spherical particles measuring 0.09 to 0.4 µm are Mg17Al12 phases, irregular particles are Al8Mn5 + Mg17Al12 composite phases and large particles measuring 5 to 10 µm are Al8Mn5 in AZ31 block. The UTS of CMT-WAAM AZ31 block from the bottom of 239.9 ± 5.0 MPa to the top of 237.3 ± 3.1 MPa, and the EL from the bottom of 22.7 ± 0.6 % to the top of 30.0 ± 1.1 %, exceeding the casting standards. In the CMT-WAAM processed AZ31 alloy, the pre-existing coarse second phase particles in the AZ31 filaments acted as nucleating agents, and the electromagnetic stirring effect in the WAAM process broke up the dendrites and increased the number density of nucleation sites to improve the rate of nucleation, and the complex thermal conditions in the WAAM process restricted the growth of the grains and the precipitated phases. The mechanical properties of AZ31 alloy were improved by effectively refining its grain size and precipitated phase size.

Desensitization of AA5083 alloy via pulsed laser irradiation and its microstructural mechanism

In the present work, a laser surface desensitization (LSD) method was carried out on sensitized AA5083 alloy with the underlying microstructural evolution examined. The enhanced corrosion resistance after LSD process was confirmed by nitric acid mass loss test (NAMLT), immersion test and electrochemical measurements, which is mainly ascribed to the modification of grain boundary chemistry. Accompanied with the dissolution of grain boundary β (Al3Mg2) phase during LSD process, the grain boundaries could be characterized by Mg segregation or nano-sized Mg-rich clusters, which may also be absent from chemical uniformity depending on grain boundary misorientation.

Strengthening of duplex Mg–9Li–3Al–2Zn–1Sn alloy by solid solution and mixed rolling-induced second phase transition

This work investigated the microstructure and mechanical properties of Mg–9Li–3Al–2Zn–1Sn alloy after solid solution and mixed rolling (hot rolling followed by room-temperature rolling). The research results reveal that after solid solution, AlLi and Mg2LiZn3 phases disappear, while MgLi2Al phases partially disappear. The hardness of the β-Li phase is much higher than that α-Mg phase, and the strength of the alloy is significantly increased while the elongation decreases to 1.4 %. Low plasticity is mainly due to lattice distortion and the presence of coarse Sn-rich phases. After mixed rolling, a large quantity of second phase precipitation in the alloy plays a role of second phase strengthening. The Mg17Al12 phases are observed to precipitate inside the α-Mg phase, and the AlLi phases containing MgLi2Al and Mg2LiZn3 nanophases inside are found at the β-Li phase and α-Mg/β-Li phase interface. The YS and UTS of the mixed rolled alloy reach 253 MPa and 273 MPa, respectively, with an improved EL of 18.4 %.

Effect on microstructure and mechanical properties of friction stir welded 5A06 aluminum alloy joints by deep cryogenic treatment

In order to improve the comprehensive mechanical properties of the welded joints of the 5A06 aluminum alloy, friction stir welded (FSW) joints were subjected to deep cryogenic treatment (DCT). The microstructure and mechanical properties were characterised using metallographic microscopy, x-ray diffractometer (XRD), energy spectrometer, microhardness tests, and tensile tests. The experimental results show that DCT refines the structure significantly due to the large temperature difference. This refinement results from an increase in Mg atoms within the α-Al solid solution through the precipitation of Al atoms, forming the Al3Mg2 phase. This enhancement in plasticity is achieved through dispersion distribution. Moreover, as the treatment time of DCT increases, the mechanical properties of the welded joint also improve significantly. The microhardness of the welding joint peaked at DCT3h, rising from 78.8 HV at DCT0h to 87.2 HV at DCT3h. Meanwhile, the tensile strength of the joint reached its maximum at DCT12h, rising from 358.7 MPa at DC0h to 385.3 MPa at DCT12h, representing a 7.4% increase. These experimental results underscore the significant impact of DCT on improving the welded joints.

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.