Mg17Al12 Phase Research Articles

Microstructure, mechanical properties and corrosion resistance of friction stir welded joint of Al–Mg–Mn–Zr–Er alloy

Abstract The microstructure, mechanical properties and corrosion resistance of friction stir welded joint of Al–Mg–Mn–Zr–Er alloy were investigated under three FSW parameter sets: 800 rpm × 100 mm min−1, 800 rpm × 80 mm min−1 and 600 rpm × 80 mm min−1. The microstructural transformation sequence of welded joint is discontinuous dynamic recrystallization, dislocation introduction, dynamic recovery and continuous dynamic recrystallization. The mechanical properties of welded joint are highly correlated with the welding process parameters. The welded joint can obtain good tensile strength and elongation under the parameters of 800 rpm × 100 mm min−1. Corrosion resistance of welded joints has little correlation with welding parameters, but is mainly related to different positions of welded joints. The main influencing factor is grain structure state. The intergranular corrosion susceptibility is related to β(Al3Mg2) phase.

Microstructure, Interface and Strengthening Mechanism of Ni-CNTs/AZ91 Magnesium Matrix Composites.

Ni-CNTs/AZ91 magnesium matrix composites were fabricated by ultrasound treatment combined with a semi-solid stirred method for the first time. The agglomerated spherical Ni-CNTs transferred from spherical shape to clear tubular shape after pre-dispersion treatment. For the Ni-CNTs/AZ91 magnesium matrix composite prepared by semi-solid stirring followed by ultrasonic treatment, Ni-CNTs were evenly distributed in the magnesium matrix or wrapped on the β (Mg17Al12) phase. Mg2Ni were formed at the interface of the magnesium matrix and CNTs by in-situ reaction, which significantly improved the interface bonding strength of CNTs and the Mg matrix. The tensile strength and elongation of 1.0wt.% Ni-CNTs/AZ91 magnesium matrix composites were improved by 36% and 86%, respectively, compared with those of AZ91 matrix alloy. After Ni-CNTs were added to AZ91 matrix alloy, more dimples were observed at the fracture surface. The fracture behavior of Ni-CNTs/AZ91 composite was transformed from a cleavage fracture of AZ91 matrix alloy to a quasi-cleavage fracture. Meanwhile, the CNTs dispersed near the fracture showed a "pull-out" state, which would effectively bear and transfer loads. The strengthening mechanism of CNTs was also discussed.

Enhancing the anti-corrosion performance and biocompatibility of AZ91D Mg alloy by applying roughness pretreatment and coating with in-situ Mg(OH)2/Mg-Al LDH

Corrosion-resistant and biocompatible films were fabricated on AZ91D Mg alloy substrates by varying their roughness levels using metallographic preparation and subsequent hydrothermal procedures. The coated films comprised a mixed structure of Mg(OH)2 and Mg-Al layered double hydroxides (LDH) and exhibited excellent compactness. Coating film thickness increased with decreasing surface roughness. Corrosion resistance was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy. Metallographic pretreatment influenced the chemical activity of the Mg alloy surface and helped modulate the dissolution rate of the Mg17Al12 phase during the hydrothermal procedure. With decreasing roughness of the Mg substrate, the Al3+ concentration gradually increased, accelerating the in-situ formation of the Mg(OH)2/LDH composite coating and improving its crystallinity. A thick and dense Mg(OH)2/LDH coating was synthesized on the Mg substrate with the least roughness, substantially improving the corrosion resistance of the AZ91D alloy. The lowest corrosion current density ((5.73 ± 2.75) × 10−8 A·cm−2) was achieved, which was approximately three orders of magnitude less than that of bare AZ91D. Moreover, the coating demonstrated biocompatibility with no evident cytotoxicity, cellular damage, and hemolytic phenomena. This study provides an effective method for preparing coatings on Mg alloy surfaces with excellent corrosion resistance and biocompatibility.

Microstructure and properties of MgAlCd filler metal scraped brazing AZ31 magnesium alloy joint

In order to simplify the brazing process of magnesium alloy and make the liquid filler metal rapidly wet the base metal, the phase diagram method was used to design the series of Cd22.8Mg9.2Al and Cd26.3Mg15.3Al series filler metal. The brazing of AZ31 magnesium alloy was realized by scraping brazing under the condition of flame heating. The microstructure and phase of the filler metal and brazing seam were analyzed by XRD, SEM, and EDS. The results show that the microstructure of filler metal is composed of CdMg matrix, granular Al12Mg17, and massive (Al) solid solution. The amount of Al12Mg17 and (Al) solid solutions in filler metal increases with the increase of Al content, and the hardness of filler metal also increases. The Al content increases from 9.2 to 15.3%, and Vickers hardness increases from 183.6HV to 252HV. DSC results show that the melting point of filler metal is between 396.1 °C and 401.5 °C. The analysis results of the brazing seam show that the microstructure of the brazing seam is composed of CdMg3 and Al12Mg17. With the increase of Al content in filler metal, the fracture morphology changes from a river like pattern to rock sugar shape, the fracture mode changes from trans-granular fracture to intergranular fracture and the shear strength of joint decreases from 71 MPa to 53 MPa. The main reason for this phenomenon is the increase in the amount and size of the Al12Mg17 phase.

Laser-Arc Hybrid Cladding of Al-Mg Alloy Coating on AZ80 Mg Alloy: Effect of Laser Beam Oscillations Amplitude.

The effect of beam oscillating amplitude on the microstructure and performance of AZ80 Mg alloy cladded with Al-Mg alloy coating by laser–arc hybrid welding was studied. The penetration depth decreases significantly while welds are widened because of the increase in the oscillating area of a laser beam. Alloy segregation and keyhole-induced porosity can be suppressed by the laser beam oscillation. With the increase in the oscillating amplitude, the Al distribution becomes uniform in the weld seam because of the rapid and fierce stirring by the oscillating laser. However, the diluting of the cladded Al alloy restrains the formation of the brittle Mg17Al12 phase, and then causes the weakening of hardness and wear resistance of the cladded layer. Considered comprehensively, the optimized oscillating amplitude was 1 mm, which can produce the weld seam with good appearance, fewer segregation and porosity defects, and acceptable hardness and wear resistance.

(Digital Presentation) Spark Plasma Sintering Fabrication of α/β Interface in Mg Alloys and Analysis of Corrosion Behavior

In Mg alloys, corrosion behavior is known to be related to the microstructure. For example, AZ91D alloy contains an α matrix phase (Mg solid solution), β phases (Mg17Al12) and lamellar α+β microstructures. During the real-time in situ observation of the corrosion process under galvanostatic polarization, filiform corrosion proceeded along the outside of the β-phase (in lamellar α + β microstructure and along the α-mother phase[1]. However, the detailed mechanism of the initiation and growth of filiform corrosion is still unknown. An electrode area contains simplified α + β structure is needed to clarify the corrosion mechanism of Mg alloys. The fabrication of such specimen could be actualized by Spark Plasma Sintering (SPS).The advantage of SPS is that it can produce specimens with high efficiency and few pores. The energy from the pulsed current, self-heating of the workpiece, and particle-to-particle discharge are the combined driving force for sintering. In recent years, many experiments have been reported on the fabrication and strength evaluation of pure Mg and Mg alloys. However, only a few studies have been conducted on the fabrication and corrosion resistance of different phases.In this study, we attempted to fabricate the interface of β and α phases by SPS using pure Al powder and pure Mg powder and other materials. The characterization of different phases was carried out by XRD, EPMA and TEM. The corrosion behavior of the sintered specimens was then observed using an in-situ observation system during open circuit potential measurements. After measurements, the specimen surface was assessed using OM, AES, and FE-SEM.When a 0.25 mm thick Mg sheet was surrounded by pure Al powder, the temperature was set at 420 °C and kept for 30 minutes, a uniform white microstructure was found to form around the Mg sheet. The thickness is about 50 µm. EDS maps and point analysis show that this phase consists a β-phase (Mg17Al12) on the Mg sheet side and Mg23Al30 on the Al powder side. The thickness of the β-phase did not change obviously when the sintering time was extended to 1 hour. Finally, a β phase with a thickness of about 100 μm could be fabricated by using a specimen assembly method of outer Al powder, intermediate layer Mg powder. Analysis of corrosion behavior was done with this specimen. Z. Shao, M. Nishimoto, I. Muto, and Y. Sugawara, Corrosion Science, 192, 109834 (2021).

Mg/MgH2 hydrogen storage system destabilized by recyclable AlH3–NaBH4 composite

While borohydrides, such as NaBH4, were often used as supplements to improve hydrogen storage properties of Mg/MgH2 systems, they have long suffered from high decomposition temperature and irreversible dehydrogenation process. Here, we report that NaBH4 can reversibly serve as a hydrogen storage host and reactant for Mg/MgH2 systems under mild reaction conditions with the help of Al/AlH3. 90 wt%MgH2–5 wt.%AlH3–5 wt.%NaBH4 (M-5AB) has been successfully synthesized using the conventional mechanical alloying technique. The dehydrogenation activation energy and enthalpy are 20% and 9% reduced than those of pure Mg/MgH2. After 10 hydrogen absorption and desorption cycles, the hydrogen storage capacity of M-5AB can reach 6.35 wt%. The X-ray diffraction (XRD) and the transmission electron microscope (TEM) measurements revealed that the interface of additives and Mg/MgH2 decompose to Mg17Al12, MgAlB4 and NaH phases. The Mg17Al12 and MgAlB4 phases reduces the barrier of free energies of hydrogenated and dehydrogenated states, helping NaBH4 to recover after rehydrogenation. These discoveries indicate that Al species can boost the decomposition and reformation of NaBH4, providing a wider degree of freedom for the material design of Mg-based hydrogen storage materials.

Precipitation phase diffusion kinetics of AZ61 alloy under electrical pulse treatment

In this work, electrical pulse treatment and isothermal heat treatment are employed to tailor the microstructure of the hot-rolled AZ61 alloy. The influence of pulsed current on the crystal growth mechanism and precipitation phase diffusion was investigated. According to the findings, electrical pulses enhance the recrystallization and dissolution of Mg17Al12 precipitate in hot-rolled AZ61 alloy. The recrystallization fraction of EPTed samples is higher than that of the isothermal HTed counterparts. The amount of Mg17Al12 phase is considerably reduced with the increased EPT duration. In contrast, the Mg17Al12 phase fraction in isothermal HTed samples is just slightly changed. The Nernst–Einstein formula indicates that the electrical pulse effectively improves the total diffusion flux in the diffusion system via the coupling of athermal effect and thermal effect.

Influence of Ti-6Al-4V particles on the interfacial microstructure and strength-ductility synergetic mechanism of AZ91 magnesium alloy

Although magnesium (Mg) matrix composites have been intensively investigated as promising light structural materials, their relatively low ductile nature limits their wide-scale applications. In this study, Mg-9Al-1Zn (AZ91) Mg matrix composites reinforced by Ti-6Al-4V (TC4) particles were prepared via powder metallurgy. Microstructure observation showed that the interfacial zone is composed of Mg17Al12 and Al-rich phase. The tensile tests suggested that the yield strength, ultimate tensile strength, and elongation display peak values (211 MPa, 303 MPa, 18.7%, respectively) when the content of TC4 particles is 5 wt%. The improvement of mechanical properties can be attributed to the strong interfacial bonding between the Mg matrix and TC4 particles through the formation of coherent interfacial bonding of Al3Ti/Mg21(Zn, Al)17 and semi-coherent interfacial bonding of Mg21(Zn, Al)17/Mg. The strain distribution during the tensile test of the composite was investigated by using digital image correlation technology. The introduction of TC4 reinforcement can relieve the stress concentration and the composites achieve comprehensive mechanical properties with high strength and high plasticity. TC4 particles can improve the matrix strengthening effect by increasing the work hardening capacity. The elongation of the composite increases during tensile loading.

Influence of Soft Phase and Carbon Nanotube Content on the Properties of Hierarchical AZ61 Matrix Composite with Isolated Soft Phase.

Carbon nanotube-reinforced magnesium matrix (CNTs/Mg) composite has great application potential in the transportation industry, but the trade-off between strength and ductility inhibits its widespread application. In order to balance the strength and plasticity of the composite, in this work, on the basis of the AZ61 matrix composite homogeneously reinforced by Ni-coated CNTs (hard phase), 30 vol.% large-size AZ61 particles are introduced as an isolated soft phase to fabricate hierarchical CNTs/AZ61 composites. The compression tests show the fracture strain and compressive strength of this composite increases by 54% and 8%, respectively, compared with homogeneous CNTs/AZ61 composite. During deformation, the hard phase is mainly responsible for bearing the load and bringing high strength, due to the precipitation of the Mg17Al12 phase, uniformly dispersed CNT and strong interfacial bonding of the CNTs/Mg interface through nickel plating and interfacial chemical reaction. Furthermore, the toughening of the soft phase results in high ductility. With the increase in CNT content, the compressive strength of composites is nearly unchanged but the fracture strain gradually decreases due to the stress concentration of CNT and its agglomeration.

Formation of the intermetallic phases Al12Mg17 and Al3Mg2 during heating of elemental Al-Mg composites studied by high-energy X-ray diffraction

The purpose of the present study is to track the formation of the intermetallic phases that form in the binary Al-Mg system and investigate their orientation relationships to the parent Al and Mg elements. Therefore, two compositions Al60Mg40 and Al40Mg60 (wt%), which are very suitable for studying the diffusion of Al in Mg and Mg in Al were heated from room temperature up to elevated temperatures below the melting point. Powder metallurgy, including cold extrusion was used to create a large interface between the Al and Mg, which facilitates fast reaction kinetics. In order to observe the phase formation during heating and analyze the crystal structures, X-ray diffraction using synchrotron radiation was used. The use of high energy X-ray was extremely helpful, enabling the detection of small phase fractions and information on the orientation relationships between the Al and Mg and the intermetallic phases that formed. The γ-Al12Mg17phase was the first phase formed in both alloy compositions on annealing. Subsequently, the β-Al3Mg2phase was formed. After annealing at 400 ºC for 2 h, the Al40Mg60 composition consisted of a very high amount of Al12Mg17 and a small amount of Mg phase while the Al60Mg40 composition consisted of mainly Al3Mg2 and a small fraction of Al12Mg17, indicating that thermodynamic equilibrium has been approximated. On further annealing at 400 ºC for 12 h, both compositions formed only one phase, namely the Al12Mg17 phase in the Al40Mg60 composition and the Al3Mg2 phase in the Al60Mg40 composition. In this condition, a Pitsch-Schrader orientation relationship was found between the Mg and the γ-Al12Mg17 phase, the occurrence of which is discussed within the framework of literature models. No orientation relationship between either the Al or the Mg with the Al3Mg2 phase was found.

Improving mechanical properties of a cast Al–Mg alloy with high Mg content by rapid solidification

Cast Al–Mg alloys with high Mg contents (>10 wt%) have received particular attention due to much lower density than those of other cast Al alloys. However, high amounts of coarse dendritic Al–Mg intermetallic phases substantially deteriorate both strength and ductility. This work aims to reduce amount and size of Al–Mg intermetallic phases by rapid solidification (RS) and to improve both strength and ductility in a cast Al-15 wt%Mg alloy. This paper reports a study on Al-15 wt%Mg alloy processed by a RS technique, namely twin-roll casting (TRC). The results of optical microscopy, electron backscatter diffraction and scanning electron microscopy analysis show refined Al grains and refined granular Al3Mg2 particles, and the results of X-ray diffraction analysis reveal the increased Mg solid solubility and correspondingly the decreased amount of Al3Mg2 phase, in the TRC Al-15 wt% alloy, as compared to the conventionally mold cast (CMC) counterpart. Consequently, the tensile testing results show 0.2% offset yield strength of 243 MPa and ultimate tensile strength of 355 MPa, accompanied by uniform elongation of 3.6%, in the TRC Al-15 wt% alloy, relative to premature fracture in the CMC counterpart. The microstructural features and the mechanisms underlying improved strength and ductility in the TRC Al-15 wt%Mg are analyzed and discussed.

Mechanical and stress corrosion cracking behavior of welded 5059H116 alloy

5059H116 alloy is welded by friction stir welding (FSW) and gas metal arc welding (GMAW). Both welded specimens exhibited inferior strength and percent elongation as compared to base alloy. Soundness of the weld, passivating tendency of finer grains, and depletion of dissolved magnesium from the nugget zone due to discontinuous precipitation of Al3Mg2 phase at the Al6Mn/matrix interface contributed to the superior corrosion resistance of FSW alloy. Slow strain rate tests showed shorter time to failure for GMAW sample, which is attributed to the formation of microcells from chemical heterogeneities and iron-containing second phase dispersoids, and presence of micro-porosity. Data availability statementThe raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations.

Correlation between Microstructures and Tensile Properties in Friction Stir Welding Joint of Zn-Modified 5083 Al Alloy

Various Zn contents were utilized as an alloy element adding in the AA5083 aluminum alloys to optimize the properties. The subsequent characterizing techniques show that the hardness distribution of the friction stir welding (FSW) joint is ‘W’ shaped with the nugget zone relatively high, and the hardness of the thermo-mechanical affected zone (TMAZ) being the lowest. The joint with rotation speed of 600 rpm has the best mechanical properties and no welding defects appear. The grain deformation of the TMAZ is greater under the action of the welding tool and grain growth occurs in the heat affected zone (HAZ). Based on slow strain rate testing (SSRT), the FSW joint of the AA5083 alloy containing Zn 0.50 wt.% showed the highest resistance to stress corrosion cracking (SCC), which is probably due to the formation of Zn phase in place of the β (Al3Mg2) phase during welding.

AZ Serisi Döküm Magnezyum Alaşımlarının Termal Özellikleri

Bu çalışmada, AZ serisi döküm magnezyum alaşımlarının ısıl davranışları (ısıl yayılma ve ısıl iletkenlik) üzerine deneysel bir araştırma sunmaktadır. Deneyde kullanılan alaşım bileşenlerinden Al’nin değişimi (ağırlıkça % 1-9 arasında) alaşımların ısıl yayılma ve ısıl iletkenliklerini nasıl etkilediğini, yoğunluk ve sertlik üzerindeki değişimler incelenmiştir. Alaşımların mikroyapı değişimlerinin ve mikroyapıda görülen intermetalik fazın (Mg17Al12) alaşımların ısıl yayınım, ısıl iletkenlik, yoğunluk ve sertlik üzerine etkisi olduğu görülmüştür. Alaşımın ısıl özellikleri, alaşımdaki Al içeriğine bağlı olarak değişmiştir. Alaşımların termal özellikleri sıcaklık artışına bağlı olarak (sıcaklık değişimi 25 °C- 400 °C arası) artmıştır. En yüksek termal yayılma AZ61 alaşımında gözlenmiştir.

Effect of Zn and Cu Addition on Microstructure and Mechanical Properties of Al-10wt%Mg Alloy

5xxx series aluminum alloys have been widely used in automobiles, ships, aerospace and other fields for their low density, good corrosion resistance and weldability. The present study designs a new Al-10.0Mg-1.0Zn-0.15Cu (wt%) alloy with different composition from the traditional 5xxx series and 7xxx series aluminum alloys; the Zn/Mg ratio is below 1.0. Detailed characterization by scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) has been carried out to reveal the microstructural evolution. The results show that the addition of Zn and Cu inhibits the precipitation of the Al3Mg2 phase in the traditional Al-Mg binary alloy during annealing and promotes the precipitation of T-Mg32(Al,Zn)49 phase, which contributes to precipitation strengthening. After 75% rolling and 150 °C annealing, the T-Mg32(Al,Zn)49 phase precipitates and the alloy obtains good strength and plasticity coordination with 0.2% offset yield strength of 519 MPa and ultimate tensile strength of 653 MPa, accompanied by uniform elongation of 8.1%. The mechanisms underlying the improved strength and plasticity in the Al-10.0Mg-1.0Zn-0.15Cu (wt%) alloy are discussed.

Adsorption and decomposition of ZDDP on lightweight metallic substrates: Ab initio and experimental insights

Lightweight alloys substitute steel in a wide range of industrial applications. It is still unclear whether the lubricant additives currently employed to reduce friction of sliding metallic parts are also efficient on non-ferrous substrates. In particular, the functionality of zinc dialkyldithiophosphates (ZDDPs) in contact with Al- and Mg-containing alloys still needs to be understood. In this work, we describe the properties of ZDDP at Al(111), Al(001), Al(331), Mg(0001) and Mg17Al12 surfaces and interfaces. Our calculations indicate that molecular fragments originated from ZDDP chemisorb more strongly on the intermetallic phase Mg17Al12 with respect to aluminum and magnesium, due to the higher surface energy of the mixed substrate. Ab initio molecular dynamics simulations show that the kinetics of the additive decomposition is significantly different on Al and the mixed phase. These results are supported by atomic force microscopy sliding tests, which revealed that the tribofilm formation is observed only on the latter substrate. This work suggests that the tribological performance of lightweight alloys can be enhanced by increasing the additive-surface chemical interactions.

Investigation on microstructure, mechanical properties and fracture mechanism of Mg/Al laminated composites

Herein, the Al/Mg laminated composites were successfully prepared by powder metallurgy-roll bonding, and the effect of annealing time on the microstructure and mechanical properties was studied, and the tensile and shear fracture mechanisms were revealed. The results show that, a diffusion layer with three-layer structure was formed at the Al/Mg interface during the annealing process at 300°C, which were consisted by Mg32Al47Cu7, Al3Mg2 and Al12Mg17 phases. After annealing for 60 min, the ultimate tensile strength and interfacial shear strength of the sample reached the best, with average values of 262.98±6.18 MPa and 27.83±1.59 MPa, respectively. The specimen presented multi-step fracture characteristics during tensile process, i.e., the diffusion layer with hard and brittle interface cracked locally first, and then the Mg matrix fractured, and finally the Al matrix fractured. During the shear test, the fracture position was between Al3Mg2 phase layer and Mg32Al47Cu7 phase layer, which was characterized by brittle cleavage fracture.

The second phases of Mg–xAl–ySi–Ca alloys and their influences on properties

The types and changes of the second phases in the Mg–xAl–ySi–0.3Ca alloys and their effects on the properties of the alloys were studied. The results showed that within a certain range of Si and Al content, Si had the greatest influence on the size of the Mg2Si phase, while Al content affected the size and morphology of Mg17Al12 and Mg2Si phases. The CaMgSi phases were less affected by the Al and Si content. In a tensile test, the as-cast alloy had the best performance when it contained small Mg17Al12 and Mg2Si phases, and the Mg17Al12 phase was more likely to become the fracture source. The alloy we tested with the best corrosion resistance was Mg–4Al–0.7Si–0.3Ca alloy, the worst was Mg–6Al–0.7Si–0.3Ca alloy.

Effects of intermetallic phases on electrochemical properties of powder metallurgy Mg-6%Al-5%Pb anode alloy used for seawater activated battery

The changes in intermetallic phases of Mg-6%Al-5%Pb (Mg-Al-Pb) alloy prepared by powder metallurgy and their effects on electrochemical properties were studied. Experimental results showed that coarse Mg17Al12 phases (with size ranges from 20 μm to 70 μm) and fine Mg2Pb phases (with the size of 100 nm scale) formed in the mixed Al, Pb and Mg powder during the hot press sintering procedure. Fine Mg2Pb phases exhibit strong diffusional ability to diffuse into Mg17Al12 phases. Extruding further promotes the diffusion of Mg2Pb phases into Mg17Al12 phases. Solution treatment produced a mixed microstructure which is Mg17Al12 phase containing Mg2Pb phases inside and made other Mg2Pb phases homogeneously distributed in Mg matrix. Mg17Al12 phases and the gathered Mg2Pb phases will accumulate the Mg(OH)2 corrosion products, which impedes the subsequent discharge behavior. Homogeneously distributed Mg2Pb phases will fall off during discharge, which makes the discharge curve more stable. The mixed microstructure has positive effect on corrosion resistance and discharge potential. Therefore, solution-treated alloy shows the highest negative potential and the smoothest curve during the galvanostatic discharge test. Compared with the commercial AZ61 sheet, solution-treated alloy exhibit much higher anode properties in Mg/PbCl2 battery test. Thus, the solution-treated alloy could serve as an excellent anode in seawater-activated batteries.