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1.
In this study, wetting has been characterized by measuring the contact angles of AZ92 Mg alloy on Ni-electroplated steel as a function of temperature. Reactions between molten Mg and Ni led to a contact angle of about 86 deg in the temperature range of 891 K to 1023 K (618 °C to 750 °C) (denoted as Mode I) and a dramatic decrease to about 46 deg in the temperature range of 1097 K to 1293 K (824 °C to 1020 °C) (denoted as Mode II). Scanning and transmission electron microscopy (SEM and TEM) indicated that AlNi + Mg2Ni reaction products were produced between Mg and steel (Mg-AlNi-Mg2Ni-Ni-Fe) in Mode I, and just AlNi between Mg and steel (Mg-AlNi-Fe) in Mode II. From high resolution TEM analysis, the measured interplanar mismatches for different formed interfaces in Modes I and II were \( 17{\kern 1pt} \;{\text{pct}}_{{\{ 10\overline 11\}_{\text{Mg}} //\{ 110\}_{\text{AlNi}} }} \)-\( 104.3\;{\text{pct}}_{{\{ 110\}_{\text{AlNi}} //\left\{ {10\overline{1}0} \right\}_{{{\text{Mg}}_{ 2} {\text{Ni}}}} }} \)-\( 114\,{\text{pct}}_{{\left\{ {0003} \right\}_{{{\text{Mg}}_{ 2} {\text{Ni}}}} //\{ 111\}_{\text{Ni}} }} \) and \( 18\,{\text{pct}}_{{\{ 10\overline 11\}_{\text{Mg}} //\{ 110\}_{\text{AlNi}} }} \)-\( 5\,{\text{pct}}_{{\left\{ {110} \right\}_{\text{AlNi}} //\{ 110\}_{\text{Fe}} }} \), respectively. An edge-to-edge crystallographic model analysis confirmed that Mg2Ni produced larger lattice mismatching between interfaces with calculated minimum interplanar mismatches of \( 16.4\,{\text{pct}}_{{{\text{\{ 10}}\overline 1 1 {\text{\} }}_{\text{Mg}} / / {\text{\{ 110\} }}_{\text{AlNi}} }} \)-\( 108.3\,{\text{pct}}_{{{\text{\{ 110\} }}_{\text{AlNi}} / / {\text{\{ 10}}\overline 1 1 {\text{\} }}_{{{\text{Mg}}_{ 2} {\text{Ni}}}} }} \)-\( 17.2\,{\text{pct}}_{{{\text{\{ 10}}\overline 1 1 {\text{\} }}_{{{\text{Mg}}_{ 2} {\text{Ni}}}} / / {\text{\{ 100\} }}_{\text{Ni}} }} \) for Mode I and \( 16.4\,{\text{pct}}_{{{\text{\{ 10}}\overline1 1 {\text{\} }}_{\text{Mg}} / / {\text{\{ 110\} }}_{\text{AlNi}} }} \)-\( 0.6\,{\text{pct}}_{{{\text{\{ 111\} }}_{\text{AlNi}} / / {\text{\{ 111\} }}_{\text{Fe}} }} \) for Mode II. Therefore, it is suggested that the poor wettability in Mode I was caused by the existence of Mg2Ni since AlNi was the immediate layer contacting molten Mg in both Modes I and II, and the presence of Mg2Ni increases the interfacial strain energy of the system. This study has clearly demonstrated that the lattice mismatching at the interfaces between reaction product(s) and substrate, which are not in direct contact with the liquid, can greatly influence the wetting of the liquid.  相似文献   

2.
In the present study, microstructural and mechanical properties of diffusion bonding of AZ31–Mg with Al 5754, Al 6061, and Al 7039 alloys were compared under same conditions. The vacuum diffusion processes were performed at a temperature of 440 °C, the pressure of 29 MPa, and a vacuum of 1?×?10?4 torr for 60 min. The microstructural characterizations were investigated using optical microscopy and scanning electron microscopy equipped with EDS analysis and linear scanner. The XRD analysis was performed to study phase figures near the interface zone. The results revealed the formation of brittle intermetallic compounds like Al12Mg17, Al3Mg2, and their other combinations at bonding interfaces of all samples. Additionally, the hardness of Al alloys seemed to play a key role in increasing diffusion rate of magnesium atoms toward the aluminum atoms, with Al 6061 alloy having the highest diffusion rate. It consequently led to an increase in diffusion rate and thus formation of a strong diffusion bonding between magnesium and aluminum alloys. The highest strength was about 42 MPa for the diffusion bonding between Mg AZ31 and Al 6061. Further investigations on surfaces indicated that the brittle phases especially Al3Mg2 caused brittle fracturing.  相似文献   

3.
Sound joints between an AA6016 aluminum sheet of 1.2-mm thickness and a low-carbon galvanized steel sheet of 0.77-mm thickness are obtained using the laser pseudo-brazing method. A zinc-based aluminum alloy is used as a filler wire with optimized process parameters for laser pseudo-brazing. Metallurgical investigation of the joint is carried out using a scanning electron microscope and energy-dispersive X-ray analysis. Joints produced using Al-Zn filler wire showed a moderate strength and quality with a layer containing principally Fe2Al5Zn x type intermetallics of ~10-μm thickness. Failure in the heat-affected zone of aluminum is found to be dominative, while in some cases, fracture along the interface between the intermetallic layer and the steel sheet is observed.  相似文献   

4.
Low melting point Zr-based filler metals with melting point depressants (MPDs) such as Cu and Ni elements are used for titanium brazing. However, the phase transition of the filler metals in the titanium joint needs to be explained, since the main element of Zr in the filler metals differs from that of the parent titanium alloys. In addition, since the MPDs easily form brittle intermetallics, that deteriorate joint properties, the phase evolution they cause needs to be studied. Zr-based filler metals having Cu content from 0 to 12 at. pct and Ni content from 12 to 24 at. pct with a melting temperature range of 1062 K to 1082 K (789 °C to 809 °C) were wetting-tested on a titanium plate to investigate the phase transformation and evolution at the interface between the titanium plate and the filler metals. In the interface, the alloys system with Zr, Zr2Ni, and (Ti,Zr)2Ni phases was easily changed to a Ti-based alloy system with Ti, Ti2Ni, and (Ti,Zr)2Ni phases, by the local melting of parent titanium. The dissolution depths of the parent metal were increased with increasing Ni content in the filler metals because Ni has a faster diffusion rate than Cu. Instead, slow diffusion of Cu into titanium substrate leads to the accumulation of Cu at the molten zone of the interface, which could form undesirable Ti x Cu y intermetallics. This study confirmed that Zr-based filler metals are compatible with the parent titanium metal with the minimum content of MPDs.  相似文献   

5.
Joints of zinc coated steel (DX54D+Z200) to aluminium alloys (AW6181‐T4 and AW5182‐H111) were produced by the Cold Metal Transfer (CMT) technique, a modified metal inert gas (MIG) joining process. The aluminium alloy sheets and the AISi3Mn1 filler material are welded, while brazing occurs between the AISi3Mn1 filler and the steel sheet. At the interface between the Al‐based filler and the steel sheet, aluminium‐rich intermetallic FexAly‐phases are formed. The comparatively low heat input of the CMT process and the choice of filler composition limit the thickness of the intermetallic phase seam (IMP) to a few micrometers. The structure of the intermetallic phase and its morphology are strongly influenced by the alloying elements (Mn, Si) of the filler. Tensile tests and crash tests of the steel to aluminium alloy joints revealed good mechanical properties.  相似文献   

6.
Microstructural evolution and interfacial reactions during active metal vacuum brazing of Ti (grade-2) and stainless steel (SS 304L) using a Ag-based alloy containing Cu, Ti, and Al was investigated. A Ni-depleted solid solution layer and a discontinuous layer of (Ni,Fe)2TiAl intermetallic compound formed on the SS surface and adjacent to the SS-braze alloy interface, respectively. Three parallel contiguous layers of intermetallic compounds, CuTi, AgTi, and (Ag,Cu)Ti2, formed at the Ti-braze alloy interface. The diffusion path for the reaction at this interface was established. Transmission electron microscopy revealed formation of nanocrystals of Ag-Cu alloy of size ranging between 20 and 30 nm in the unreacted braze alloy layer. The interdiffusion zone of β-Ti(Ag,Cu) solid solution, formed on the Ti side of the joint, showed eutectoid decomposition to lamellar colonies of α-Ti and internally twinned (Cu,Ag)Ti2 intermetallic phase, with an orientation relationship between the two. Bend tests indicated that the failure in the joints occurred by formation and propagation of the crack mostly along the Ti-braze alloy interface, through the (Ag,Cu)Ti2 phase layer.  相似文献   

7.
Lap joints of aluminum alloy A6061-T6 and AZ31B magnesium alloy were produced by cold metal transfer welding with Al-5 %Si filler metal. Four heat inputs designated as A (175 J/mm), B (185 J/mm), C (195 J/mm) and D (205 J/mm) were used during the process and the joints made were subjected to analysis of microstructure, mechanical properties and corrosion behaviour. The thickness of the fusion line (diffusion layer) varied from 3 to 12 µm depending on the heat input. It was also found that the joints made using the heat input of 205 J/mm exhibited highest tensile strength of 360 N/mm, least tensile stress in the weld and better pitting corrosion resistance. Electron microscopy study of the weld revealed the presence of β′-Mg2Si, Al6Mn and β-Al3Mg2 particles. X-ray diffraction study in the weld revealed the formation of γ-Al12Mg17 and β-Al3Mg2 phase with Mg2Si strengthening precipitates. Tensile failure occurred at the fusion line near magnesium.  相似文献   

8.
Development of a low-melting-point filler metal for brazing aluminum alloys   总被引:5,自引:0,他引:5  
The study is concerned with developing low-melting-point filler metals for brazing aluminum alloys. For this purpose, thermal analyses of a series of Al-Si-Cu-Sn filler metals have been conducted and corresponding microstructures observed. The results showed that the liquidus temperature of Al-Si-Cu filler metals dropped from 593 °C to 534 °C, when the amount of copper was increased from 0 to 30 pct. As the copper content reached further to 40 pct, the liquidus temperature would rise to 572 °C. By adding 2 pct tin into the Al-Si-20Cu alloys, the liquidus and solidus temperature would fall from 543 °C to 526 °C and from 524 °C to 504 °C, respectively. The main microstructures of Al-Si-Cu alloys consist of the α-Al solid solution, silicon particles, the CuAl2 (ϑ) intermetallic, and the eutectic structures of Al-Si, Al-Cu, and Al-Si-Cu. For further improvement of the brazability of this filler metal, magnesium was added as a wetting agent, which would remove the residual oxygen and moisture from the brazed aluminum surface and reduce the oxide film. Based on results gleaned from the thermal analyses, a new filler metal with the composition Al-7Si-20Cu-2Sn-1Mg is proposed, which possesses a melting temperature range of 501 °C to 522 °C and a microstructure that includes an Al-Si solid solution, silicon particles, a tin-rich phase, and CuAl2, CuMgAl2, and Mg2Si intermetallic compounds. When this filler metal was used to braze the 6061-T6 aluminum alloy, an optimized bonding strength of 196 ± 19 MPa was achieved.  相似文献   

9.
To investigate the influence of Zn coating on the joining of magnesium alloy AZ31?to Zn-coated steel, dissimilar metal joining both with and without Zn coating was performed by the laser welding-brazing (LWB) process. Welding characteristics including joint appearance, identification of interfacial reaction layers, and mechanical properties were comparatively studied. The results indicated that the presence of Zn coating promoted the wetting of liquid filler wire on the steel substrate. Heterogeneous interfacial reaction layers formed along the interface between the Mg alloy and Zn-coated steel, whereas no distinct reaction layer and increased concentration of Al were identified at the interface between the Mg alloy and noncoated steel. The maximum tensile-shear strength of Mg/steel lap joint with Zn coating reached 180?N/mm, which was slightly higher than that achieved without Zn coating (160?N/mm). Failure of joint in both cases occurred at the interface; however, the fracture mode was found to differ. For Zn-coated steel, the crack propagated along the Mg-Zn reaction layer and Fe-Al phase, with little Mg-Zn reaction phases remaining on the steel side. As for noncoated steel, some remnants of the seam adhered to the steel substrate.  相似文献   

10.
The present article focuses on the high-temperature mechanical properties of the magnesium alloy AZ91. The addition of rare-earth (RE) elements up to 2 wt pct improves both yield and tensile strengths at 140 °C by replacing the Mg17Al12 phase with RE-containing intermetallic compounds. This intermetallic phase is thermally and metallurgically stable and is expected to boost the grain-boundary strengthening. It also increases the resistance of grain boundaries to flow at high temperatures. Further increases of RE additions reduce strength and ductility due to growth of the Al11RE3 brittle phase, which has sharp edges. Still, at a 3 wt pct RE addition, the strength of the alloy at high temperatures is more than that of AZ91.  相似文献   

11.
In the current study, solid-state diffusion bonding between Ti-6Al-4V (TiA) and 304 stainless steel (SS) using pure nickel (Ni) of 200-μm thickness as an intermediate material was carried out in vacuum. Uniaxial compressive pressure and temperature were kept at 4 MPa and 1023 K (750 °C), respectively, and the bonding time was varied from 30 to 120 minutes in steps of 15 minutes. Scanning electron microscopy images, in backscattered electron mode, revealed the layerwise Ti-Ni-based intermetallics like either Ni3Ti or both Ni3Ti and NiTi at titanium alloy-nickel (TiA/Ni) interface, whereas nickel-stainless steel (Ni/SS) interface was free from intermetallic phases for all the joints. Chemical composition of the reaction layers was determined by energy dispersive spectroscopy (SEM–EDS) and confirmed by X-ray diffraction study. Maximum tensile strength of ~382 MPa along with ~3.7 pct ductility was observed for the joints processed for 60 minutes. It was found that the extent of diffusion zone at Ni/SS interface was greater than that of TiA/Ni interface. From the microhardness profile, fractured surfaces, and fracture path, it was demonstrated that the failure of the joints was initiated and propagated apparently at TiA/Ni interface near Ni3Ti intermetallic for bonding time less than 90 minutes, and through Ni for bonding time 90 minutes and greater.  相似文献   

12.
An investigation was carried out on the solid-state diffusion bonding between Ti-6Al-4V (TiA) and 304 stainless steel (SS) using pure nickel (Ni) of 200-μm thickness as an intermediate material prepared in vacuum in the temperature range from 973 K to 1073 K (700 °C to 800 °C) in steps of 298 K (25 °C) using uniaxial compressive pressure of 3 MPa and 60 minutes as bonding time. Scanning electron microscopy images, in backscattered electron mode, had revealed existence of layerwise Ti-Ni-based intermetallics such as either Ni3Ti or both Ni3Ti and NiTi at titanium alloy-nickel (TiA/Ni) interface, whereas nickel-stainless steel (Ni/SS) diffusion zone was free from intermetallic phases for all joints processed. Chemical composition of the reaction layers was determined in atomic percentage by energy dispersive spectroscopy and confirmed by X-ray diffraction study. Room-temperature properties of the bonded joints were characterized using microhardness evaluation and tensile testing. The maximum hardness value of ~800 HV was observed at TiA/Ni interface for the bond processed at 1073 K (800 °C). The hardness value at Ni/SS interface for all the bonds was found to be ~330 HV. Maximum tensile strength of ~206 MPa along with ~2.9 pct ductility was obtained for the joint processed at 1023 K (750 °C). It was observed from the activation study that the diffusion rate at TiA/Ni interface is lesser than that at the Ni/SS interface. From microhardness profile, fractured surfaces and fracture path, it was demonstrated that failure of the joints was initiated and propagated apparently at the TiA/Ni interface near Ni3Ti intermetallic phase.  相似文献   

13.
Li  Guangyu  Jiang  Wenming  Guan  Feng  Zhu  Junwen  Yu  Yang  Fan  Zitian 《Metallurgical and Materials Transactions A》2022,53(10):3520-3527

The metallurgical bonding of Mg/Al bimetal by liquid–liquid compound casting was realized via co-deposition Cu–Ni alloy coating. The metallurgical layer of the Mg/Al bimetal consisted of Cu solid solution, Cu2Mg and (Al0.7Cu1.3) Mg, Mg solid solution, Al3Ni2, and Mg2Cu. Vickers hardness of the interface was between 149.9 and 209 HV, which was significantly lower than those of Al–Mg intermetallic compounds. The formation mechanism of the interface was attributed to interdiffusion among AZ91D, A356, and Cu–Ni alloy coating.

  相似文献   

14.
Creep properties of AZ91 magnesium alloy and AZRC91 (AZ91 + 1 wt pct RE + 1.2 wt pct Ca) alloy were investigated using the impression creep method. It was shown that the creep properties of AZ91 alloy are significantly improved by adding Ca and rare earth (RE) elements. The improvement in creep resistance is mainly attributed to the reduction in the amount and continuity of eutectic β(Mg17Al12) phase as well as the formation of new Al11RE3 and Al2Ca intermetallic compounds at interdendritic regions. It was found that the stress exponent of minimum creep rate, n, varies between 5.69 and 6 for AZ91 alloy and varies between 5.81 and 6.46 for AZRC91 alloy. Activation energies of 120.9 ± 8.9 kJ/mol and 100.6 ± 7.1 kJ/mol were obtained for AZ91 and AZRC91 alloys, respectively. It was shown that the lattice and pipe-diffusion-controlled dislocation climb are the dominant creep mechanisms for AZ91 and AZRC91 alloys, respectively. The constitutive equations, correlating the minimum creep rate with temperature and stress, were also developed for both alloys.  相似文献   

15.
Liquid-phase bonding between a Mg alloy (AZ31) and low-carbon steel was attempted at 773 K (500 °C) using Ag as an interlayer that forms a eutectic melt with the Mg alloy at this temperature. On the AZ31 side, eutectic melting and subsequent isothermal solidification were observed, and it was confirmed that the solidification of the eutectic liquid was promoted by the diffusion of Ag into the AZ31 base metal. On the steel side, Al was transported from AZ31 during the eutectic melting and isothermal solidification. This transported Al was enriched at the steel surface and reacted with steel to form a uniform, thin Fe-Al intermetallic compound layer. After the isothermal solidification, strong bonding was achieved via the thin intermetallic compound layer between AZ31 and steel, and no Ag remained at the bonding interface. The strength of the joint was found to be higher than the yield strength of AZ31.  相似文献   

16.
Pure magnesium was recycled from partially oxidized 50.5 wt pct Mg-Al scrap alloy and AZ91 Mg alloy (9 wt pct Al, 1 wt pct Zn). Refining experiments were performed using a eutectic mixture of MgF2-CaF2 molten salt (flux). During the experiments, potentiodynamic scans were performed to determine the electrorefining potentials for magnesium dissolution and magnesium bubble nucleation in the flux. The measured electrorefining potential for magnesium bubble nucleation increased over time as the magnesium content inside the magnesium alloy decreased. Potentiostatic holds and electrochemical impedance spectroscopy were employed to measure the electronic and ionic resistances of the flux. The electronic resistivity of the flux varied inversely with the magnesium solubility. Up to 100 pct of the magnesium was refined from the Mg-Al scrap alloy by dissolving magnesium and its oxide into the flux followed by argon-assisted evaporation of dissolved magnesium and subsequently condensing the magnesium vapor. Solid oxide membrane electrolysis was also employed in the system to enable additional magnesium recovery from magnesium oxide in the partially oxidized Mg-Al scrap. In an experiment employing AZ91 Mg alloy, only the refining step was carried out. The calculated refining yield of magnesium from the AZ91 alloy was near 100 pct.  相似文献   

17.
Compression-bonded Ni-sputtered Al foil multilayers with various atomic ratios of Al/Ni are fabricated with various bilayer thicknesses. The microstructures that are formed after the self-propagating combustion using laser ignition result in equilibrium phases in the Al/Ni binary system. Homogeneous intermetallic compounds for Al3Ni2 and AlNi are obtained for the first time in the micrometer-scale multilayers through controlling the Ni layer thickness. The onset temperatures of the multilayers are below 800 K (527 °C) for all multilayer samples. The maximum temperatures correspond to the liquidus temperatures of the intermetallic compounds. The self-propagating direction is divided into a transverse propagating direction and a gross propagating direction. The measured gross propagation velocities vary widely without exhibiting a clear trend. However, the transverse propagation velocity is dependent on the measured maximum temperatures, while the effects of the bilayer thickness are not discernible. The measured transverse propagation velocities are similar to the reported propagation velocities for sputtered multilayers with similar bilayer thicknesses.  相似文献   

18.
Infrared brazing of Ti-6Al-4V and 17-4 PH stainless steel using the BAg-8 filler metal was performed in this study. A nickel barrier layer 10 μm thick was introduced on the 17-4 PH stainless steel before infrared brazing. For the specimen that was infrared brazed at 800 °C and 850 °C for less than 300 seconds, the Ni layer served as an effective barrier layer to prevent the formation of Ti-Fe intermetallics. Experimental results show that the average shear strength of the joint can be greatly improved for the specimen by Ni plating. Comparing the specimens with and without electroless-plated Ni film, the former has no Ti-Fe intermetallic compound, but interfacial CuNiTi and NiPTi phases are observed in the latter. The fractured location of the joint after the shear test is changed from the interfacial TiFe (without Ni plating) into the TiCu reaction layer (with Ni plating). The plated Ni layer is consumed for the specimen that was infrared brazed at 880 °C for 300 seconds, and its bonding strength is impaired. Consequently, a lower brazing temperature and/or time are still preferred even though a plated Ni barrier layer is applied.  相似文献   

19.
The good specific strength and specific modulus of magnesium alloys had drawn the attention of the automotive manufacturers for use in fuel efficient vehicles. Among the cast magnesium alloys, AZ91 (Mg?C9Al?C1Zn) is the most sought alloy because of its good casting properties. However, this alloy loses its strength and creep resistance properties above 120?°C due to softening of the ?? phase (Mg17Al12). Hence, this alloy cannot be used for making heavier engine components (power train), which require the thermal stability up to about 250?°C. The paper discusses the approach of modifying the AZ91 alloy by minor alloying additions to improve the high temperature withstanding capability without significantly affecting its casting properties. Additions of Ca to AZ91 alloy to the levels of about 0.4?wt% increased the ambient and high temperature strength of the base alloy. Additions of other minor alloying elements such as Sb, Pb, rare earths etc. can also increase the high temperature capability of the AZ91 by further modifying the ?? phase structure. The paper overviews the work carried out by the authors on the role of different alloying additions on the microstructure and mechanical properties of AZ91 magnesium alloys.  相似文献   

20.
Diffusion brazing of Al-6061 alloy containing 15 vol. pct Al2O3 particles was attempted using Cu-Sn interlayer. Joint formation was attributed to the solid-state interdiffusion of Cu and Sn followed by eutectic formation and subsequent isothermal solidification. Examination of the joint region using scanning electron microprobe analyzer (EPMA), wavelength dispersive spectroscopy (WDS) and X-ray diffraction (XRD) showed the formation of intermetallic phases such as Al7Cu3Mg3, Mg2Cu6Al5, Cu3Sn, and Mg2Sn. The results indicated an increase in joint strength with increasing bonding time giving the highest joint shear strength of 94 MPa at a bonding duration of 3 hours.  相似文献   

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