Mg对Zn--11%Al合金镀层凝固组织及合金层生长的影响

将工业纯铁分别在510℃的Zn-11% Al、Zn-11% Al-1.5% Mg、Zn-11% Al-3% Mg和Zn-11% Al-4.5% Mg合金熔池中进行不同时间的热浸镀,使用X射线衍射仪、扫描电子显微镜、能谱仪等仪器设备,研究Mg含量对Zn-11% Al合金镀层凝固组织和镀层中Fe-Al合金层生长的影响.结果表明:Zn-11% Al合金镀层凝固组织由富Al相和Zn/Al二元共晶组成;随着Zn-11% Al-x% Mg合金中Mg含量的增加,合金镀层的凝固组织中逐渐出现Zn/Al/MgZn₂三元共晶、块状MgZn₂相和Al/MgZn₂二元共晶.四种合金镀层中合金层主要由Fe₂Al₅Zn_x和FeAl₃Zn_x相组成,合金层的厚度随浸镀时间的增加而增加,Mg含量的增加使Fe-Al合金层生长速率指数和生长速率降低.在Zn-11% Al合金镀层中Fe-Al合金层形成的初期,可形成致密稳定的Fe-Al化合物层;热浸镀120 s后,扩散通道的移动使Fe-Al化合物层失稳破裂.Zn-11% Al-x% Mg合金中Mg元素可明显推迟液Zn进入镀层中Fe-Al合金层的时间,使Fe-Al合金层更加稳定和致密.      

Design and Achievement of Metallurgical Bonding of Mg/Al Interface Prepared by Liquid–Liquid Compound Casting via a Co-deposited Cu–Ni Alloy Coating

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.

     

A Comprehensive Study of Diffusion Bonding of Mg AZ31 to Al 5754, Al 6061 and Al 7039 Alloys

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.     

Thermochemical Analysis of Phases Formed at the Interface of a Mg alloy-Ni-plated Steel Joint during Laser Brazing

The thermodynamic stability of precipitated phases at the steel-Ni-Mg alloy interface during laser brazing of Ni-plated steel to AZ31B magnesium sheet using AZ92 magnesium alloy filler wire has been evaluated using FactSage thermochemical software. Assuming local chemical equilibrium at the interface, the chemical activity–temperature–composition relationships of intermetallic compounds that might form in the steel-Ni interlayer-AZ92 magnesium alloy system in the temperature range of 873 K to 1373 K (600 °C to 1100 °C) were estimated using the Equilib module of FactSage. The results provided better understanding of the phases that might form at the interface of the dissimilar metal joints during the laser brazing process. The addition of a Ni interlayer between the steel and the Mg brazing alloy was predicted to result in the formation of the AlNi, Mg₂Ni, and Al₃Ni₂ intermetallic compounds at the interface, depending on the local maximum temperature. This was confirmed experimentally by laser brazing of Ni electro-plated steel to AZ31B-H24 magnesium alloy using AZ92 magnesium alloy filler wire. As predicted, the formation of just AlNi and Mg₂Ni from a monotectic and eutectic reaction, respectively, was observed near the interface.     

Microstructure and Interfacial Reactions During Active Metal Brazing of Stainless Steel to Titanium

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.     

Magnesium silicide intermetallic alloys

Methods of induction melting an ultra-low-density magnesium silicide (Mg₂Si) intermetallic and its alloys and the resulting microstructure and microhardness were studied. The highest quality ingots of Mg₂Si alloys were obtained by triple melting in a graphite crucible coated with boron nitride to eliminate reactivity, under overpressure of high-purity argon (1.3 X 10⁵ Pa), at a temperature close to but not exceeding 1105 °C ± 5 °C to avoid excessive evaporation of Mg. After establishing the proper induction-melting conditions, the Mg-Si binary alloys and several Mg₂Si alloys macroalloyed with 1 at. pct of Al, Ni, Co, Cu, Ag, Zn, Mn, Cr, and Fe were induction melted and, after solidification, investigated by optical microscopy and quantitative X-ray energy dispersive spectroscopy (EDS). Both the Mg-rich and Si-rich eutectic in the binary alloys exhibited a small but systematic increase in the Si content as the overall composition of the binary alloy moved closer toward the Mg₂Si line compound. The Vickers microhardness (VHN) of the as-solidified Mg-rich and Si-rich eutectics in the Mg-Si binary alloys decreased with increasing Mg (decreasing Si) content in the eutectic. This behavior persisted even after annealing for 75 hours at 0.89 pct of the respective eutectic temperature. The Mg-rich eutectic in the Mg₂Si + Al, Ni, Co, Cu, Ag, and Zn alloys contained sections exhibiting a different optical contrast and chemical composition than the rest of the eutectic. Some particles dispersed in the Mg₂Si matrix were found in the Mg₂Si + Cr, Mn, and Fe alloys. The EDS results are presented and discussed and compared with the VHN data. Formerly Formerly     

Roll-Bonded Tri-Layered Mg/Al/Stainless Steel Clad Composites and their Deformation and Fracture Behavior

The deformation and fracture behaviors of roll-bonded tri-layered Mg/Al/stainless steel (SST) composite plates were studied. Brittle interfacial reaction compounds were observed at the Mg/Al interface upon annealing at and above 573 K (300 °C), whereas no visible interfacial reaction compounds were observed at Al/SST interfaces even after annealing up to 673 K (400 °C). The strength of the tri-layered Mg/Al/SST clad plates is in close agreement with those calculated from the strength data of the separated Mg, Al, and ST layers using the rule of mixture. The fracture strain components of the tri-layered clad in the absence of brittle interfacial intermetallic layer far exceed those calculated based on the fracture strain data of separated Mg, Al, and SST sheets. The enhanced ductility of the clad composites is due to the suppression of the localized deformation in a metallic layer by other metallic layers caused by the mutual constraint imposed by an adjacent layer. On the other hand, the fracture strain was found to be reduced in the presence of intermetallic layers between the metallic substrates. Cracks perpendicular to the stress axis were observed in the intermetallic compound layer between Mg and Al, inducing the localized slip in the vicinity of intermetallic cracks and premature fracture of the Mg alloy layer.     

Effect of Au Addition on the Microstructure and Properties of Ag-4Pd Bonding Wires

Silver-based bonding wires such as Ag-4Pd and Ag-8Au-3Pd have drawn remarkable attention in the packaging industry because they are cheaper and more conductive than Au- and Cu-based wires, respectively. This study aimed to investigate the intermetallic compound (IMC) formation and growth at the bonding interface between Ag-4Pd wire and Al-pads and between Ag-8Au-3Pd wire and Al-pads. The as-bonded and reliability-tested Ag-4Pd/Al and Ag-8Au-3Pd/Al specimens were then investigated by transmission electron microscopy (TEM) and scanning transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (STEM-EDS). The bonding properties were examined by ball shear and wire pull tests. In the as-bonded state, hexagonal close-packed (HCP) (Ag, Pd)₂Al and HCP Ag₂Al were formed at the Ag-4Pd/Al interfaces, whereas dual phase consisting of face-centered cubic Ag alloy with HCP precipitates (Ag, Au, Pd)₂Al crystals and HCP Ag₂Al layers were observed at the Ag-8Au-3Pd/Al interfaces. The IMCs showed significant growth and oxidation during reliability tests at 130 °C and 85 pct relative humidity for 192 hours. Alloying Au in Ag-4Pd wires promoted the growth of the IMC layer and it also enhanced the mechanical properties in the as-bonded material. By contrast, overgrowth of the IMCs in the Ag-8Au-3Pd/Al system induced microcrack formation in bonding and thus degraded the reliability of the material.     

Influence of Zn Coating on Interfacial Reactions and Mechanical Properties During Laser Welding-Brazing of Mg to Steel

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.     

Bonding Strength and Grain Size Control of Dissimilar Joints of Al-Mg Alloys with Forge Welding

Metallurgical and Materials Transactions A - High-productivity dissimilar bonding between A2024 aluminum (Al) alloy and AZ80 magnesium (Mg) alloy with a pure titanium (Ti) interlayer was achieved...     

The diffusion bonding of Zr-2.5 pct Nb to steel

The diffusion bonding of zirconium-2.5 pct niobium to carbon steel with an interlayer of platinum has been investigated. Bonds were produced by heating samples in a furnace under compressive loading. Metallography of the bonds revealed that at both the Fe-Pt and the Pt-Zr/Nb interfaces, interdiffusion and the formation of thin bands of intermetallic phases occurred during bonding. The presence of FePt₃ was detected at the former interface and several intermetallics including Pt₃Zr at the latter. In both cases, intermetallic compound formation resulted in an increase in microhardness in the bond region; this was particularly severe at the Pt-Zr/Nb interface where cracking was observed to occur during, metallographic sample preparation. Bonding at temperatures above 1150 °C caused eutectic melting at the Pt-Zr/Nb interface.     

A Novel Bonding Method of Pure Aluminum and SUS304 Stainless Steel Using Barrel Nitriding

A great deal of research is being carried out on welding or bonding methods between iron and aluminum. However, it is not so easy to make Fe-Al bonding materials with both high strength and light weight. Recently, a new nitriding process has been proposed to produce aluminum nitride on an aluminum surface using a barrel. This study proposes a new concept in the production of a multilayer which has an AlN and Fe-Al intermetallic compound layer between the aluminum and steel using a barrel nitriding process. The bonding process was carried out from 893 K to 913 K (620 °C to 640 °C) for 18, 25.2, and 36 ks with Al₂O₃ powder and Al-Mg alloy powder. After the process, an aluminum nitride (AlN) layer and a Fe-Al intermetallic compound (Fe₂Al_5.4) layer were formed at the interface between the pure aluminum and SUS304 austenitic stainless steel. The thicknesses of the AlN layer and the intermetallic compound layer increased with increasing treatment temperature and time. The maximum hardnesses of the AlN layer and Fe₂Al_5.4 layers were found to be 377HV and 910HV, respectively, after barrel nitriding at 893 K (620 °C) for 18 ks.     

High-Productivity Forge Welding of AZ80 Magnesium Alloy to A2024 Aluminum Alloy Using an AC Servo Press

We have developed a high-productivity dissimilar bonding technology intended for the automobile sector, which is increasingly becoming multimaterial oriented. The forge-welding process, which involves diffusion bonding with plastic deformation in the open air, was used to bond AZ80 magnesium (Mg) alloy with A2024 aluminum (Al) alloy with a pure titanium (Ti) sheet interlayer using a high-speed, high-precision AC servo press. The influences of the preheat temperature, Ti sheet thickness, and the pressure holding time on the tensile strength were surveyed. In addition, the influence of the polishing of the bonding surfaces was examined. A pressure holding time of 0.1 seconds with a cycle time of less than 2 seconds provided high-strength bonding. Furthermore, a high-strength bond could be achieved with a Ti sheet thickness of only 0.3 mm and without needing polishing before bonding or heat treatment after bonding. Cross-sectional textures of the macro- and micro-fracture surfaces and elemental analyses of the bonded interface were examined. The fracture side of the bonded interface, the Ti-Mg alloy side, had a thin (ca. 5 nm) Ti-Al reaction layer (RL), which confirmed a diffusion bonding mechanism between the Ti and Al elements present in the Mg alloy. Despite processing in air with an extremely short processing time, this impacting press method provided good plastic deformability and sufficient elemental diffusion to result in high-strength bonding with a tensile strength ranging from 130 to 150 MPa.

     

Phase transformations at high pressures and temperatures and the structure of a hypoeutectic 1Ni-99Al alloy

The phase transformations in a hypoeutectic 1Ni-99Al alloy are studied by differential barothermal analysis in the temperature range up to 750°C at a compressed argon pressure up to ～100 MPa. The Al matrix of the initial alloy is found to be saturated by micropores at a concentration of 3.7 × 10¹⁰ cm^?3. After melting and solidification in a compressed argon atmosphere, the micropore concentration increases to 3.2 × 10¹¹ cm^?3. As a result of melting and solidification at a high pressure, the initial fine-grained structure of the alloy with an average grain size of 16 μm transforms into a coarse-grained structure during dendritic solidification. The processing of electron-microscopic images is used to determine the volume content of intermetallic compound Al₃Ni in the Al matrix. The liquidus temperature of the alloy at 100 MPa increases by 10°C, and the solidus temperature is 5°C higher than the eutectic transformation temperature in aluminum-rich Al-Ni alloys. The solid-phase decomposition of the supersaturated solid solution of nickel in aluminum occurs at 630°C. At 100 MPa, the field of solid solutions of nickel in aluminum extends to 1.2 at % Ni as compared to the Al-Ni system at atmospheric pressure. The lattice parameters of Al and Al₃Ni are found to increase in the alloy solidified at 100 MPa. The microhardness of the Al matrix in the alloy is measured after a barothermography cycle. A portion of the Al-Ni phase diagram is proposed for a pressure of 100MPa in the nickel content range 0–4.3 at %.     

Friction Stir Lap Welding of Magnesium Alloy to Steel: A Preliminary Investigation

An initial study was made to evaluate the feasibility of joining magnesium alloy AZ31 sheet to galvanized steel sheet in a lap configuration using friction stir welding (FSW). Two different automotive sheet steels were used for comparative evaluation of the dissimilar joining potential: a 0.8 mm thick, electrogalvanized (EG) mild steel, and a 1.5 mm thick hot-dipped galvanized (HDG) high-strength, low-alloy (HSLA) steel. These steels were joined to 2.33 mm thick AZ31B magnesium sheet. A single FSW tool design was used for both dissimilar welds, and the process parameters were kept the same. The average peak load for the AZ31-1.5 mm steel weld joint in lap shear mode was found to be 6.3 ± 1.0 kN. For the AZ31-0.8 mm steel weld, joint strength was 5.1 ± 1.5 kN. Microstructural investigation indicates melting of the Zn coating present on the steel sheets, and subsequent alloying with the Mg sheet resulted in the formation of a solidified Zn-Mg alloy layer.     

An Experimental Study of Transient Liquid Phase Bonding of the Ternary Ag-Au-Cu System Using Differential Scanning Calorimetry

An experimental approach using differential scanning calorimetry (DSC) has been applied to quantify the solid/liquid interface kinetics during the isothermal solidification stage of transient liquid phase (TLP) bonding in an Ag-Au-Cu ternary alloy solid/liquid diffusion couple. Eutectic Ag-Au-Cu foil interlayers were coupled with pure Ag base metal to study the effects of two solutes on interface motion. Experimental effects involving baseline shift and primary solidification contribute to a systematic underestimation of the fraction of liquid remaining. A temperature program has been used to quantify and correct these effects. The experimental results show a linear relationship between the interface position and the square root of the isothermal hold time. The shifting tie line composition at the interface has been shown to affect the DSC results; however, the impact on the calculated interface kinetics has been shown to be minimal in this case. This work has increased the knowledge of isothermal solidification in ternary alloy systems and developed accurate experimental methods to characterize these processes, which is valuable for designing TLP bonding schedules.     

A Study on the Effect of Process Parameters on the Properties of Joint in TLP-Bonded Inconel 738LC Superalloy

Optimization of transient liquid phase (TLP)-bonding variables is essential to achieve a joint free from deleterious intermetallic constituents and with appropriate mechanical properties. In this study, TLP bonding of IN-738LC superalloy was performed using AMS 4777 filler metal. The influence of gap size and bonding parameters (temperature and time) was investigated on the joint microstructure and its properties. In cases where the holding time was insufficient for complete isothermal solidification, the residual liquid transformed to non-equilibrium eutectic microconstituents consisting of nickel-rich boride, chromium-rich boride, and γ solid solution phases. The eutectic width decreased with the increase of holding time and the increase in initial gap size resulted in thicker eutectic width in the samples bonded at the same temperature and for equivalent holding times. The time of complete isothermal solidification decreased with the increase in bonding temperature to 1100°C, which was consistent with the models based on the diffusion-induced solid/liquid interface motion. Microhardness and shear strength tests were used to investigate the mechanical properties of the bonds. In the bonding condition in which isothermal solidification was not accomplished completely, the eutectic constituent with the highest hardness in the bond region was the preferential failure source. The results showed that homogenized joints had the highest shear strength.     

Effect of chilling and cerium addition on microstructure and cooling curve parameters of Al–14%Si alloy

Abstract

Al–14%Si alloys, with and without cerium, were cast at varying cooling rates by solidifying them in a crucible and against chills. The effect of melt treatment and chilling on microstructure and cooling curve parameters of the alloy was assessed. Ce treated alloys solidified in clay graphite crucible at a slow cooling rate showed refinement of primary silicon and the formation of Al–Si–Ce ternary intermetallic compound. The addition of Ce to the alloy solidified against chills resulted in simultaneous refinement and modification of primary and eutectic silicon. Nucleation temperatures of both primary and eutectic silicon decreased on addition of cerium. The formation of the intermetallic compound decreased with increase in cooling rate, leading to the modification of the eutectic silicon. The increase in the degree of modification of the eutectic Si was associated with the decrease in the volume fraction of the intermetallic compound formed.     

Influence of Chemical Composition of Mg Alloys on Surface Alloying by Diffusion Coating

A recently developed technique of surface alloying by diffusion-coating has been used to produce coatings on Mg alloys with various Al and Zn contents. The experimental results show that both Al and Zn solutes in the alloy promote the diffusion of alloying elements through grain refinement of the substrate alloys and through reduction of diffusion active energy because of the reduction of melting temperature of the alloys. Therefore, the efficiency of surface alloying increases by diffusion coating. Thick, dense, uniform, and continuous layers of intermetallic compounds, which consist of a τ-phase layer and a β-phase layer, can be produced on the surface of various Mg alloys. The intermetallic compound layers not only have microhardness values that are 4 to 6 times higher than the substrate but also provide effective protection of the Mg alloys from corrosion in 5 pct NaCl solution at room temperature.     

Laser Keyhole Welding of Dissimilar Ti-6Al-4V Titanium Alloy to AZ31B Magnesium Alloy

Laser keyhole welding of Ti-6Al-4V titanium alloy to AZ31B magnesium alloy was developed, and the correlations of process parameters, joint properties, and bonding mechanism were studied. The results show that the offset from the laser beam center on AZ31B side to the edge of the weld seam plays a big role in the joint properties by changing the power density irradiated at the Ti–Mg initial interface. The optimal range of the offset is 0.3 to 0.4mm in the present study. Some lamellar and granular Ti-rich mixtures are observed in the fusion zone, which is formed by intermixing melted Ti-6Al-4V with liquid AZ31B. The maximum ultimate tensile strength of the joints reaches 266 MPa. Furthermore, the fracture surface consists of scraggly remaining weld metal and smooth Ti surface. The higher the failure strength, the smaller the proportion of smooth Ti surface to whole interface is. Finally, the bonding mechanism of the interfacial layer is summarized by the morphologies and test results of fracture surfaces.