Thin Intermetallic Layer Research Articles

An enhancement of the yield strength and hardness in the friction stir welding of AZ31/AA3105 joint

The objective of this research is to optimize the yield strength and hardness of AZ31/AA3105 joint during the single pass friction stir welding (FSW). For this purpose, Taguchi method was used to examine the influence of FSW parameters such as rotating speed, linear speed, advancing side and shoulder diameter on the hardness and yield strength of the welding. The microstructure of the joint has also been analyzed by optical and scanning electron microscopy (SEM) to evaluate the joint quality. The results of microstructure analysis indicated that a high quality joint with thin intermetallic layers obtained at rotating speed of 1100 rpm and linear speed of 30 mm/min. The optimization results indicated that the hardness (78.06 HV) and yield strength (129.2 MPa) can be improved simultaneously with the advancing side of Mg, rotating speed of 1100 rpm, linear speed of 30 mm/min, and shoulder diameter of 15 mm. The fracture surface of samples indicated that a combination of brittle and ductile fracture was occurred at rotating speed of 1100 rpm and linear speed of 30 mm/min, which improved the ductility and toughness. It was concluded from the obtained results that a high-quality joint with improved mechanical properties can be obtained between AZ31 and AA3105 alloys in the optimal conditions of FSW parameters.

Laser-induced alloy nanoparticles on Au-Sn thin layers

The paper analyses the process of Au-Sn alloy nanoparticles (ANPs) formation by laser-induced dewetting of thin intermetallic layers for the first time. Tests were carried out for several samples with different Au-Sn atomic ratios and different total layer thicknesses (7.5 and 15 nm). The initial parameters of the samples were verified by spectroscopic ellipsometry (SE). To develop the experiment, a nanosecond ytterbium fiber laser (Yb:glass) with a wavelength of 1064 nm was used. The study was carried out both with the use of single laser pulses as well as raster scanning of the given surface. The use of two modes allowed to determine the impact of key process parameters (including pulse energy, degree of pulse overlap and laser fluency) on the formation, evolution, morphology, distribution and chemical composition of the obtained structures. The optimal conditions for the formation of Au-Sn ANPs were established.The samples were analysed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The chemical composition was analysed by means of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The optical properties of the obtained ANPs were determined by spectroscopic ellipsometry and the morphology and chemical composition were examined by transmission electron microscopy (TEM).

Ultrasonic-Assisted Brazing of Titanium Joints Using Modified Al-Si-Cu Based Fillers: Brazing at Liquid—Semisolid States under Load

Brazing joints of Ti/Ti under ultrasonic vibration (USV) and compression load were investigated using optimized and modified filler alloys of Al-Si-Cu-(Ni)-(Sr) group prepared in the lab. Preliminary trails at semisolid to liquid states were conducted using the ready Al-Si-Cu-(Mg) alloy as a filler, then the brazing cycle was redesigned and enhanced according to the microstructural observations of the produced joints. USV assisted brazing at the semisolid state of low solid fraction was able to produce joints with round silicon morphology and granular α−Al, while at a high solid fraction, USV was only able to affect the silicon and intermetallic particles. Applying a compression load after ultrasonic vibration, at a designed solid fraction, was proved to be a successful technique for improving the quality of the joints by reducing the porosity, enhancing the soundness of the joint, and the diffusion at the interface. Based on alloy composition and the improved brazing cycle, joints of thin intermetallic layer and high shear strength (of 93 MPa average value) were achieved. The microstructures and the mechanical behavior were discussed based on the filler compositions and brazing parameters.

Preparation and deformation behaviour of multi-structural aluminium-coated steels

Multi-structural aluminium coatings were successfully fabricated on a steel substrate by a combination of magnetron sputtering and hot-dip aluminising to improve the formability of hot-dip aluminised steel. The deformation behaviour, formation mechanism and cracking failure of the multi-structural aluminium-coated steels (AlHD/AlMS-ST) were investigated through deep drawing. The coatings were composed of an outer Al layer and an inner FeAl intermetallic layer which consisted of a FeAl3 layer and a Fe2Al5 layer. Compared with hot-dip aluminised steels, AlHD/AlMS-ST presented a sparsely arranged comb-tooth structure and a reduction in thickness of the intermetallic layer. Results indicated that I-cracks, II-cracks and secondary cracks can be generated in the intermetallic layer, and punch corner and flat surface area were susceptible to fracture during deep drawing. I-cracks propagated in the direction perpendicular to the coating/substrate interface, whereas II-cracks propagated parallel to the coating/substrate interface. AlHD/AlMS-ST exhibited excellent resistance to crack propagation and formability because of the comb-tooth structure and thin intermetallic layer.

Pinless FSSW of DP600/Zn/AA6061 dissimilar joints

AA6061 alloy sheets have been successfully spot-welded to dual-phase DP600 steel sheets with pinless friction stir spot welding method. The Box-Behnken design of experiments was implemented to arrange the tests. The individual and interaction effect of each process parameter on the lap-shear failure load of the joints was investigated. The maximum failure load of 4.4 kN was achieved at 1300 rpm rotational speed, 2000 kg axial force, and 10 s welding time. Microstructural features of the interfaces and phase evolution were studied by scanning electron microscope and X-ray diffraction, respectively. The bonding mechanisms at the joint interface are classified into two types: thick intermetallic layer (type I), and thin intermetallic layer with thick Zn–Al diffusion region (type II) in the aluminum/steel interface.

Mechanical Parameters Response on Micro-Friction Stir Welding of AA6061 and SS304 Sheets

Friction stir welding is a contact welding process that uses the heat generated by friction to fuse two different materials. This work is focused on the development of micro-friction stir welding which is carried out for very thin sectioned materials of thickness 1000[Formula: see text][Formula: see text]m or less. Friction welded butt-joints were successfully produced for 0.8[Formula: see text]mm thin AA6061 and SS304 sheets on a semi-automated vertical milling machine using a zero-pin length tool. A mild steel backing plate is used as fixture mechanism to hold the welding sheets on machine. Tool-rotational speed and Tool-travel speed are the weld-parameters examined on mechanical responses such as tensile behavior, micro-hardness and surface-roughness across the nugget-weld zone interface. The maximum tensile strength is obtained at lower weld-parameters. Tensile strength properties of AA6061-T6/SS304 joints were approximately found to be 25% lower than that of the AA6061-T6 alloy base metal. Maximum hardness value of 93HV and minimum roughness value of 2.808[Formula: see text][Formula: see text]m are observed for higher tool speeds at nugget-weld zone interface due to the formation of intermetallic phases. Microstructural behavior is studied on weld-parameters using scanning electron microscope and energy dispersive X-ray analyzer. Very thin intermetallic layers (consisting of Fe2Al5, FeAl3 and FeAl2 phases) were observed in stainless steel/aluminum interface.

Bond shear strength of Al2O3 nanoparticles reinforced 2220-capacitor/SAC305 solder interconnects reflowed on bare and Ni-coated copper substrate

The influence of Al2O3 nanoparticles addition in trace amounts and electroless Ni–P substrate coating on the microstructure development and bond shear strength of Sn-3.0Ag–0.5Cu (SAC305) solder joint were investigated. The performance and reliability of the 2220-capacitor joints with Al2O3 nanoparticle reinforced nanocomposites reflowed on Cu and Ni–P coated substrate were analyzed under varying high-temperature environments. The addition of nanoparticles enhanced the wettability and microhardness of the solder and considerably refined the joint microstructure. The dispersion and adsorption of Al2O3 nanoparticles resulted in the suppression of intermetallic (IMC) growth at the interface and refinement of the β-Sn grains as well as IMC precipitates into the matrix. The Ni–P coating on the substrate significantly retarded the IMC growth kinetics resulting in the formation of a thin and uniform IMC layer at the joint interface. The thermal stability and performance of the joint under high-temperature environments were enhanced due to the Ni–P coating on the substrate. Compared to the unreinforced SAC305 solder joint with bare Cu substrate, joints with SAC305 + 0.05Al2O3 composite showed about 17% higher shear strength with bare Cu substrate and about 27% higher strength with Ni–P coated substrate. The Weibull distribution analysis indicates a significant improvement in joint reliability of the 2220-capacitor/SAC305 solder assembly using SAC305 + 0.05Al2O3 nanocomposite and Ni-coated substrate. The ANOVA study suggests that the solder joint performance majorly depends on the operating environment, solder composition, and the substrate finish.

Die Soldering Behavior of H13 and Cr-Mo-V Tool Steel on Die Casting Process on Nitriding-Shot Pinning Die Surface Treatment

Die soldering is a sticking phenomenon between molten aluminum with the surface of steel die in the die casting process, which results in damage to the cast products and l the steel die. In this research, two die materials, H13 and Cr-Mo-V steels were used. Those dies were then treated by two process variables, shot pinning and nitriding-shot pinning. To simulate the die casting process, the samples were dipped into molten Aluminum-Si alloy, ADC12 at 680oC for 30, 300, and 1800 seconds. Characterizations were focused on the surface of the steel, which includes microstructure observation by a microscope, microhardness profile, compound identification, and weight loss measurements. It was found that H13 steel and Cr-Mo-V steel treated by nitriding–shot pinning have higher hardness up to 100% and thinner intermetallic layer. On H13 steel, the compact layer thickness decreased from 19 μm to 17 μm and from 96 μm to 80 μm for the broken layer. Similar trends occurred for Cr-Mo-V steel, where the thickness of the compact layer and broken layer decreased from 38 μm to 19 μm and 119 μm to 45 μm respectively. These results indicate that H13 and Cr-Mo-V steels that were treated by nitriding–shot pinning have a better resistance to die soldering.

Studies on the characterization and morphological features of the coating on interstitial free steel dipped in molten Al-Si-Mg alloy at 800 °C

Interstitial-free (IF) steel specimens were coated by hot-dip aluminizing process bearing bath composition as Al-6.9% Si-1.4% Mg and bath temperature at 800°C. Dipping time varied for 0.5, 1, 3 and 6min. The objective of the present study is to conduct a systematic investigation to identify and analyse the formation of various phases and compounds in the coating. Studies on aluminizing of steel had indicated the presence of an intermetallic layer adjacent to steel substrate. In this study, the morphological features obtained after hot dipping at 800°C were investigated. For the application of aluminized steel sheets in industry for manufacture of tubes and pipes, the adherence of the aluminized coating must be ensured. This property of the coating is influenced by the morphological features of the coating. Aluminizing being thought of a possible substitution of galvanizing owing to its promise to evolve lesser volume fraction of intermetallic phases and consequently known to generate a ductile coating. The entire coating consists of an outer Al-Si topcoat and a thin intermetallic layer which composed of an outer θ-FeAl3 and inner η-Fe2Al5 layers. The thickness of intermetallic layers was found to increase with the increase of dipping time in a near parabolic manner.The phases formed on the IF steel substrates were characterized by scanning electron microscopy with EDS, X-ray diffraction, EPMA and EBSD techniques.Interesting findings from XRD include the presence of Al3FeSi2 (τ4) and Al2FeSi (τ3) phases, which normally appear after annealing of aluminised sheet. A distinct elemental Si peak was found in XRD study. Presence of Mg in the form of Mg2Si was also found in XRD and supported by EPMA investigation. Presence of several ternary Al-Fe-Si (τ3, τ4, τ5) and binary FeAl3 and Fe2Al5intermetallic phases were identified by composition profile analysis from SEM based EDS and GDOES and further confirmed by EBSD. Presence of Si humps in the top and intermetallic layer attributed by the presence of Si-bearing phases or elemental pro-eutectic Si in Al-Si alloy were also indicated in SEM-EDS and GDOES study. Variation of surface topographical features of the HDA steel substrates with increasing dipping durations were examined and reported for the first time by using AFM. Formability tests were conducted by bending the samples 180° over a mandrel. None of the specimens showed any tendency of flaking exhibiting excellent bonding of the coating with IF steel substrate.

Influences of shape of the new interfaces and morphology of the intermetallics on mechanical properties of aluminum AA2024–pure copper joints by friction stir welding

Friction stir welding (FSW) joints are inevitably accompanied with the change in shape of the abutting surfaces due to the tool movement. Further, the formation of brittle intermetallics (during dissimilar welding) is also unavoidable. Therefore, the current work is focused to study the role of the shape of the new interface in properties of the joints and to control the morphology of intermetallics subsequently. FSW experiments were carried out between aluminum AA2024 and pure copper for different tool offset positions (on either side of the interface), plate positions (copper in advancing or retreating side), and tool geometry (plain and threaded). The microstructure observation showed noticeable changes in the shape of the new interface with respect to the selected parameters. Tensile tests highlighted that the weld which has continuous and smooth new interface gave better properties than the welds which had an irregular discontinuous interface. Also, this kind of interfaces had formed with a continuous thin intermetallic layer, and it was a desirable morphology of the intermetallics. The weld with this thin intermetallic layer (metallurgical bonding) alone has the maximum strength, whereas the welds that also had fine steps at the interface (mechanical bonding from interlocking effect) have maximum ductility. The mechanism behind this was explained in detail with the help of material flow behavior study for the selected conditions. This concluded that to achieve better properties, the shape of the new interface and the bonding along this interface are mainly important to be considered.

Junction growth and interdiffusion during ultrasonic additive manufacturing of multi-material laminates

Ultrasonic additive manufacturing is a promising approach for making net-shaped multi-material laminates from material combinations difficult to process with fusion-based additive manufacturing techniques. The properties of these multi-material laminates depend sensitively on the interface between the constituents, which can be decorated with pores as well as thin intermetallic layers. Here, we develop process models for junction growth and interdiffusion during ultrasonic additive manufacturing of dissimilar metals. These process models are validated against published experimental data, then used to generate process diagrams which reveal that high normal loads and high sonotrode velocities can reduce intermetallic growth while maintaining strong interlayer bonding.

Mechanical and metallurgical properties of friction stir welded dissimilar joints of AZ91 magnesium alloy and AA 6082-T6 aluminium alloy

Abstract In the present research work, AZ91 magnesium alloy and AA6082-T6 aluminium alloy were joined by friction stir welding process. The comparison of microstructure and mechanical properties between different joints by varying the different materials on advance and retreating sides were mainly studied. Four different welds have been prepared to find the material mixing between the similar and dissimilar joints. The joint interfaces of the welds have been investigated by employing an optical microscope and scanning electron microscope. When Mg was placed on advancing side (AS), more aluminium content was soluble in nugget zone than the case where Mg was placed on the retreating side (RS). Thin intermetallic layer in the joint interface of Mg/Al and thick intermetallic layer with poor adhesion of the aluminium and magnesium have been observed in the dissimilar joints varying the sides. The highest UTS of 172.3 MPa was found for Mg-Al when Mg was placed on AS and lower UTS of 156.25 MPa was obtained when Mg was placed on RS. Hardness of 86 Hv and 89 Hv were observed in the Stir zone for the dissimilar AZ91 Mg alloy and AA6082-T6 Al alloy when AZ91Mg alloy was placed on the AS and on the RS respectively. Fractography was also carried out to find the mode of failure.

Influence of the structure and phase composition of the bond interface on aluminium–copper lap welds strength

ABSTRACTThe structure and phase composition of the bond interface of aluminium–copper lap welds produced by friction stir welding and tool-assisted friction welding were analysed. Microstructural analysis proved that no through-interface material flow took place in tool-assisted friction welding and that aluminium–copper joining resulted from the formation of a thin and continuous intermetallic layer at the lap interface. For the welds produced by friction stir welding, evidences of through-interface material flow were found, promoting mechanical interlocking of both base materials, at the lap interface, and formation of discontinuous intermetallic layers. Mechanical testing showed that the tool-assisted friction welds, with excellent surface finishing, had low strength, contrary to the friction stir welds, which displayed excellent bond strength. The comparison of the mechanical and microstructural results, for both weld types, pointed to the ineffectiveness of the continuous intermetallic layer in providing high strength bonding.

Dissimilar Metal Joining of A5052 Aluminum Alloy and AZ31 Magnesium Alloy Using Laser Brazing

The microstructure and mechanical properties of a joint produced by laser brazing between A5052 and AZ31 with AZ61, AZ91 and AZ125 filler metal was investigated. The effects of filler metals on joint characteristics are also discussed. Measurement of microstructural factors in the laser brazed joint revealed that increasing the laser power results in a decrease in the weld toe angle and an increase in the bead width, which indicates superior wettability. A high strength laser brazed joint can be achieved through the combination of good wettability and a thin intermetallic layer produced by a laser power of 590 W in a brazed joint with AZ125 filler metal Any further increase in power, however, results in a rapid increase in the thickness of the intermetallic compound (IMC) reaction layer. The superiority of the brazed joint with AZ125 filler metal is due to its lower melting point than that of AZ61 and AZ91 filler metal.

Microstructural characteristics and mechanical properties of the dissimilar friction-stir butt welds between an Al–Mg alloy and A316L stainless steel

In this research, dissimilar butt joining of an Al–Mg alloy (AA5083) to austenitic stainless steel (A316L) by using friction-stir welding (FSW) process was examined. FSW parameters and joint design were optimized, owning to achieve the best joint strength. The processed FSWs at the optimized traverse speeds of 16, 20, and 25 mm/min with the sound surface appearance were considered for further cross-sectional investigations, microstructural characterizations, and mechanical testings. In situ reactions at the interface of Al–Mg alloy and stainless steel during FSW processes were studied by using field emission-scanning electron microscopy (FE-SEM) and line-scan energy-dispersive X-ray spectroscopy (EDS) analysis. As expected from the monitored thermal histories during FSW joining, the features indicating the formation of tunneling like defects were observed at low heat inputs (low w/v ratios). Moreover, some discontinuous thin intermetallic layers (with the thickness of ∼0.5 μm) were formed at the joint interface at the expressed processing conditions. Mechanical performances of the prepared dissimilar joints were assessed during transverse tensile loading and Vickers indentation micro-hardness testing. The joint strength ratio to the ultimate tensile strength (UTS) of the weakest base metal (BM) was improved up to ∼93 %, as all of the dissimilar FSWs failed from the Al–Mg base alloy, with a Vickers hardness enhancement of ∼460 % at the interface.

Laminated Ti-Al composites: Processing, structure and strength

Laminated Ti-Al composite sheets with different layer thickness ratios have been fabricated through hot pressing followed by multi-pass hot rolling at 500°C.The laminated sheets show strong bonding with intermetallic interface layers of nanoscale thickness between the layers of Ti and Al. The mechanical properties of the composites with different volume fractions of Al from 10% to 67% show a good combination of strength and ductility. A constraint strain in the hot-rolled laminated structure between the hard and soft phases introduces an elastic-plastic deformation stage, which becomes more pronounced as the volume fraction of Al decreases. Moreover, the thin intermetallic interface layer may also contribute to the strength of the composites, and this effect increases with increasing volume fraction of the interface layer.

Experimental analysis of bonding strength in shape rolling of Al–Cu bimetallic circular pipes into square tubes

In the present research, the intermetallic layer situation and bond strength of square tubes produced by shape rolling of Al–Cu bimetallic pipes has been investigated. The explosive welding process was used for the production of bimetallic circular pipes. The macro- and microscopic features of explosive-welded pipes and shape-rolled specimens at various stages were experimentally measured by using shear and hardness testing and optical metallography. Moreover, scanning electron microscopy was used for fractography of the fracture surfaces after the last stage of forming. The experimental results showed that the shear strength variation is dependent on the intermetallic layer thickness and its continuity. Also, continuity in Al–Cu interfaces that have a thick intermetallic layer intensifies the microcrack propagation, while due to discontinuity in the thin intermetallic layer, the retardation of catastrophic crack propagation was observed in the early passes of the shape-rolling process. However, the results of the present study showed that as the passes proceed in the rolling process, the crack propagation phenomenon, which is the cause of a decrease in shear strength, is expected.

Characterisation of Al–Ti dissimilar material joints fabricated using ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid state manufacturing process for joining thin metal tapes using principles of ultrasonic metal welding. The process operates at low temperatures, enabling dissimilar material welds without generating harmful intermetallic compounds. In this study, a 9 kW UAM system was used to create joints of Al 1100 and commercially pure titanium. Viable process parameters were identified through pilot weld studies via controlled variation of weld force, amplitude and weld speed. Push-pin delamination tests and shear tests were performed, comparing as-built, heat treated and spark plasma sintering treated samples. Heat treated and spark plasma sintering treated samples yielded mechanical strengths over twice that of as-built samples. Electron backscatter diffraction measurements show that deformation and grain refinement only take place in the aluminium layers. Heat treated samples exhibit a thin intermetallic layer, which is hypothesised as constraining the interface, leading to the improved strength.

Effect and controlling mechanism of vanadium on Fe–Al interface reaction in Al–Zn bath

Abstract The influence of vanadium on Fe–Al interface reaction of steels during hot-dip process was investigated by immersing low carbon steel plates into six different Al and Al–Zn baths at 730 °C and 620 °C. The microstructure and phase constituent of the formed coatings were analyzed with SEM–EDS and XRD. The intermetallic layers formed on the steel plate surfaces in Al bath consist of Fe2Al5 and FeAl3 phases. As 0.05 wt.% V was added to the Al bath, the Fe2Al5 layer became thinner. Whereas the steel plates were immersed into 55%Al–Zn bath, a periodic laminar structure, containing FeAl3 and Al–Zn phases, formed. However, the periodic laminar structure disappeared and a continuous thin Fe2Al5 layer appeared as V was added into Galvalume bath, and the whole intermetallic layer consists of Fe2Al5, Fe2Al8Si and FeAl3 phases. The presence of 0.05 wt.% V in the bath promoted the formation of Fe2Al5 layer. As it covers the whole steel plate surface, it retards the further Fe–Al reaction in the bath, leading to a thin intermetallic layer. The influence of V on Fe–Al interface reaction was studied by means of Vienna Ab-initio Simulation Package (VASP) based on first-principles method. The exchange energy, bonding energy, charge density differences and electronic density of states of Fe2(Al,V3)5 and Fe(Al,V12)3 are analyzed. Both the experimental results and theoretical calculation results show that V could occupy the vacancies of Fe2Al5 lattice which could promote the nucleation of Fe2Al5, and therefore it suppresses the growth of Fe–Al phase.

Effects of ball milling and particle size on microstructure and properties 5083 Al–Ni composites fabricated by friction stir processing

Ni particles were incorporated in a 5083 Al alloy matrix by friction stir processing (FSP) to fabricate metal particle reinforced composite. During the optimization of the process parameters for uniform particle distribution, it was found that ball-milled finer particles (10μm) were dispersed more uniformly in the matrix compared to as-received coarse particles (70μm). Hence, the particles were ball-milled before incorporating into 5083 Al matrix. The finer ball-milled particles were dispersed uniformly, however a thin intermetallic layer was formed at the particle-matrix interface. The layer was found to be Al–Ni intermetallic. When as-received fine particles of similar size (10μm) were incorporated using the same FSP parameters no such layer was observed in the processed composite. Hence, ball milling of particles influenced the microstructure of the composite. The high-energy state of the ball-milled particles can be attributed to the formation of the interfacial layer. The strength of both the composite was higher compared to the unreinforced 5083 Al alloy. FSP also refined the grain size of the aluminum matrix from 25µm to 3.5µm and this also contributed to the strength enhancement of the composites. The strength and ductility of the ball-milled composite were lower as expected compared to the composite with as-received fine Ni particles due to the presence of the interfacial reaction layer.