Microstructural evolution and mechanical properties of dissimilar Al–Cu joints produced by friction stir welding

5A02 aluminum alloy and pure copper were joined by friction stir welding (FSW). A defect-free joint was obtained when one of process parameters, i.e. the traverse speed was lowered from 40 mm/min to 20 mm/min. A good mixing of Al and Cu was observed in the weld nugget zone (WNZ). A large amount of fine Cu particles were dispersed in the upper part of the WNZ producing a composite-like structure. In the lower part, nano-scaled intercalations were observed and identified by transmission electron microscopy (TEM). These layered structures were subsequently confirmed as Al₄Cu₉ (γ), Al₂Cu₃ (ε), Al₂Cu (θ), respectively. Formation of these microstructures caused an inhomogeneous hardness profile. Particularly, a distinct rise in hardness was noticed at the Al/Cu interface. Excellent metallurgical bonding between Al and Cu gave rise to good behaviors in the tensile and bending strength.     

Characterization of microstructure and mechanical properties of Al–Cu–Mg–Ag–(Mn/Zr) alloy with high Cu:Mg

This study examines the effects of the addition of Mn or Zr on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy using optical microscopy, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, transmission electron microscopy, tensile test, and tear test. The results showed that the alloy with Zr exhibited the highest strength and the lowest fracture toughness, which may be attributed to the segregation of the secondary phases containing the Zr element on the recrystallization grain boundaries. The alloy with Mn exhibited strength that is roughly equal to the Al–Cu–Mg–Ag alloy and the highest fracture toughness, which may be due to the formation of secondary phases containing Mn and Fe elements. Mn or Zr addition also has no remarkable influence on the characteristics of the precipitates. The Ω phase and a small quantity of θ′ phases dominated the microstructure of the three alloys after aging.     

Comparative study on microstructure and mechanical properties of laser welded–brazed Mg/mild steel and Mg/stainless steel joints

A laser welding–brazing (LWB) technology using Mg based filler has been developed for joining Mg alloy to mild steel and Mg alloy to stainless steel in a lap configuration. Microstructure and mechanical properties of laser welded–brazed lap joints in both cases were comparatively studied. The results indicated that no distinct reaction layer was observed at the interface of Mg/mild steel and subsequently the interface was confirmed as mechanical bonding, whereas an ultra thin reaction layer with a continuous and uniform morphology was evidenced at the Mg/stainless steel interface, which was indicative of metallurgical bonding. The newly formed interfacial layer was indexed as FeAl phase by transmission electron microscopy (TEM) combined with energy dispersive spectroscopy (EDS). The average tensile–shear strength of Mg/mild steel joint was only 142 N/mm with typical interfacial failure, while that of Mg/stainless steel joint could reach 270 N/mm, representing 82.4% joint efficiency relative to the Mg alloy base metal. The fracture location of Mg/stainless steel joint was at Mg fusion welding side, suggesting the interface was not weak point due to the formation of ultra thin interfacial layer. The role of alloying elements in base metal and bonding mechanism of the interfacial layer were discussed, respectively.     

Effect of Al foils interlayer on microstructures and mechanical properties of Mg–Al butt joints welded by gas tungsten arc welding filling with Zn filler metal

Gas tungsten arc butt welding of Mg–Al filling with Zn filler metal without and with Al foils in different thicknesses was carried out. Additional Al element was introduced into the fusion zone to accurately modulate microstructure and composition of the welding seam. Microstructures and mechanical properties of the welded joints were examined. Results show that the addition of appropriate quantity of Al element increases the content of Al-based solid solution in the fusion zone near the Mg base metal. The solid solution can eliminate the stress concentration and hinder crack propagation, so the tensile strengths of the joints are improved. However, the immoderate quantity of Al element will lead to the formation of partially Al-rich zones and deteriorate the mechanical property of the joints.     

Investigation of microstructure and mechanical properties of steel fibre–cast iron composites

Abstract

The aim of the present experimental study was to investigate improvement of the toughness and strength of grey cast iron by reinforcing with steel fibres. The carbon content of the steel fibres was chosen to be sufficiently low that graphite flakes behaving as cracks were removed by carbon diffusion from the cast iron to the steel fibres during the solidification and cooling stages. To produce a graphite free matrix, steel fibres with optimum carbon content were used and the reinforced composite structure was cast under controlled casting conditions and fibre orientation. Three point bend test specimens were manufactured from steel fibre reinforced and unreinforced flake graphite cast iron and then normalising heat treatments were applied to the specimens at temperatures of 800 and 850°C. The fracture toughness and strength properties of the steel fibre reinforced material were found to be much better than those of unreinforced cast iron. The microstructures of the composite at the fibre–matrix transition zone were examined.     

Interfacial microstructure and mechanical strength of WC–Co/90MnCrV8 cold work tool steel diffusion bonded joint with Cu/Ni electroplated interlayer

An important challenge in the design and processing of engineering materials is to combine incompatible properties of materials in the same component. One of the most common processes for joining dissimilar materials is brazing, but as a result of the poor resistance of the joints in service at high temperatures, diffusion bonding is proposed as the best suited alternative bonding process. In the present investigation, a cemented carbide (WC–15%Co) and a cold work tool steel (90MnCrV8) have been diffusion bonded in vacuum, using a ductile interlayer. Effects of the bonding time (30–60 min) and temperature (825–850 °C) on the quality of diffusion bonding interfaces were studied. The maximum tensile strength obtained confirms a very promising technology for industrial applications.     

Effect of Cu/Zn on microstructure and mechanical properties of extruded Mg–Sn alloys

In this paper, the effect of Cu and Zn addition on mechanical properties of indirectly extruded Mg–2Sn alloy was investigated. Mg–2Sn–0.5Cu alloy exhibits a moderate yield strength (YS) of 225?MPa and an ultimate strength of 260?MPa, which are much higher than those of the binary Mg–2Sn alloy, and the elongation (EL) evolves as ～15.5%. Mechanical properties of the Mg–2Sn–0.5Cu alloy are deteriorated with more 3 wt-% Zn addition, and YS and EL are reduced as 160?MPa and ～10%. The detailed mechanism is discussed according to the work-hardening rate and strengthening effect related to the grain sizes, second phases and macro-textures. Grain refinement and proper texture are believed to play a critical role in both strength and ductility optimisation.     

Effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy

The effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), differential scanning calorimeter (DSC), transmission electron microscopy (TEM) and tensile test, respectively. The results show that the mechanical property increases and then decreases with increasing the solution temperature. And the residual phases are dissolved into the matrix gradually, the number fraction of the precipitation and the size of recrystallized grains increase. Compared to the solution temperature, the solution holding time has less effect on the microstructure and the mechanical properties of Al–Cu–Mg–Ag alloy. The overburnt temperature of Al–Cu–Mg–Ag alloy is 525 °C. The yield strength and the elongation get the best when the alloy is solution treated at 515 °C for 1.5 h, is 504 MPa and 12.2% respectively. The fracture mechanism of the samples is ductile fracture.     

Effect of friction welding parameters on mechanical and metallurgical properties of aluminium alloy 5052–A36 steel joint

Abstract

The mechanical and metallurgical properties of friction welded joints between type 5052 aluminium alloy and type A36 steel have been studied in the present work. Joint strength increased with increasing upset pressure and friction time until it reached a crictical value. The strength of the joint settled at a lower value, compared with that of the base metal, in the case of increasing friction time, caused by the formation of an intermediate phase (intermetallic compound, oxides). The microstructure of 5052 alloy was greatly deformed near the weld interface, and underwent dynamic recrystallisation owing to frictional heat and deformation resulting from the friction welding process. Therefore, a very fine and equiaxed grain structure was observed near the interface. Elongated grains were observed outside the dynamic recrystallisation region at the peripheral part, while the A36 steel side was not deformed. The hardness of the near interface was slightly softer than that of the 5052 alloy base metal, and maximum softened width was ~8 mm from the interface. In the present work, the conditions of friction time t ₁ = 0.5 s and upset pressure P ₂ = 137.5 MPa gave maximum joint strength of 202 MPa when the friction pressure, upset time and rotation speed were fixed at 70 MPa, 5 s and 2000 rev min^-1, respectively, and these were the optimum friction welding conditions for the aluminium alloy 5052-A36 steel joint.     

The microstructure and mechanical properties of fluxless gas tungsten arc welding–brazing joints made between titanium and aluminum alloys

Butt joining of a titanium alloy to an aluminum alloy by gas tungsten arc welding–brazing using an Al-Si eutectic filler wire without flux is investigated. The butt joints have dual characteristics, being a welding on the aluminum side and a brazing on the titanium side. The thickness of the reaction layer varies with position in the titanium alloy interfacial area of the joint, ranging from 2 to 5 μm. At the upper part of interfacial area, the reaction layer includes only the rod-like TiAl₃ phase with 10 at.% dissolved Si. At the bottom of interfacial area, the reaction layer consists of the needle-like τ1 phases (Ti₇Al₅Si₁₂) and the block-like TiAl₃ phase. Hardness of the reaction layer near the welded seam/Ti alloy interface was as much as 400–500 HV. The highest tensile joint strength observed was 158 MPa. Tensile joint failure was by cracks initiating from the reaction layer at the bottom of the joint propagating into the welded seam at the upper part of the joint.     

Effects of Cu content on microstructure and mechanical properties of Al–14.5Si–0.5Mg alloy

This study elucidates how Cu content affects the microstructure and mechanical properties of Al–14.5Si–0.5Mg alloy, by adding 4.65 wt.% and 0.52 wt.% Cu. Different Fe-bearing phases were found in the two alloys. The acicular β-Al₅FeSi was found only in the high-Cu alloy. In the low-Cu alloy, Al₈Mg₃FeSi₆ was the Fe-bearing phase. Tensile testing indicated that the low-Cu alloy containing Al₈Mg₃FeSi₆ had higher UTS and elongation than the high-Cu alloy containing the acicular β-Al₅FeSi. It is believed that the presence of the acicular β-Al₅FeSi in the high-Cu alloy increased the number of crack initiators and brittleness of the alloy. Increasing Cu content in the Al–14.5Si–0.5Mg alloy also promoted solution hardening and precipitation hardening under as-quenched and aging conditions, respectively. The hardness of the high-Cu alloy therefore exceeded that of low-Cu alloy.     

Effect of cooling aging on microstructure and mechanical properties of an Al–Zn–Mg–Cu alloy

In the present work, Al–Zn–Mg–Cu alloy was aged by non-isothermal cooling aging treatment (CAT). At high initial aging temperature (IAT), the hardness was decreased with the decreased cooling rate. However, when IAT was lower than 180 °C, the hardness was increased with the decreased cooling rate. Conductivity was increased with the decreased cooling rate regardless of IAT. The tensile strength, yield strength and conductivity of Al alloy after (200–100 °C, 80 °C/h) CAT were increased 2.9%, 8.1% and 8.3% than that after T6 treatment, respectively. With an increase of IAT and decrease of cooling rate, the fine GP zone and η′ phase were transformed to be larger η′ and η precipitates. Moreover, continuous η phase at grain boundary was also grown to be individual large precipitates. Cooling aging time was decreased about 90% than that for T6 treatment, indicating cooling aging could improve the mechanical properties, corrosion resistance and production efficiency with less energy consumption.     

Non-isothermal aging of a high-Zn-containing Al–Zn–Mg–Cu alloy: microstructure and mechanical properties

The non-isothermal aging behaviour of a newly developed Al–Zn–Mg–Cu alloy containing 17?wt-% Zn was investigated. Hardness and shear punch tests demonstrated that during non-isothermal aging, the mechanical properties of the alloy first increased and then decreased. The best properties were obtained in a sample which was non-isothermally aged upto 250°C with heating rate of 20°C?min^?1, due to the presence of η′/η (MgZn₂) phases. This was confirmed by differential scanning calorimetery. After homogenisation, residual eutectic phases remained at triple junctions or in a spherical form. During aging, these phases transformed into rodlike S (Al₂CuMg)-phase at 400°C, with sizes ranging from 50 to 250?nm. The precipitation sequence in this high-Zn alloy was similar to that for conventional Al–Zn–Mg–Cu alloys.     

Microstructure and mechanical properties of molybdenum–iron–boron–chromium cladding using argon arc welding

The molybdenum–iron–boron–chromium claddings with different Mo/B atomic ratios were produced on Q235 steel using argon arc welding. The microstructure and crystalline phases were studied by optical microscopy, scanning electron microscopy and XRD. In addition, the formation mechanism of hard phase was investigated by thermodynamic calculations and phase diagrams. The results showed that the claddings were composed of the Mo₂FeB₂, M₃B₂ (M: Mo, Fe and Cr) hard phases and σ-FeMoCr solid solution. In addition, calculated results revealed that the M₃B₂, MB and σ-FeMoCr were successively precipitated from the melting pool. Moreover, the maximum microhardness value of the cladding was about 1600 HV_0.5. Wearing test indicated that claddings of lower Mo/B ratios have better wear resistance.     

Microstructure and mechanical properties of friction spot welding aluminium–lithium 2A97 alloy

In this study, we investigated the microstructure and mechanical properties in different regions of the friction spot welded 2A97 aluminium–lithium alloy subjected to different heat treatment processes. The 2.0 mm thick hot-rolled sheet of 2A97 alloy was successfully welded using friction spot welding method with optimised welding parameters. Afterwards, the as-welded 2A97 joints experienced two subsequent heat treatment procedures: solution and ageing; directly ageing. The corresponding microstructure and mechanical properties of the heat-treated specimens were studied by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), hardness test and tensile test. The results show that the mechanical properties of the 2A97 joints before and after heat treatment were significantly modified, which was mainly related to fine-grained microstructure, size and type of precipitates, and dislocation density. Compared to the base material and the material that only experienced direct ageing, the whole friction spot welded 2A97 joint after solution and ageing treatment delivered better mechanical properties.     

Effect of welding parameters on microstructure and mechanical properties of friction stir welded joints of a super high strength Al–Zn–Mg–Cu aluminum alloy

Samples made of a super high strength aluminum alloy with high Zn content were friction stir welded with rotation rates of 350–950 rpm and welding speeds of 50–150 mm/min. The effect of welding parameters on the microstructure and mechanical properties was investigated. It was observed that the grain size of the nugget zones decreased with the increasing welding speed or the decreasing tool rotation rate. Most of the strengthening precipitates in the nugget zone were dissolved back and the intragranular and grain boundary precipitates in the heat affected zone coarsened significantly. The greatest ultimate tensile strength of 484 MPa and largest elongation of 9.4 were obtained at 350 rpm−100 mm/min and 350 rpm−50 mm/min, respectively. The ultimate tensile strength and elongation deteriorated drastically when rotation rate increased from 350 to 950 rpm at a constant welding speed of 100 mm/min.     

The effects of Mg amount on the microstructure and mechanical properties of Al–Si–Mg alloys

In this study, the effects of magnesium (Mg) addition to A356 aluminum alloy at different amounts on the microstructure and mechanical properties of this alloy were examined. For the experimental studies, three different alloys (0.43, 0.67 and 0.86 wt%) having various amounts of Mg were prepared through casting process in the form of plates. The plates were homogenized and cooled in the furnace. All the samples were treated with aging process (T6) and then tensile samples were prepared from the homogenized samples. The samples treated with T6 process were characterized by optical microscopy, laser confocal microscopy, Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS) and X-Ray Diffraction (XRD) examinations as well as hardness measurements and tensile tests. The phases which were formed in the microstructures for different amounts of Mg were examined. It was observed that iron-rich intermetallic compounds were also formed in addition to the phases resulting from the aging process. Fe-rich intermetallic compounds, observed from the fracture surfaces, were found to reduce the tensile strength the alloy. The results also indicate that the tensile strength and hardness of the alloy increase with increasing Mg amount.     

Ultrasonic spot welding of aluminium to steel for automotive applications—microstructure and optimisation

Energy efficient methods for joining aluminium to steel have potential for major applications in the automobile industry. Results are reported where 1 mm gauge 6111 aluminium and DC04 steel automotive sheet have been successfully joined using the novel process of high power ultrasonic spot welding. The microstructure and performance of the joints were examined, as a function of the welding conditions. A maximum failure load of 2·8 kN was obtained in lap shear tests, compared with 2·9 kN for comparable AI-AI joints. The failure mode changed from interfacial debonding to nugget pullout and back to interfacial failure as the weld energy increased. A thin <2 μm reaction layer of FeAI₃ and Fe₂Al₅ formed at the interface with increasing weld energy. The factors determining the joint characteristics, interface reaction, and the microstructure evolution in the welds are discussed.     

Effect of calcium on the microstructure and mechanical properties of brazed joint using Ag–Cu–Zn brazing filler metal

The induction brazing of 316LN stainless steel using Ag–Cu–Zn filler metal containing various content of Ca was carried out to investigate the influence of impurity element Ca on the microstructure and mechanical properties of the brazed joint. The results showed that Ca additions caused the coarser of the grains and their irregular distribution. Increase of the Ca content resulted in the formations of brittle intermetallic compounds (IMCs) CaCu which perhaps lead to the formations of voids. All of the calcium-containing brazed joints performed better in microhardness than calcium-free ones and brazed joints containing 0.003 wt.% Ca showed the highest microhardness of 203HV. While the tensile strength decreased with the increment of Ca, from 460 MPa to 400 MPa. The combination effects of coarser grains, brittle IMCs and voids conduced to the reduction of tensile strength and microhardness of the brazed joints.     

Effect of Si content on microstructure and mechanical properties of Al–Si–Mg alloys

Microstructure and mechanical properties of as-cast and as-extruded Al–Si–Mg alloys with different Si content are investigated by tensile test, microstructure observation. High density of Si particles in the Al alloys can induce dynamic recrystallization during hot extrusion and it becomes more matured with an increase in the density of Si particles. The tensile strength of as-cast and as-extruded alloys can be improved with the increase of Si content and hot extrusion make the elongation of alloys increase dramatically. Considerable grain refining effect caused by recrystallization occurred during hot extrusion of S2 (equivalently commercial A356 alloy) and S3 (near eutectic alloy) alloys plays an important role in the improvement of elongation. A good combination of strength and elongation for the as-extruded S3 alloy indicates that near eutectic Al–Si alloys can be hot-extruded to produce aluminum profiles with high performance.