Alloy Side Research Articles

Effect of homogenization annealing on microstructure, composition and mechanical properties of 7050/6009 bimetal slab

Homogenization annealing of the 7050/6009 bimetal slab prepared by direct-chill casting was investigated and its effects on microstructural evolution, composition distribution and mechanical properties in the interfacial region of the bimetal were studied. The results show that the optimized homogenization annealing process was 460 °C for 24 h. After homogenization annealing, the Zn-rich phases and Al15(FeMn)3Si2 phases were precipitated at the interface of the bimetal. The diffusion layer thickness of homogenized bimetal increased by 30 µm from 440 to 480 °C for 24 h, while it increased by 280 µm from 12 to 36 h at 460 °C. The Vickers hardnesses at 6009 alloy side and interface of the bimetal decreased after homogenized annealing and grain coarsening was considered as the dominating softening mechanism. The hardness variation at 7050 alloy side was complicated due to the combined action of solution strengthening, dispersion strengthening and dissolution of reinforced phases.

Nd/YAG pulsed laser welding of TC4 titanium alloy to 301L stainless steel via pure copper interlayer

Pulsed laser welding of TC4 titanium alloy to SUS301L stainless steel with copper sheet as interlayer was studied in this paper. Microstructures of the joints were analyzed by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The mechanical properties of the joints were measured by nano-indentation test and tension test. Experimental results showed that copper interlayer was helping to decrease the Ti–Fe intermetallics by forming Cu solid solution, Cu2Ti, Cu–Ti, and Cu–Ti2 in the weld. The composition and microstructure in the weld were uneven, which led to an inhomogeneous distribution of the hardness. The average tensile strength of the joint was 350 MPa, and all the tensile samples fractured in the Cu–Ti2 layer with a maximum hardness in the weld adjacent to TC4 titanium alloy side.

Ultrasonic spot welding of magnesium alloy to titanium alloy

This research explores the joining between dissimilar alloys (magnesium alloy and titanium alloy) by ultrasonic spot welding. The tensile shear test shows that the joint strength increases with energy input. The fracture initiates inside magnesium alloy, indicating a high joining strength at the weld interface. Banded grain-refinement is found at the interface on the magnesium alloy side, neither transition layer nor inter-metallic compound layer is identified though. The interfacial temperature exceeds the temperature range for liquefying magnesium alloy. The precipitated aluminum from the liquid-phase magnesium alloy plays a bridging role in ultrasonic welding of magnesium alloy to titanium alloy.

Microstructure and mechanical properties of resistance-spot-welded joints for A5052 aluminum alloy and DP 600 steel

The microstructure and mechanical properties of resistance-spot-welded A5052 aluminum alloy and DP 600 dual-phase steel joint were studied. The fusion zone (FZ) and heat-affected zone (HAZ) of DP 600 exhibited lath martensite and ferrite-martensite structures, respectively. The microstructure of FZ and HAZ in the A5052 side was composed of cellular crystals and the boundary region of FZ exhibited a columnar crystal morphology. A Fe2Al5 intermetallic compound (IMC) layer with 3.3μm thickness was found adjacent to the DP 600 side, whereas a needle-shaped Fe4Al13 IMC layer with length of 0.67μm to 15.8μm was found adjacent to the aluminum alloy side. The maximum tensile shear load of the A5052/DP 600 joint was 5.5KN, with a corresponding molten nugget diameter of 6.3mm. The fracture morphology of the optimized A5052/DP 600 joint was mainly an elongated dimple fracture accompanied by cleavage fracture.

Corrosion Behavior and Strength of Dissimilar Bonding Material between Ti and Mg Alloys Fabricated by Spark Plasma Sintering.

Ti and solution treated Mg alloys such as AZ31B (ST), AZ61 (ST), AZ80 (ST) and AZ91 (ST) were successfully bonded at 475 °C by spark plasma sintering, which is a promising new method in welding field. The formation of Ti3Al intermetallic compound was found to be an important factor in controlling the bonding strength and galvanic corrosion resistance of dissimilar materials. The maximum bonding strength and bonding efficiency at 193 MPa and 96% were obtained from Ti/AZ91 (ST), in which a thick and uniform nano-level Ti3Al layer was observed. This sample also shows the highest galvanic corrosion resistance with a measured galvanic width and depth of 281 and 19 µm, respectively. The corrosion resistance of the matrix on Mg alloy side was controlled by its Al content. AZ91 (ST) exhibited the highest corrosion resistance considered from its corrode surface after corrosion test in Kroll’s etchant. The effect of Al content in Mg alloy on bonding strength and corrosion behavior of Ti/Mg alloy (ST) dissimilar materials is discussed in this work.

The interface microstructure and tensile properties of direct energy deposited TC11/Ti2AlNb dual alloy

Direct energy deposition process based on laser and powder feeding provides powerful ability in integrated manufacturing of multi-materials components. In this work, TC11/Ti2AlNb dual alloy thin walls were prepared by direct energy deposition process. The microstructure evolution and tensile properties of the dual alloy samples perpendicular to the interface after different heat treatments were investigated. The results indicated that there were two distinct composition transition zones between these two alloys due to the dilution effect during the process. From TC11 alloy side to Ti2AlNb alloy side, the phase evolved as: α+β→α+α2+β/B2+O→α2+β/B2+O→α2+B2+O. As-deposited materials presented better mechanical performance than other two counterparts both at room temperature and 650°C elevated temperature. For all samples, the fracture positions were not located within the interface zone, indicating the good mechanical performance of the interface zone. For demonstration, a TC11/Ti2AlNb dual alloy blisk was prepared by this process.

Microstructure and Properties of W–Cu Composite/Fe-Based Powder Alloy Vacuum Brazed Joint with Different Filler Metals

Abstract W–Cu composite and Fe-based powder alloy were brazed with filler metals of Ag–Cu and Cu–Mn–Co alloys in a vacuum furnace. Both of filler metals can join W–Cu composite with Fe-based powder alloy directly in the experiment process. Microstructure, distribution of elements and fracture morphology were observed and analyzed using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) methods, and phase composition of bonding area was analyzed by X-ray diffraction (XRD). The obtained results indicated that the smooth faying surface and dense microstructure of brazed joint were formed and the primary microstructure of brazing seam were, respectively, Ag(Cu) solid solution and Cu(Mn) solid solution, which ensured forming the stable connection of brazed joint. The bending strength of Ag-based and Cu-based brazed joint can, respectively, reach to 317 and 704 MPa, where fracture showed a typical ductile fracture characteristic. The fracture of Cu-based brazed joint located at brazing seam area, and the fracture of Ag-based brazed joint occurred in Fe-based powder alloy side.

Effect of Cr alloying interlayer on the interfacial bond strength of CuW/CuCr integral materials

The effects of Cr alloying interlayer on the microstructure and mechanical properties of the dissimilar CuW/CuCr joints prepared by sintering-infiltration method were studied. The hardness and electrical conductivity of the CuCr alloy side and the tensile strength of the CuW/CuCr integral materials were tested. The interfacial microstructure and fracture morphology of the CuW/CuCr joints were characterized by X-ray diffraction, optical microscopy, scanning electron microscope equipped with energy dispersive spectrometry. The results show that both the electrical conductivity and hardness of the CuCr alloy side of the aged CuW/CuCr joints are higher than those in the solid solution and infiltration condition. With increase of the Cr content, the regions of eutectic phase are expanded gradually on the CuCr alloy side, and the morphology of Cr particles changes from spot shape to rod-like shape. The highest interfacial bond strength can reach up to 446.66 MPa when Cu15 wt%Cr alloy is introduced into the interfacial region between CuW and CuCr alloy. The interfacial fracture morphology presents more cleavage fractures of W particles, and the Cu/W interphase has a good metallurgical bond.

Novel strip-cast Mg/Al clad sheets with excellent tensile and interfacial bonding properties.

In order to broaden industrial applications of Mg alloys, as lightest-weight metal alloys in practical uses, many efforts have been dedicated to manufacture various clad sheets which can complement inherent shortcomings of Mg alloys. Here, we present a new fabrication method of Mg/Al clad sheets by bonding thin Al alloy sheet on to Mg alloy melt during strip casting. In the as-strip-cast Mg/Al clad sheet, homogeneously distributed equi-axed dendrites existed in the Mg alloy side, and two types of thin reaction layers, i.e., γ (Mg17Al12) and β (Mg2Al3) phases, were formed along the Mg/Al interface. After post-treatments (homogenization, warm rolling, and annealing), the interfacial layers were deformed in a sawtooth shape by forming deformation bands in the Mg alloy and interfacial layers, which favorably led to dramatic improvement in tensile and interfacial bonding properties. This work presents new applications to multi-functional lightweight alloy sheets requiring excellent formability, surface quality, and corrosion resistance as well as tensile and interfacial bonding properties.

Investigation of the microstructure and properties of W75-Cu/W55-Cu brazed joint with Cu-Mn-Co filler metal

Abstract W75-Cu and W55-Cu alloys were brazed with a Cu-based filler metal under the process parameters of a brazing temperature of 1060°C and a holding time of 30 min in a vacuum furnace with a vacuum level >6×10-3 Pa. The microstructure, element distribution, phase constituents, four-point bending strength, and fracture morphology of the brazed joint were studied with a series of standard methods. The results indicated that the main microstructure of the brazing seam region was a Cu-based solid solution of Mn and Co dissolved in the Cu phase. The element Cu and a little element W from two sides of the base metals transited into the brazing seam region, and the elements Cu, Mn, and Co contained in the brazing filler metal diffused into the interface or even substrates. The main phases that existed in the brazed joint were Cu-rich phase Cu(Mn,Co), simple substance of W, simple substance of Cu, and trace amounts of Cu0.4W0.6. The four-point bending strength was about 950 MPa, and fracture occurred at the interface near the W75-Cu alloy side. The fracture morphology of the W75-Cu/W55-Cu brazed joint was identified as mixed ductile-brittle.

Characteristics evolution of 6009/7050 bimetal slab prepared by direct-chill casting process

6009/7050 alloy bimetal slab was prepared by a direct-chill (DC) casting process. Homogenizing annealing, hot rolling and T6 treatment were successively performed and their effects on microstructure and properties of the slab were studied. The results reveal that the average diffusion layer thickness of as-cast slab, determined by interdiffusion of elements Zn, Cu, Mg and Si, was about 400 µm. Excellent metallurgical bonding was achieved because all tensile samples fractured on the softer 6009 alloy side after homogenizing annealing. After homogenizing annealing plus rolling, the average diffusion layer thickness decreased to 100 µm, while the network structure of 7050 alloy side transformed to dispersive nubby structure. Furthermore, subsequent T6 treatment resulted in diffusion layer thickness up to 200 µm and an obvious increase of the Vickers hardness for both 7050 and 6009 sides. The layered structure of the as-cast 6009/7050 bimetal is retained after hot rolling and T6 treatment.

Effect of Sr addition on the characteristics of as-cast and rolled 3003/4004 clad aluminum

This paper examines the effects of Sr addition on the microstructure, compositon distribution and vickers hardness in the interfacial region of the as-cast and rolled 3003/4004 clad aluminum. The results reveal that the optimum adding amount of Sr on the as-cast Al-1.2Mn/Al10Si-xSr clad is 0.08 wt%. With Sr content increasing from 0 to 0.08 wt%, the average length and number of the primary α-Al phase growing from the diffusion layer significantly decreased and whose morphology appears in columar dendritic crystals, the celluar dendrite crystals, deep celluar crystals, fine celluar crystals and planar crystals, while the dendritic-crystal primary α-Al phase nucleating and growing from inner AlSi alloy side also show obvious decease in secondary dendrite spacing; meanwhile, eutectic Si phases were gradually modified from coarse plates, coralloid-plates mixed structure to fine branchy coralloid structure in three-dimensional morphology. After rolling, the diffusion layer thickness of the Al-1.2Mn/Al10Si0.08Sr clad is decreased by 66.7%, compared to that of unmodified clad alloy. This decreased diffusion layer thickness may be determined by augmented plastic strain and restraining diffusion of Si atoms in diffusion layer. Morever, average vickers hardness on interface and AlSi side of the Al-1.2Mn/Al10Si0.08Sr clad showed slight increase and more uniform distribution than that of unmodified clad alloy. This uniform distribution and improved hardness primarily attribute to presence of fine branchy coralloid silicon phase and its stronger dispersion strengthening as well as solution strengthening caused by interdiffusion of Si, Mn and Sr elements.

Effect of explosive mixture on quality of explosive welds of copper to aluminium

The aim of this research is to investigate the influence of explosive ratio and type of sensitizer on the quality of explosive welds between copper and aluminium alloy plates. The welds were performed on a partially overlapping joint configuration using an emulsion explosive (EE) with two different sensitizers, hollow glass microspheres (HGMS) and expanded polystyrene spheres (EPS). Welds with an improved surface were achieved by using the HGMS sensitizer. A higher wave amplitude was registered in welds produced with the EPS sensitizer. In turn, the dimension of the molten pockets was influenced by the explosive ratio, increasing in size with increases in the values of this parameter. The intermetallic content of these zones varied according to the sensitizer type. Unlike the CuAl2 phase, the Cu-richer phases CuAl and Cu9Al4 were only identified in welds performed using the EPS sensitizer. An increase in hardness was observed at the interface of all welds, which resulted from both the presence of intermetallic phases and the plastic deformation of the materials promoted by the impact. This effect was most evident on the aluminium alloy side. All the welds had a greater strength than copper, i.e. the weakest material of the joint.

Refilled friction stir spot welding of aluminum alloy to galvanized steel sheets

Dissimilar materials lap joining of aluminum alloy to galvanized steel sheets was investigated with refilled friction stir spot welding (Refilled FSSW). For the lap joint between 1.0mm thick Novelist AC 170 PX aluminum alloy and 1.2mm thick ST06 Z galvanized steel sheets, the maximum tensile/shear fracture load is 3044N with cross-tension fracture load of 296N. For that between 1.5mm thick Aleris Superlite 200 ST aluminum alloy and 1.2mm thick ST06 Z galvanized steel sheets, the maximum tensile/shear fracture load reaches 4500N and the maximum cross-tension fracture load is 359N. All samples failed through the Al/steel interface during tensile/shear and cross-tension tests. The microstructure, composition, fractogragh and fracture mode of Al/steel joints were analyzed with electron probe microanalysis (EPMA), scanning electron microscope (SEM) and X-ray diffraction (XRD). Zinc and oxygen rich layer were observed in the interface on aluminum alloy side, and ZnO phase was detected on the fractured surface of both aluminum alloy and steel sides. The samples during tensile/shear test failed mainly through shear brittle fracture with features of cleavage and intergranular fracture feature. The spot weld can be distinguished as pin-refilled zone and sleeve-plunging zone due to the distribution of zinc coating.

Interfacial analysis of porcelain fused to high-palladium alloy with different observation methods

Background/purposeIn a previous fractural study of implant-supported crowns, it was found that the palladium−silver crowns possessed the highest fracture force. The ceramic–metal interface was examined to explain its high resistance to fracture. Materials and methodsPalladium−silver crowns with the morphology of a maxillary second premolar were prepared following standard dental laboratory procedures. Crown specimens were compressed vertically in the center of the occlusal surface until fracture, using a universal testing machine. The fractured surfaces were examined using scanning electron microscopy combined with energy dispersive X-ray spectroscopy to determine the failure mode. The ceramic–metal interface of the crown was examined with electron probe microanalysis. Additionally, sheet specimens with a dimension of 10 × 9 × 4 mm3 were prepared to examine the surface morphology and composition of palladium−silver alloy after oxidation and porcelain-fused-to-metal firing cycles. ResultsThe average fracture force was 1425 ± 392N. Analyses with scanning electron microscopy combined with energy dispersive X-ray spectroscopy revealed that the failure mode was cohesive within the ceramic layer. Electron probe microanalysis micrographs indicated that Sn and In were found to distribute only on the alloy side of the ceramometal crown. Energy dispersive X-ray spectroscopy analysis and electron probe microanalysis micrographs confirmed that ZnO had diffused into the ceramic phase. ConclusionIn2O3, SnO2, and ZnO were found along the interface; the presence of these oxides at the boundary promotes ceramic–metal adhesion, and this resulted in cohesive failure of the ceramic layer. ZnO was found to diffuse into the ceramic phase, and it is suggested to be beneficial for high fracture resistance in the present study.

Processing and Optimization of Dissimilar Friction Stir Welding of AA 2219 and AA 7039 Alloys

The present paper discusses the optimization of dissimilar friction stir welding of AA 2219 and AA 7039 alloys with respect to tool design issues including microstructural study of weld. The optimized ultimate tensile strength was ~280 MPa, and % elongation was ~11.5. It was observed that the extent of tool shoulder flat surface and tool rotational speed influenced the weld quality significantly. A mathematical model was also developed using response surface regression analysis to predict the effects of tool geometry and process variables on dissimilar AA 2219 and AA 7039 alloys welds. The microstructure evolution and mechanical properties were investigated by employing electron backscatter diffraction technique, Vickers microhardness, and tensile testing, respectively. The microstructural observations indicated that the grain size obtained at advancing side (AA 2219 alloy side) was much finer compared to the retreating side (AA 7039 alloy side). Hardness distribution in the stir zone was inhomogeneous, which might be due to inadequate mixing of weld zone material. The hardness values observed at the weld zone were lower than that in the base materials.

Joining of AZ31 and AZ91 Mg alloys by friction stir welding

Abstract Two dissimilar magnesium (Mg) alloy sheets, one with low aluminium (AZ31) and another with high aluminium (AZ91) content, were successfully joined by friction stir welding (FSW). The effect of process parameters on the formation of hot cracks was investigated. A sound metallurgical joint was obtained at optimized process parameters (1400 rpm with 25 mm/min feed) which contained fine grains and distributed β (Mg17Al12) phase within the nugget zone. An increasing trend in the hardness measurements has also confirmed more amount of dissolution of aluminium within the nugget zone. A sharp interface between nugget zone and thermo mechanical affected zone (TMAZ) was clearly noticed at the AZ31 Mg alloy side (advancing) but not on the AZ91 Mg alloy side (retreating). From the results it can be concluded that FSW can be effectively used to join dissimilar metals, particularly difficult to process metals such as Mg alloys, and hot cracking can be completely eliminated by choosing appropriate process parameters to achieve sound joint.

Effects of preheat treatment on microstructure evolution and properties of brazed-fusion welded joint of aluminum alloy to steel

Microstructure and mechanical properties of brazed-fusion welded joint of aluminum alloy to galvanized steel were studied by analyzing and comparing the as-welded state and that with preheat treatment at different temperatures. The preheat treatment process not only increased the spreadability of weld seam and thickness of intermetallic compound (IMC) layer at brazed interface but also changed phase composition of IMC layer. In as-welded joint, there were two IMC layers (layer I included θ-Fe4Al13 and τ5-Al8Fe2Si adjacent to weld seam, and layer II was composed of η-Fe2Al5 near the steel side), while a newly formed nanoscale Fe-rich layer III which might consist of FeAl and Fe3Al was found in the joint with preheat treatment, causing by interdiffusion between layer II and Fe at high temperature. Incomplete brazing at weld root deteriorated the strength of as-welded joint. The joint with preheat treatment at 100°C, fractured at heat-affected zone on aluminum alloy side, exhibited the highest strength which reached nearly 80% of that of aluminum alloy. The thicker IMC layer at weld root led to the fracture at brazed interface when preheat treatment at 200°C.

Simulation Study of Al-1Mn/Al-10Si Circular Clad Ingots Prepared by Direct Chill Casting

A modified direct chill casting process based on Novelis FusionTM Technology co-casting process was used recently to prepare Al-1Mn/Al-10Si circular clad ingots. In the current study, a comprehensive simulation model was developed to investigate the direct chill casting process for preparing the Al-1Mn/Al-10Si circular clad ingots, and a parametric study and experimental research of the direct chill casting process was conducted to explore potential success and failure casting conditions. The simulation results revealed the bonding mechanism of the Al-1Mn/Al-10Si interface in the direct chill casting process and identified the effect of certain parameters on casting performance. The results indicated that the effect of casting speed and Al-1Mn casting temperature on the variations of the minimum solid fraction of Al-1Mn at the interface is stronger than that of cooling water flow rate in inner mold, while Al-10Si casting temperature is the weakest of the four casting parameters. The corresponding experimental results verified that Al-1Mn/Al-10Si circular clad ingot with acceptable metallurgical bonding can be successfully prepared by direct chill casting process under the proper casting parameters. The thickness of diffusion zone is about 40 μm, and the fractured position in tensile test was located in the Al-1Mn alloy side which indicated the strength of the interfacial region is higher than that of Al-1Mn alloy.

Analysis of material flow in the sheet forming of friction-stir welds on alloys of mild steel and aluminum

The deep drawability of and material flow in friction-stir welds of dissimilar steel/aluminum were investigated in this study. Steel/Al tailor-welded blanks (TWBs) were found to possess sufficient joint strength and deep drawability with limiting drawing ratios (LDRs) as low as 1.7. However, the drawability of these TWBs was lower than that of the two base materials. Fracturing was observed near the weld line on the flat bottom of the aluminum alloy side. In addition, the aluminum alloy near the fractured area in the TWB cup was subjected to significant strain near the forming limit, correlating to a significant loss in their deep drawability. Numerical simulation results indicated that slightly enhancing the friction coefficient between the punch and the blank significantly mitigated the significant strain near the fracture area. Deep drawing tests verified that the LDRs of TWBs obtained using rosin were increased by nearly 19% compared with that obtained using conventional press oil. Therefore, this approach of enhancing the friction coefficient can be effectively applied to improve the formability of dissimilar steel/aluminum TWBs.