Microstructure Analysis and Mechanical Performance of TA10/6061 Large Size Explosive Welding Composite Pipes Based on Numerical Simulation Verification

Zhou H., Shao F., Bai L., Yuan J., Xu Q., Liu H.

Jandaghi M., Pouraliakbar H., Moverare J., Fallah V., Khalaj G.

Wang P., Zhao S., Nai X., Chen H., Wang P., Song X., Li W.

The microstructure evolution and mechanical properties of Ti2AlNb/Ti-36.5Zr–10Ni–15Cu-0.5Co-0.5Nb/Ti60 brazed joints before and after homogenization treatment were comprehensively evaluated. Initially, the joints brazed at 900 °C for 15 min exhibited a continuous coarse strip network of Ti2Cu, Ti2Ni, Zr2Cu and Zr2Ni brittle intermetallic compounds in the central region of the braze seam, which detrimentally affecting the mechanical properties. Subsequent homogenization at 600 °C for 1 h, the amount of continuous brittle intermetallic compounds significantly decreased through sufficient atomic diffusion. Concurrently, the inadequately transformed eutectic β-Ti within the intermetallic compounds underwent an active eutectoid reaction. This structural transformation established a coherent interface with elastic distortion between the α-Ti and intermetallic compounds, effectively minimizing the lattice mismatch. Thus, a widmanstatten structure (i.e., acicular intermetallic compounds within a eutectoid microstructure matrix) with improved mechanical properties was formed. Consequently, a mean shear strength of 350.3 MPa was attained after treatment at 600 °C for 1 h, marking a substantial 206 % increase compared to that before homogenization treatment. This finding underlines the pivotal role of homogenization treatment in optimizing the performance of aeroengine components.

Li B., Zhang M., Zhang K., Kan C., Zhang X.

The nucleation and growth of fine austenitic grain at interface of L415QS/N08825 bimetallic composite pipe achieved by explosive welding is systematically studied. Results show that the L415QS/N08825 interface have heat affected zone (HAZ) that is similar with GH2132 superalloy (Fe-25Ni-15Cr). Two kinds of austenitic grains: columnar grains and ultra-fine equiaxed grain with large angle grain boundaries were identified at HAZ that nucleated from both L415QS and N08825 base alloy in the melts zone, and the growth of the nucleus is based on the size of melts zone. Room temperature nanoindetation test revealed that these fine equiaxed and columnar austenitic grains exhibit enhanced hardness compared with those of the base metals.

Yuan J., Shao F., Bai L., Zhang H., Xu Q., Gao L., Xie X., Pan Y.

In this work, the interface morphology and element distribution of the TC1/AA1060/AA6061 composite plate were studied. The grain information was investigated by electron backscattered diffraction and interface temperature was obtained by numerical simulation to explain the grain information. The experimental samples were tested by mechanical methods. The results show that the TC1/AA1060/AA6061 composite plate has better welding quality by observing interface morphology and testing mechanical properties. The morphology of the two interfaces was consistent with the simulation results, and the interface temperature can be explained by the grain information at interfaces and vortex regions. The diffusion width of elements at the TC1/AA1060 interface was 12.3 µm and no intermetallic compounds were detected; Only Al and O element were detected in two vortex regions. In addition, nanoindentation test was performed at different regions and the results were discussed.

LONG J., ZHANG L., ZHU L., ZHANG L., WU J., ZHUANG M.

The low-cycle fatigue properties of 30 mm Ti6Al4V titanium alloy joints welded by vacuum electron beam welding and laser wobble welding with filler wire were compared. The test results show that the low-cycle fatigue performance of the electron beam welding joint is close to that of the base meal, while the low-cycle fatigue performance of the laser wobble welding with a filler wire joint is clearly inferior to that of the electron beam welding joint and base meal. An examination of the microhardness of the base metal, heat-affected zones and weld area of the two joints found that the microhardness of the weld area of the electron beam welding joint is close to that of the base meal, but is lower than that of the heat-affected zones on both sides. The weld area of the laser wobble welding with the filler wire joint is significantly weakened.

Xia Z., Wang H., Shi C., Sun Z., Wang Q., Luo X.

The titanium/aluminum composite materials overcome the limitations of single metal materials and achieve lightweight, high-strength, and corrosion-resistant properties. However, there have been no reports on explosion-welded composites of titanium alloys and seven-series aluminum alloys. Therefore, TA1/Al1060/Al7075 explosion-welded plates with three different explosive thicknesses were successfully prepared using Al1060 as the transition layer. The SPH-FEM coupled algorithm was employed to analyze the detonation process in detail and predict the interface under different explosive thicknesses. The results showed that during the explosion welding process, the high temperature, pressure, and high-speed impact resulted in significant plastic deformation and jetting phenomena at the bonding interface, which were in good agreement with the experimental observations. With the increase in explosive thickness, the TA1/Al1060 bonding interface exhibited a flat shape, while the Al1060/Al7075 interface transitioned from a flat to a wavy morphology. Moreover, the crack, vortex, and TiAl3 were observed at the interface. Mechanical testing results revealed that the composite plate with a 35 mm explosive thickness exhibited the best tensile, shear, and bending performance, indicating the optimal process parameter. This study provides significant support and reference for the application of explosion welding technology in titanium alloys and seven-series aluminum alloy composite materials.

Zhang B., Wan Z.

Titanium alloys has high fatigue resistance, high corrosion resistance, high temperature resistance, and other excellent properties, and have been widely used in deep-sea equipment and aviation industries. In this paper, the fracture mechanism and failure strain of TA31 titanium alloy, which has been widely used in deep-sea equipment, were studied experimentally and numerically in different stress states. Considering the pressure sensitivity, the Modified Johnson-Cook (MJC) model and the Bonora damage model were used to study the fracture behavior. In order to obtain the parameters of models, four types of specimens under different stress triaxiality were conducted, and a hybrid experimental-numerical approach was employed in this paper. Then, the coupled constitutive elastic–plastic-damage model was developed and implemented in ABAQUS explicit finite element analysis (FEA) code. Finally, to validate the suggested model, FEA simulation was carried out and compared with the experimental results. The comparison revealed that the Bonora model with constant parameters was not enough to predict the failure strain. The damage parameters were sensitive to the stress triaxiality. In addition, the fracture morphology was observed by scanning electron microscope (SEM), which revealed the micro-mechanism of failure for TA31 titanium alloy. It is concluded that a higher stress triaxiality and shear mechanism lead to lower plastic deformation, and will inhibit the void growth on the damage evolution.

Zhu L., Pan Y., Liu Y., Sun Z., Wang X., Nan H., Mughal M., Lu D., Lu X.

Powder hot isostatic pressing (HIP) is an effective method to achieve near-net-shape manufacturing of high-quality complex thin-walled titanium alloy parts, and it has received extensive attention in recent years. However, there are few reports about the microstructure characteristics on the strengthening and toughening mechanisms of powder hot isostatic pressed (HIPed) titanium alloys. Therefore, TA15 powder was prepared into alloy by HIP approach, which was used to explore the microstructure characteristics at different HIP temperatures and the corresponding tensile properties and fracture toughness. Results show that the fabricated alloy has a “basket-like structure” when the HIP temperature is below 950°C, consisting of lath clusters and surrounding small equiaxed grains belts. When the HIP temperature is higher than 950°C, the microstructure gradually transforms into the Widmanstatten structure, accompanied by a significant increase in grain size. The tensile strength and elongation are reduced from 948 MPa and 17.3% for the 910°C specimen to 861 MPa and 10% for the 970°C specimen. The corresponding tensile fracture mode changes from transcrystalline plastic fracture to mixed fracture including intercrystalline cleavage. The fracture toughness of the specimens increases from 82.64 MPa·m1/2 for the 910°C specimen to 140.18 MPa·m1/2 for the 970°C specimen. Specimens below 950°C tend to form holes due to the prior particle boundaries (PPBs), which is not conducive to toughening. Specimens above 950°C have high fracture toughness due to the crack deflection, crack branching, and shear plastic deformation of the Widmanstatten structure. This study provides a valid reference for the development of powder HIPed titanium alloy.

Wu X., Shi C., Feng K., Gao L., Li W., Qian K.

Abstract The welding parameters of TA2/1060/5083 were calculated accurately through a combination of explosive welding weldability window and numerical simulation, based on which explosion welding experiments were conducted using these parameters obtained. Then, a test was carried out on the mechanical properties of the composite plates obtained from the experiments and microstructure characterization was performed. As suggested by the results, TA2/1060 was a excellent straight bond, and the interface of 1060/5083 was a sine-wave featuring both vortex structure and splashing molten block structure, with an average wavelength of 700 μm and a wave height of 100 μm. The tensile strength and shear strength of the composite materials reached 354 MPa and 110 MPa, respectively, while the material showed the signs of ductile fracture. Moreover, work hardening and fine grain strengthening occurred at the interface, as did the element diffusion of Ti-Al, with a maximum diffusion depth of 32 μm.

Zhang T., Wang W., Yan Z., Zhang J.

Interfacial structure greatly affects the mechanical properties of laminated plates. However, the critical material properties that impact the interfacial morphology, appearance, and associated bonding mechanism of explosive welded plates are still unknown. In this paper, the same base plate (AZ31B alloy) and different flyer metals (aluminum alloy, copper, and stainless steel) were used to investigate interfacial morphology and structure. SEM and TEM results showed that typical sine wave, wave-like, and half-wave-like interfaces were found at the bonding interfaces of Al/Mg, Cu/Mg and SS/Mg clad plates, respectively. The different interfacial morphologies were mainly due to the differences in hardness and yield strength between the flyer and base metals. The results of the microstructural distribution at the bonding interface indicated metallurgical bonding, instead of the commonly believed solid-state bonding, in the explosive welded clad plate. In addition, the shear strength of the bonding interface of the explosive welded Al/Mg, Cu/Mg and SS/Mg clad plates can reach up to 201.2 MPa, 147.8 MPa, and 128.4 MPa, respectively. The proposed research provides the design basis for laminated composite metal plates fabrication by explosive welding technology.

Wu X., Shi C., Fang Z., Lin S., Sun Z.

In order to obtain titanium and aluminum composites with excellent performance and master the energy flow form when interlayer is used in explosive welding technology, energy calculation, SPH numerical simulation and experiment were used to conduct a comparative study of TA2/5083 and TA2/1060/5083 in this paper. Under the experiment conditions, TA2/1060, 1060/5083, TA2/5083 interface welding energy are respectively 547.17 MJ, 1178.86 MJ and 1455.5 MJ.The use of 1060 interlayer improves energy utilization efficiency by 14%. Numerical simulations and experiments showed that there was a continuous melting zone and a non-welded zone at the interface without interlayer. After the interlayer was used, the TA2/1060 interface was flat and the 1060/5083 interface showed a wave. There was no brittle intermetallic compound at the titanium‑aluminum composite interface. The use of interlayer reduces the welding energy of a single interface, and the constructed theoretical equation showed that the interface energy can be accurately designed by adjusting parameters of explosives, flyer plates, interlayers and base plates. The use of pure aluminum interlayer is an effective means to improve titanium‑aluminum explosive welding conditions • A direct calculation formula for the welding energy of explosive welding interface is constructed. • The use of interlayers to redistribute energy will definitely increase the energy utilization efficiency in any material，experiments improved by 14%. • The prepared TA2/1060/5083 interface elements exist in the form of titanium‑aluminum solid solution, and there is no continuous melting zone. • Pure aluminum can be used for explosive welding to prepare titanium alloy‑magnesium aluminum alloy composite materials.

Sun Z., Shi C., Shi H., Li F., Gao L., Wang G.

Different from the traditional parallel method, double vertical explosive welding adopts a closed charge structure, and two composite plates are formed by one explosion. The energy distribution and interface morphology in the parallel methods and double methods were studied by numerical simulation and experiments. The theory of “energy flow in stages during explosive welding” was first proposed and energy balances at the start and end welding were obtained in this paper. The temporal and spatial distribution of the relevant parameters was analyzed. The value and proportion of each energy were calculated in sections by numerical simulation. The results showed that the detonation products in double method had higher internal energy and lower kinetic energy. The collision velocity obtained by the two methods was close. The kinetic energy of the flyer plate, plastic deformation energy and jet energy in the double method were about twice those in the parallel method. The experimental results showed that the dimension of the interface waves in two methods was close, but more melted microstructures were observed in the double method, whose compositions were mainly TiFe2 and TiFe3. Double vertical explosive welding improved energy efficiency and saved at least half of the explosives.

Ma Q., Shao F., Bai L., Xu Q., Xie X., Shen M.

The corrosion fatigue properties and fracture characteristics of friction stir welding joints of 7075 aluminum alloys were studied via corrosion fatigue tests, electrochemical measurements, and corrosion fatigue morphology and microstructure observations. The results show that the corrosion fatigue crack of the friction stir welding (FSW) joint of 7075 aluminum alloys originated in the junction zone between the thermomechanically affected zone and the weld nugget zone. The corrosion fatigue life of the joint decreased with increasing stress amplitude, with an S–N curve equation of lgN = 5.845 − 0.014S. Multiple crack sources were observed in the corrosion fatigue fracture. The main crack source originated from the corrosion pits at the interface between the thermomechanically affected zone and the weld nugget zone due to the influence of the coarse microstructure and the large potential difference between both zones. Corrosion morphologies of a rock candy block and an ant nest appeared in the crack propagation zone and the grain boundary of the weld nugget zone. In addition, fatigue speckles and intergranular fractures were observed, as well as brittle fracture characterized by cleavage steps and secondary cracks in the final fracture zone.

Carvalho G.H., Galvão I., Mendes R., Leal R.M., Loureiro A.

This work aimed to study aluminium to stainless steel explosive welds produced using two different interlayers: carbon steel and niobium. The use of each interlayer was analysed and compared microstructurally and mechanically using many characterisation techniques. The final joints using both interlayers presented favourable interfacial microstructure: waves on both interfaces. However, the joint using the carbon steel interlayer showed the best mechanical properties compared to the joints using the niobium interlayer. All interfaces found on both welds were wavy. However, depending on the metallic alloy combination, the shape of the wave is completely different. The results suggest that the shape of the waves is influenced by the shock impedance mismatch of the materials being welded. The impedance mismatch parameter (IMP) developed for explosive welding in this work proved to be a compelling method to order metallic combinations in a single axis to estimate the tendency to form typical or curled waves. Typical symmetrical waves tend to develop less quantity of IMCs than curled waves. However, the mechanical tests performed did not detect differences that could have been caused by this difference.