Papers by Keyword: Dissimilar Joint

Abstract: In order to evaluate the corrosion fatigue property of dissimilar joint by the simultaneous fatigue-corrosion test, an original compact shear fatigue test machine has been developed and installed in the combined cycle corrosion equipment. The material used were an innovative ultra-high strength steel (i-UHSS) with the ultimate strength of 1.5 GPa & large elongation of 20 % and an innovative Al-Mg alloy with high ductility. The dissimilar lap joints were fabricated by resistance spot welding (RSW) or refill friction stir spot welding (RFSSW). An innovative adhesive was also employed for producing the weld-bonded (WB) joints. An accelerated corrosion condition conducted in this research was the climate of high temperature & high humidity. The natural corrosion fatigue tests were also performed outdoor on Miyakojima Island in Japan and indoor in an air-conditioned room. The accelerated corrosion fatigue tests suggest that the corrosion fatigue property of the dissimilar WB joint joined by RSW seems to be better than that of the WB joint joined by RFSSW because of the difference in the area of adhesive interface. In addition, it is considered that the crack would propagate in the adhesive interface and then lap joint might break suddenly after achieving the crack to the circumference of joint interface produced by RSW or RFSSW. Moreover, it can be concluded that the accelerated corrosion condition employed in the research seems to be an appropriate condition for examining the corrosion fatigue property of lap joint in the climate of high temperature and high humidity.

Abstract: Industrial requirements to establish metallic joints between dissimilar metals in the electric area. The ultrasonic welding process is an optimal process to joint thin sheets or foils. The goal of the research was to optimize the ultrasonic welding parameters to join thin nickel-coated copper sheets and aluminium sheets. It used a 0.5 mm thick high-purity copper (Cu-OF-R200) sheet coated with a 10 μm pure nickel layer and a 0.5 mm thick aluminium (1050A H24) sheet. The ultrasonic welding is made by a Branson Ultraweld L20 ultrasonic welder equipment. The mechanical properties and exacting geometrical tolerance of the joint were required. The welding parameter optimization is made empirically, with several welding tests. The optimal welding parameters were confirmed by non-destructive and destructive tests of the joints. The non-destructive tests were the visual inspection and geometrical measurements of the joint sizes. The destructive tests were tensile tests and macroscopic and microscopic tests. The completed test results confirmed the process applicability and the quality of the joint.

Abstract: As a result of R&D efforts about the advanced materials, an ultra-high strength steel (UHHS) and a carbon fiber reinforced thermos-plastic (CFRTP) have been developed. In this study, various advanced multi-material dissimilar lap joints using UHHS, CFRTP and an aluminum alloy of A5083P-O were fabricated by the resistance spot welding (RSW), refill friction stir spot welding (RFSSW), friction stir spot welding (FSSW) and laser irradiation assistance plastic welding (LIAPW). Where, the total heat input for each joining method was varied in order to examine the influence of welding condition on joint performances, which were the tensile shear strength, shear fatigue property and corrosion shear fatigue property. The tensile shear strength of UHHS and A5083P-O joined by RFSSW is almost two times of that produced by RSW, and this difference seems to be mainly caused by the difference of joint area. The difference of joint area also affects the tensile shear strength of UHHS & CFRTP or A5083P-O &CFRTP lap joints made by FSSW and LIAPW, and the joint strength of LIAPW is larger than that of FSSW. As for the shear fatigue tests, it is found that the fatigue strength seems to decrease almost monotonically with increasing the applied load regardless of the types of dissimilar materials. Moreover, through the corrosion shear fatigue tests for A5083P-O and CFRTP joined by FSSW or LIAPW, it is found that the corrosion fatigue property seems to be controlled by the crack propagation behavior.

Abstract: In this paper, the effect of rotary friction welding on hardness and microstructures of weld zones and base metal zones of Ti-6Al-4V and Cu have been investigated. A rotary friction welding technique was used to perform dissimilar joining of Cu and Ti-6Al-4V bars. Friction welding process parameters were optimized process parameters of a 5-ton rotary friction welding machine. The upset pressures were applied from 30 kg/mm^2, 40 kg/mm² and 50 kg/mm². The dissimilar joint was successfully formed at upset pressure of 50 kg/mm². The friction welded joints were failed in drop test after welding at the lower upset pressures (30 kg/mm² and 40 kg/mm²).The hardness and microstructures were characterized for weld joint formed at 50 kg/mm². The weld zone, base metal and weld interface and base metals were analysed to understand microstructures and elemental diffusion of Ti and Cu. The welded specimens were examined by using an optical microscope and scanning electron microscope. Grain refinement was seen in Cu near the interface of the joint whereas in the case of titanium circular patterns of grains were seen near the interface of the joint. The micro hardness of Ti-6Al-4V was increased from 307 HV to 365 HV and for Cu increased from 240 HV to 290 HV. Intermetallic compounds such TiCu₄ and Ti₂Cu were found at weld zone by X-ray diffraction analysis.

Abstract: The purpose of this research was to study the diffuse element and mechanical property of Semi-solid casting (SSC) 7075 and 6061 Al alloy from diffusion welding (DW). The results found that Zn elements were successfully diffused. Mg₂Si and MgZn₂ intermetallics were precipitated from plate-like shape to flake shape. The high bonding temperature and bonding time caused diffuse elements distributed throughout the material. The mechanical property showed that the maximium average tensile strength was 76.80 MPa from bonding temperature at 723 K and 120 min bonding time. The hardness in bonded line was around 63 HV to74 HV.

Abstract: In order to weld dissimilar materials with dramatically different properties such as aluminum and steel, friction stir welding (FSW) offers many advantages over conventional fusion welding techniques. However, producing strong and durable FSW joints requires full characterization of these joints including metallurgical and mechanical characterization. In this work, many process parameters and two different tools are put to test and the resulting FSW joints are characterized. Their mechanical strength is investigated in tension with respect to intermetallic compounds content analyzed using SEM coupled to EDX. The soundest 2mm thick joints recovered 55% of the strength of the original un-welded metal whereas in the case of the 3mm thick joints 47% of the strength could only be recovered in the best case. It was revealed that as the content in intermetallic compound increases the strength of the joints decreases. Additionally, it was found that the higher the mechanical deformation, the more these compounds are abundant; in other words, intermetallic compounds were largely found in the middle and bottom sections of the 3mm thick samples which is where the threads of the pin do most of their work. The compositions of these intermetallic phases along the abutting surfaces is also proposed based on the elemental composition of Fe and Al as detected by the scanning electron microscopy.

Abstract: The influence of different thickness combinations was investigated on the strength of the lap joint of dissimilar steels. In this study, lap joints of dissimilar steels were welded by laser welding. The tensile shear test was conducted for the lap joints. Rotational deformation process around the weld bead of the lap joint was observed by a digital video camera during the test. Motion analysis from the video of the tensile shear test indicated that the rotation angle around the weld bead was reduced by overlapping higher strength grade steel. Three-dimensional elastic-plastic finite element analysis was performed for the tensile shear test of the lap joint. The numerically calculated deformation behavior of the lap joint subjected to tensile shear loading showed reasonable agreement with the experimental record. It was found that the rotation angle was reduced and tensile shear strength of the lap joint increase by overlapping higher strength grade steel sheet.

Abstract: Friction stir welding (FSW) is one of the solid-state welding and it has been widely employed for joining aluminum alloys. In addition, as a result of R&D efforts about FSW tool, this method is expected to join the steels and/or various dissimilar materials. In order to examine the thermal and mechanical behavior in FSW, many numerical studies have been conducted and the heat generation behavior near FSW tool is precisely demonstrated by using the moving particle semi-implicit (MPS) method which is one of the particle method. In this research, in order to reduce the computational time, a new parcel method based on MPS is developed and its applicability is examined for simulating the friction stir welded dissimilar joint between V-ally and austenite stainless steel SUS316L. From the serial computational results, it is revealed that the influence of rotational speed on the heat generation during FSW seems to be larger than that of traveling speed. Moreover, the numerical result indicates that the sound dissimilar joint might be fabricated when V-alloy is set to be the retreating side (RS), the FSW tool is inserted in RS and the rotational speed increased appropriately although the two materials have not been joined in this welding condition of FSW experimentally.

Abstract: Ultrasonic welding is a suitable solid-state joining technique for producing high strength joints of similar or dissimilar materials, even of material combinations that were previously considered as not weldable. Several varieties of transmitting the ultrasound into the joining partners exist whereas the investigated torsional welding principle utilizes a ring shaped sonotrode for transmitting ultrasonic vibrations tangentially to the welding force into the workpiece. Due to the specific sonotrode geometry ultrasonic torsional welding is a remarkably gentle welding technique, allowing to join even most sensitive components e.g. sensors or brittle elements. Nevertheless, ultrasonic torsional welded joints show high tensile strengths and helium-tightness. Current investigations focus on the realization of metal/glass ceramics joints. In this project two metals with different thermal expansion coefficients have been utilized as the metal joining partner. The glass joining partner was the commercially available Li₂O-Al₂O₃-SiO₂ CERAN. For examining the microstructure light as well as scanning electron microscopy have been performed. Additionally, mechanical characterization has been carried out through tensile shear tests.

Abstract: The dissimilar weld joint of HR3C steel and T92 steel is widely used in the ultra supercritical (USC) boiler due to the different service conditions of HR3C steel and T92 steel. It is important to study how serviced influenced the HR3C/T92 dissimilar joint. The HR3C/T92 dissimilar joint had already served 51020 h under 605 °C and 26.25 MPa. The microstructure and mechanical properties of the long term serviced HR3C/T92 dissimilar joint were tested by XRD, SEM, EPMA,TEM, the impact testing machine and the creep and stress rupture testing machine. The XRD results show that the weld is mainly γ-Fe, which is similar to the HR3C base metal, while the T92 base metal is mainly α-Fe. The SEM results indicate that serviced HR3C’s precipitation behavior is complicated, cause multiple precipitated phases precipitated during the service. Chain-liked M₂₃C₆ precipitated along the grain boundary. M₂₃C₆ phase cause the chromium depletion zone along the grain boundary. T92 base metal precipitated lots of carbide particles during the service. Those carbide particles are around 1 μm. The impact fracture of HR3C base metal is brittle fracture while the impact fracture of T92 base metal is ductile fracture. Moreover, the impact fracture of weld is mixed fracture. Chain-liked M₂₃C₆ along the grain boundary is the main cause of the brittleness of serviced HR3C steel.The constant strain creep tests were proceeded under 650 °C, 700 °C and 750 °C. The high-temperature creep resistance of HR3C base metal is better than that of T92 base metal after service. The resistant to high-temperature creep of served joint is similar to that of serviced T92 base metal. With the increase of temperature, the creep resistance of the T92 base metal decreases the most. On the contrary, the creep resistance of the HR3C base metal shows the minimum reduction.