Effects of a constricted nozzle on the arc phenomena in Tungsten Inert Gas (TIG) welding process are investigated by numerical simulation. The obtained results show that the temperature and velocity of the arc plasma are increased by attaching an additional gas nozzle which is called "constricted nozzle". As a result, the iron vapor does not diffused upward but transported outward. In addition, the heat transfer to the base metal surface is enhanced.
Much attention has been paid to FSW as a useful joining process that provides superior characteristics compared with conventional fusion welding. However, the FSW equipment must have a high stiffness due to the applied load and the tool torque, which increases the size of the equipment. Therefore, it is difficult to use the FSW technique on-site for repairs and/or hand-operated welding. In this study, the relationship between the FSW parameters and the process loads was investigated for the FSW with a counterbalanced tool and preheating to evaluate the possible miniaturization of the equipment. The results revealed that the counterbalanced tool concept with preheating was effective for the miniaturization of the equipment because it reduces the applied load and the tool torque during the FSW. Welding direction force Fx and transverse direction force Fy can be reduced below 70N and 50N, respectively.
Flip chip technology with Au bumps on a substrate has been widely applied to electronic equipment such as smartphone. The purposes of this study are to examine the effect of Al pad thickness on the bondability of flip chip using an ultrasonic and to clarify interfacial structures between Au alloy bump and Al pad by ultrasonic bonding compared before to after thermal cycle test. Suitable Al thickness for the excellent initial Au/Al bonding without chip cracking are 0.8μm to 1.2μm. Chip cracks were occurred in thickness condition under 0.8μm because a thin Al layer could not reduce stress to a chip under an Al pad during ultrasonic bonding process. Intermetallic compounds between Au alloy bump and chip after reflows consisted of five Au-Al layers, and pure Al layer was remained. On the other hand, after temperature cycle test at 218/423K, intermetallic compounds between Au alloy bump and chip were changed into two kinds of Au-Al layers, so pure Al layer didn't existed. In addition, if thick intermetallic compound layers were existed around bonding region, bondability was easy to deteriorate by thermal stress due to a thermal cycle test, therefore open failure rate was rising when an Al pad thickness was 1.2μm.
Cross tension tests of resistance spot welded joints with varying nugget diameter were carried out by using 980MPa high strength steel sheet of 1.6mm thickness. In proportion as nugget diameter increase from 3√t to 5√t (t; thickness) cross tension strength (CTS) increased, while fracture morphology simultaneously transferred from interface fracture to full plug fracture. In case of interface fracture, circumferential crack initiation due to separation of corona bond arose at early stage of loading. The crack opening process without propagation was recognized until just before fracture and then the crack propagated to nugget immediately in brittle manner around CTS. In full plug fracture, main ductile crack initiation from notch-like part at the end of sheet separation occurred with sub crack initiated at early stage. The ductile crack propagated toward HAZ and base material to form full plug fracture. Mode I stress intensity factor was considered as a suitable fracture parameter for interface fracture because circumferential crack behaved pre-crack for brittle fracture in nugget region at final stage. Based on the FE analysis, mode I stress intensity factor was calculated 116MPa√m at CTS as fracture toughness for nugget. With respect to full plug fracture, ductile crack initiation behavior from notch-like part was expressed by concentration of equivalent plastic strain. On the assumption that ductile crack arose in critical value of equivalent plastic strain, the value was calculated 0.34 by FE analysis. Reasonable interpretation for interface fracture and full plug fracture in resistance spot welded joint was proposed due to first crack initiation by stress concentration, brittle fracture by using mode I stress intensity factor and ductile crack initiation by using equivalent plastic strain.
Improvement of the deformation capacity of the column-to-beam joint is an important theme for improving earthquake-resistant performance of building structures. One of the reasons decreasing the deformation capacity is the stress concentration against the beam flange by the scallop (access hole) existence. The non-scallop method is generally recommended to improve this problem, but it has large problem that is not able to apply to on-site joint process. The reinforce welding method around the scallop bottom has developed to be able to apply to on-site joint, and get performance more than the non-scallop method. Improving mechanism is combination with 1) decreasing the stress concentration, 2) increasing effective thickness, and 3) increasing total length of breaking line. The deformation capacity by reinforce welding method around the scallop bottom is maximum 3.2 times as for the conventional scallop method in the reverse repeating bend test using actual structure that beam flange has 19mm thickness and 490N/mm2 class steel. This improving effect is better than the non-scallop method.
This research describes a dissimilar metals joining of steel and aluminum (Al) alloy by means of zinc (Zn) insertion. The authors proposed a joining concept for achieving strong bonded joints between Zn coated steel and Al alloy. A eutectic reaction between Zn in the Zn coating and Al in Al alloy is used to remove the dense, strong oxide film on Al alloy surface at low temperature, thereby resulting in the formation of a thin, uniform Al-Fe intermetallic compound (IMC) layer at the joint interface, leading to a strong bonded joint. The ultimate aim of this research is to apply this joining concept in the resistance spot welding process for manufacturing vehicle bodies. This paper discusses the effectiveness of this joining concept by bonding galvanized (GI) steel sheet with Al alloy sheet, and galvannealed (GA) steel sheet with Al alloy sheet, by resistance spot welding. A precise observation of the combination of GI steel sheet and Al alloy sheet joint interface confirmed that a thin, uniform Al-Fe IMC layer can be formed with this process as a result of enveloping the oxide layer on the Al alloy surface in the eutectic melt and effectively evacuating it from around the periphery of the joint area. An excellent joint property was achieved by the realization of such a metallurgical bonding. As for the combination of GA steel sheet and Al alloy sheet, oxide film on Al alloy surface was removed by liquid phase formed by diffusion between Al and Fe-Zn alloyed coating layer; the formation of Al-Fe IMC layer was confirmed by observation of the joint interface. The Al-Fe IMC layer was thick and non-uniform, compared with GI steel and Al alloy. The difference is believed to be based on the difference in bonding process caused by different coating types. The region with Al-Fe IMC layer thickness of less than 2μm was defined as the effective bonded length. A clear correlation between the effective bonded length and the tensile strength was seen. An improvement of tensile strength was attempted by optimization of electrode shapes and welding conditions, considering differences in bonding processes of each metal combination, and a guideline for realizing high tensile strength was clarified. From above considerations, dissimilar metals joining between steel and Al alloy by the resistance spot welding was realized.
This research concerns a dissimilar metals joining of steel and aluminum (Al) alloys by means of zinc (Zn) insertion. The authors proposed a joining concept for achieving strong bonded joints between Zn coated steel and Al alloys. A eutectic reaction between Zn in the Zn coating and Al in Al alloy is used to remove the dense, strong oxide film on Al alloy surface at low temperature, thereby resulting in the formation of a thin, uniform Al-Fe intermetallic compound (IMC) layer at the joint interface, leading to a strong bonded joint. The ultimate aim of this research is to apply this joining concept in the resistance spot welding process for manufacturing vehicle bodies. As a practical issue characteristic to dissimilar metals joints, anticorrosion measures against electrochemical corrosion must be undertaken. If there is moisture near a dissimilar metals joint interface, electrochemical corrosion would progress. Therefore, a sealing function that could prevent moisture intrusion is required. By applying above mentioned welding process to a set of metals with thermosetting resin spread in between, we realized seal spot welding which would not only prevent moisture intrusion, but also retain high tensile strength. In this research, first, a cyclic corrosion test was performed on the seal spot welded joint of galvanized (GI) steel and Al alloy, and the anticorrosion measures were found to retain tensile strength and also secure sufficient corrosion resistance. Then galvannealed (GA) steel, a steel grade widely distributed in Japan, and Al alloy was bonded by seal spot welding, and following topics have been discussed. Complete removal of sealant from the joint interface is the key to realize high tensile strength joint, because remaining sealant would lead to reduction of tensile strength. Therefore, heat generation at the interface was monitored by measuring electrical current and potential difference between the two electrodes, and a precise temperature control was performed. Moreover, the bonding process was clarified by stepwise analysis of the joint interface using optical microscopy, and a guideline for producing strong joints was proposed. And finally, a TEM observation also confirmed that the interface structure of seal spot welded joint was the same as joints without the resin; a thin and uniform Al-Fe IMC layer was formed and a strong metallurgical bonding was achieved.
NASA is advancing the project of manned Mars exploration. In the future, Martian outposts and structures will be constructed. To realize this, welding technology is expected to be applied. The main atmospheric component of Mars is carbon dioxide, and the atmospheric pressure is approximately 700 Pa. In this study, welding experiments were carried out in a simulated Mars atmosphere of 99.5% carbon dioxide and a pressure of 700 Pa. Conventional Gas Tungsten Arc (GTA) welding and Gas Hollow Tungsten Arc (GHTA) welding, in which arc operating gas is allowed only to flow out from the electrode tip of a hollow tungsten electrode, were investigated. The arc discharge behavior and the melting characteristics in the simulated Mars atmosphere were studied. As a result, it was shown that GTA welding and GHTA welding might be applicable even in the Mars atmosphere.
Laser welding with oscillation laser beam enables control of the heat input distribution. In this study, we attempted to develop a narrow gap welding process with oscillation laser welding. This process is expected to prevent lack of fusion because the entire bottom of the groove can be melted by the oscillation laser. As the first step of the study, bead-on-plate welding experiments with an oscillation laser beam were performed to investigate the relationship between the welding conditions and welding results. The experiments revealed that the oscillation conditions strongly affect the welding penetration shape. It was clarified that the wire melting phenomena in oscillation laser welding differed from those of straight (non-oscillation) laser welding. Additionally, narrow gap laser welding experiments were performed to investigate the relationship between the oscillation conditions and gap width. The results confirmed the effectiveness of oscillation laser welding for narrow gap welding.