Friction Stir Spot Welding (FSSW) has been practically used to the construction of aluminum car-body in the automotive application. In this study, the weld strength and factors governing the weld strength in friction stir spot welded aluminum alloy 6061-T6 was examined. The weld strength increased with the process time during FSSW up to 3 s, beyond which it decreased. The fracture path changed from the lapped interface into the shoulder edge as the process time increased, and the maximum strength was obtained at the process time when the transition of the fracture path occurred. The cross-sectional microstructure depended on the threads on the probe surface, i.e. the elliptical zone was formed in the stir zone by the threads, but effect of the thread on the weld strength was hardly found. The present study suggests that the weld strength was strongly related with size of the well-consolidated region which was larger than the elliptical zone observed in the vicinity of the exit hole.
In order to produce a high strength brazed joint of A5056 aluminum alloy containing magnesium of about 5 mass %, the authors applied the flux-free brazing method with the aid of ultrasonic vibration to the aluminum alloy by selecting pure Ag foil as brazing filler metal and examined the effect of brazing conditions on the joint properties. The main results obtained in this study are as follows. At the brazing temperature of 570°C just above the eutectic point of Al-Ag binary system, applying of ultrasonic vibration for 4.0s provided the brazed joint with the maximum tensile strength and the strength decreased with the applying time. When the brazing temperature was varied from 550°C to 580°C and the applying time of ultrasonic vibration was kept constant at 4.0s, the joint brazed at 560°C attained the maximum tensile strength and fractured in the base metal. It was found that using a pure Ag foil as brazing filler metal successfully brazed A5056 aluminum alloy and the joint strength was equivalent to that of the base metal. Fracture of the joint was prone to occur along (Al3Mg2+Al-solid solution) phase with high hardness formed at the grain boundary of the base metal. The amount of the hard (Al3Mg2+Al-solid solution) phase increased with the ultrasonic applying time and the brazing temperature. It seemed that the increase of the hard (Al3Mg2+Al-solid solution) phase mainly caused the brazed joint strength to decrease.
The joinability of unalloyed titanium and the bond strength of similar-titanium welded joints by ultrasonic welding were investigated. It turned out that sound welded joints of similar-titanium were obtained by using the jig for fixing both base metals. In the case of non-fixing and fixing the lower base metal, sound welded joints weren't usually obtained due to the slip between the two base metals. Producing welded joints having sufficient bond strength required a certain threshold value of the ultrasonic energy. When the ultrasonic welding was carried out under the condition where the ultrasonic energy was higher than a threshold value (approximately 2000 W•s), the welded joints were fractured within the titanium base metal but not at the interface. The values of the bond strength were associated with the fixing method and the surface roughness of the base metals. The bond interface was joined metallurgically for the most part, although some small voids were observed on the bond interface by SEM and EPMA observation.
This paper deals with the creep strain generated during PWHT by both experimental data of inherent strain and numerical results of that. The experiment of inherent strain was done by using Cr-Mo steel and SHT490 steel. The initial yielding stress and 0.2% proof stress were measured at high temperature. The main conclusions obtained were as the following: (1) the creep strain of PWHT is generated during the heating process. (2) the creep strain of PWHT is estimated by the strain hardening. (3) the creep strains of Cr-Mo steel and SHT590 steel can be estimated by the equation with the stress index and the strain index being not depend on the kind of steel, but only one creep constant changing by the kind of steel.
To make progress of laser-arc hybrid welding, especially which is applied to thick steel plate, it is essential to get remarkable synergic effect of deep penetration. It is suggested that the effective process is combined hollow cathode TIG with high beam quality laser. Penetration of hollow TIG/YAG hybrid welding was investigated by numerical analysis. A keyhole surface model taken account of laser beam parameter product (BPP) was developed. The calculated keyhole surface profiles of coaxial hybrid welding are wider and deeper than that of YAG laser alone. As a result, 1-pass butt welding of 20mm thickness steel plate was achieved in condition of BPP=0.9mm · mrad at laser power 1.8kW. To confirm numerical results, coaxial hybrid welding tests with hollow cathode TIG was conducted. The welding penetration was about 2 times as deep as YAG laser alone. It was found that coaxial hybrid welding of hollow TIG/YAG had large synergic effect.
A friction stir welding process, in which a rotating tool without a probe was employed, was applied to a lap joint of aluminum plate. The thickness of aluminum plates were 0.5 mm. The new tool shapes were developed. The tops of the tool were dome shapes. In this process, the rotating tool was plunged into the aluminum plate. The tool rotating axis is vertical to the specimen surface, and then moved to the welding direction at a speed of 20 mm/s. Tool rotation speed was 18,000 rpm. At tool plunge depths of 0.1 mm or over, it was possible to weld the two plates. At tool plunge depth of 0.1 mm, its joint was fractured at weld interface. At tool plunge depth of 0.2 mm or over, the joints were fractured at the stir zone of upper plate or the heat affected zone of lower plate. Based on the observation of the hardness profiles and the thickness change of weld area, controlling factors of the joint strength were discussed.
Adhesion between a semi-infinite elastic body and a rigid surface with a sinusoidal roughness is solved. The solution is exactly same as that of K. L. Johnson (Int. J. Solids Structures, v.32, p.423 (1995)), although the different method is used for the derivation. Based on the solution, possibility of reversible joining process is considered. Conditions for the complete contact and the partial contact are clearly expressed as the function of the surface roughness, the elastic constant, the work of adhesion, and external pressure. The adhesion stress is expressed as the function of the other parameters. It is suggested that an infinite stress is required to separate the complete contact. The reversible joint is possible if it is designed under the partial contact condition. A critical area contact parameter is found, less than which the reversible joint should be designed.