Rate of absorption of CO2 laser beam energy during bead-on-plate welding of SM400 mild steel plate was measured. A 10 kW industrial CO2 laser welding equipment was used in this study.
In the first part of the experiments, bead-on-plate welding was made on a water-cooled steel plate placed in a welding jig made of acrylic plastics. The surface of the steel plate was machine-finished. The laser beam energy absorbed into the steel plate was calculated from the measurements of the inlet and the outlet water temperatures, the water flow rate and the beam-on time. Rate of absorption was calculated as the ratio of the absorbed beam energy to the total beam power.
In the second part, bead-on-plate welding was carried out on either a machine-finished, a paint-coated on machine-finished or a ground-finished steel plate. Absorption was also evaluated.
In the third part, heat conduction loss to the acrylic welding jig was evaluated and found to be approximately 5%. The results of measurements and calculation were reported and discussed.
It was estimated in this study that absorption of CO₂ laser beam energy during bead-on-plate welding of a mild steel plate at a laser power of 10 kW was in the range from 30 to 50%.

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The travelling phenomena of the rotational plane arise in friction welding of different diameter materials and dissimilar materials, and friction surfacing is carried out by the phenomena. It has been revealed that in friction surfacing the real rotational contact plane exists at the central part of the rotational plane, the surfaced metal apparently transferrs from a filler rod to a plate through the real rotational contact plane owing to the travelling phenomena of the rotational plane, the area of this plane decreases with increasing rotational speeds and friction pressures, and the diameter of this plane {dc=2*√W/(πρa)} is calculated by a mass the surfaced metal (W) and a friction upset distance (a).
This study also revealed that the friction welding of different diameter materials and dissimilar materials had the same phenomena of friction surfacing concerning the real rotational contact plane and a consideration for the decreasing mechanism of this real plane was described.

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Emission spectra in KrF excimer laser induced plasma were measured with time resolution of the order of tens ns in laser materials processing of iron target; excitation temperature of the laser-induced plasma was determined by a Boltzmann plot of Fe (I), and electron density was determined from an intensity ratio of Fe(I) and Fe(II) lines. At a power density of 8×10² W/m², the temperature and electron density were approximately 17000-18000 K and 5×10²⁶ m^-3 at the end of laser pulse of 30 ns, respectively. The absorption of KrF excimer laser was also measured in the laser induced plasma by using the probe laser beam travelling parallel to the target surface, which is split from the main KrF excimer laser. The absorption coefficient in the plasma thus obtained reached as high as approximetely 4×10³ m^-1 at the end of laser pulse duration. This value agreed well with the value calculated from the inverse-Bremsstrahlung theory when the excitation temperature and electron density obtained by the spectral method are used. This indicates that considerable amount of laser energy can be absorbed in the laser induced plasma without reaching the target via the absorption in the plasma at the later part of the laser pulse.

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In order to improve the friction weldability of tungsten to copper, a commercially pure tungsten was friction-welded to an oxygen free copper with the aid of intermediate layers of various metals. Intermediate layers employed were foils of Ti, Al, Nb, Ni, Fe and Ag of thickness 20-30μm. Burn-off rates during friction welding with intermediate layers except Ag were greater than that observed without an intermediate layer. Especially, intermediate layers of Ti, Nb and Fe increased the burn-off rate remarkably. Intermediate layers except Ag became finer or thiner particles during friction process and was mixed with Cu forming stratified microstructures. When intermediate layers of Ti and Al were applied, intermetallic compounds of Ti-Cu and Al-Cu systems were formed in the mixed layer. As the friction time was increased, the tensile strength of joints was increased, and reached almost saturated values depending on the intermediate layers. The tensile strength of joints with intermediate layers of Ti, Nb and Fe was increased rapidly than that of the direct welding without an intermediate layer, and reached higher levels. Especially, joints with the intermediate layer of Nb were fractured in the HAZ of copper at friction times of 4 s or more, while joints with the other intermediate layers were fractured at weld similarly to the case of the direct welding. Friction torque and heat input during welding with the intermediate layers of Ti, Nb and Fe were much greater than those of friction welding without an intermediate layer, suggesting that the increases in friction torque and heat input accelerated the burn-off and the rise in tensile strength of joints.

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The effects of surface treatment of skin steel sheets on resistance spot weldability were examined about electro-conductive vibration damping steel sheets (VDSS) which contained metal particles in resin layer. Zn-Fe coating was applied as a surface treatment. Though electric resistance between the skin sheets decreased, pin-hole became easy to be formdd due to the existence of the coated layer. And, that was promoted by increase in coating thickness. The pin-hall had a shape of the hollow which spread parallel to the sheet surface. This was very different from a globular type of pin-hall which was seen in VDSS made of bare skin sheets. When the pin-hall occurred a ralatively long period of high voltage (about 20 V) was observed on voltage wave form. Those results suggested that the pin-hole was generated by arc electric discharge, however that of VDSS made of bare skin sheets was generated by joule heating. Arc discharge was occurred by opening an electric circuit between metal particle and skin sheet due to a evaporation of coated layer.
On the other hand, it is well known that electrode face is deformed by a number of spot welds on coated steel sheets. Using such deformed electrodes, another type of defect that was local fusing of skin sheet adjacent to electrode was observed. This phenomenon was caused by delay of exclusion of resin.
From above test results, it was clear that the coated steel sheet used as the skin sheets was promoting weld defects. However, good weldability of VDSS made of coated skin sheets was achieved by optimizing adding condition of metal particles.

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Bonding strength of coating to substrate in low pressure plasma spraying was investigated and the effect of reverse transferred arc treating before spraying was studied. The results are summarized as follows,
(1) For the bonding strength test in low pressure plasma spraying, instead of the conventional adhesive, vacuum brazing process using Ag-Cu-In-Ti active filler metal at 1023 K was proposed and the propriety has been confirmed.
(2) By the above test method, it was proved that the bonding strength of low pressure plasma sprayed coating is over 100 MPa. However, the bonding strength of coating pretreated by blasting before spraying fell down and fluctuated when the average roughness, Ra of the substrate surface was less 2μm.
(3) Reverse transferred arc treating after blasting has enhanced the bonding strength of low pressure plasma sprayed coating, especially when the roughness, Ra of substrate before spraying is less than 2 μm. It is considered that the projections formed on the substrate surface by reverse transferred arc treating were buried into coating and performed the pile effect.

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We have demonstrated that the application of ultrasonic vibration changes the tensile strength of austenitic stainless steel joints brazed with Ag-based filler metal. In this paper, we employed six kinds of filler metals which were prepared in a laboratory and studied the relation between the tensile strength of the joints and the microstructure of the brazed layer in order to obtain more understanding in terms of the factors and mechanisms governing the increase in the tensile strength of the joints.
It seems that the factors which increase the tensile strength of the brazed joints with applying ultrasonic vibration are : 1. Achievement of grain refinement in brazed layer ; 2. Acceleration of the dissolution of base metal into filler metal followed by solid-solution hardening of brazed layer through the dissolved elements ; 3. Tensile strength increase due to the shift of the brazed layer composition to eutectic one at which eutectic alloys show the highest tensile strength ; 4. Solid-solution strength-ening of brazed layer resulting from the increase in crystallization of solid solution composed of main elements in filler metal.

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A measurement system was developed to measure adhesion forces between solids. Adhesion forces were measured in an ultra high vacuum (UHV) chamber of an Auger electron spectroscopy (AES). Contacts were made between a silicon wafer and a gold sphere with a radius of about 200μ m. The specimens were sputtered by argon ion before the contacts. No adsobates were observed in Auger spectra obtained from the sputtered surfaces, although the ion sputtering could induce some damages on their surface.
In the present study, we discuss the influence of the ion sputtering on the adhesion forces. The adhesion forces were measured after the ion sputtering as a function of the applied load from 0 to 1000μN. The adhesion forces obtained after the 3 kV-3.6 ks sputtering were larger than measured after the 1 kV-3.6 ks sputtering. The adhesion forces measured after the 1 kV-10.8 ks sputtering were larger than measured after the 1 kV-3.6 ks sputtering. Assuming the elastic theory, it can be intepreted that the surface energy of materials changes under conditions of the ion sputtering.

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In a high-current density spot welding, the large electromagnetic force yields between electrodes. This electromagnetic force bring about the fluctuation of the loading force, and then, it has some adverse effect on weldability. The fluctuation of the loading force is changed by stiffness, friction, or response of a loading system. In this report, we designed a loading system which is able to control the movement of an electrode, and clarified the dynamic property in turning on electricity. The loading force is affected by the electromagnetic force and the thermal expansion. The electromagnetic force increases proportionally to the square of the maximum current in the reverse direction of loading, and as a consequence, it reduce the actual loading force to the specimens. The electrode movement is controlled by a stopper and a spring assembled into a loading system. In a rigid loading system with large spring constant, the electrode movement by the electromagnetic force is restrained, and so the loading force is increased by the thermal expansion. The other hands, in a loading system with small spring constant, the loading force is decreased, because the electrode movement caused by the electromagnetic force is larger than the thermal expansion.

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A loading force is very significant factor for the resistance spot welding. In a high-current density spot welding, the electromagnetic force increases proportionally to the square of muximum current in the reverse direction of loading, and as a consequence, it reduce the loading force. The fluctuation of the loading force in welding has direct effects upon the weldability. In this report, we investigate the influence of loading property on weldability and exibit the optimum laoding system in a high-current density spot welding. In a loading system with small spring constant, a nugget forms at the condition of the low current but the defect forms easaily at the interface, because an electrode moves in response to the electromagnetic force and the loading force is decreased in welding. In a loading system with large spring constant, it is difficalt to form the welded joint, because, the movement of an electrode is restrained and the loading force is increased by the thermal expansion. This trend is exposed remarkably for the material with a high thermal conductivity such as Al alloy. In a high-current density spot welding, it is very important to design the loading system under consideration of the electrode displacement by the electromagnetic force and thermal expansion.

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This report deals with a detection and estimation of change in the characteristics of molten metal such as heat transfer and damped oscillation during an arc welding with a pulsed current for monitoring the bead formation of the back side of a thin plate.
An idea of the detecting method had been proposed in 1974 (Japanese Patent No.876269, U.S. Patent No.3988567, British Patent No.1493524) and to apply the idea to a new welding system to be developing, reasonableness and effectiveness of the method are reconsidered and made clear.
It is possible that the depth in a partially penetrating weld is roughly estimated from detecting the waveform and the phase difference of change in the heat rediation on the back side due to the difference of heat transfer in welding a plate.
In addition, it is possible that the stability in the back side bead formation as well as the back bead size in fully penetrating weld are estimated from detecting the waveform of change in the heat radiation due to the damped oscillation of the molten metal in the back side.

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To complete all position fully automated GTA welding, wire height location control is necessary. Wire height is affected by weld pool movement according to welding position change, melting spray transfer with gravity, curling during uncoiling and disturbance of wire melting condition from heating arc. To solve these problem we checked the voltage change between wire and base metal from the melting phenomena of wire. We developed the control technique to keep the wire height always suitable by measuring the short-circuiting counts (N) and short-circuiting percentage of time (At) from wire melting phenomena.
At the same time to prevent bad effect to the electrode accompanied by wire height irregularity we developed the electrode abnormality judgement software.

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The effects of the Mg content and bonding temperature on the morphology and crystalline structure of interfacial oxides in the diffusion-bonded joint have been investigated mainly by TEM observations for Al-Mg binary alloys with Mg contents from 0.06 to 2.0at%. For all the alloys employed, the oxide at the joint interface altered gradually from amorphous films to crystalline particles 10-100 nm in size, as the bonding temperature was increased, and the amorphous oxide film was annihilated at lower bonding temperatures, as the Mg content was increased. The crystalline oxide particles at the joint interface were identified as A₁₂MgO₄, at Mg contents from 0.06 to 0.6at% and as MgO at Mg contents from 1.3 to 2.0 at%, independently of the bonding, temperature. At Mg contents from 0.9 to 1.1at%, the crystalline oxide particles changed from MgO to Al₂, MgO₄, passing through a range where MgO and Al₂MgO₄, coexisted, as the bonding temperature was increased. The ranges of Mg contents and bonding temperatures where the crystalline oxides of Al₂MgO₄, and MgO formed can be roughly explained thermodynamically by assuming that these crystalline oxides were formed through reductive reactions of the superficial oxide film of aluminum by Mg. It was suggested that the slight difference between the thermodynamically calculated ranges and the experimental could be attributed to the contribution of the interfacial energies between the crystalline oxides and the Al matrix. Auger electron spectroscopic analyses of a fractured surface of a joint bonded at a low bonding temperature revealed that Mg atoms highly concentrated in the amorphous oxide film prior to the formation of the crystalline oxide particles, suggesting that the concentration of Mg caused a driving force for the formation of the crystalline oxide particle from the amorphous fiilm.

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Synthetic ruby has been brazed to molybdenum rod using Ag-Cu eutectic filler including active metal of 1-8 mass%Ti, in order to investigate on the relation between the brazing condition and the bonding strength.
The strength of the joint was evaluated by tensile test and the brazing interface was examined by SEM and EPMA.
According to the tensile test, bonding strength of the joint brazed with 1 mass%Ti-Ag.Cu was less than 20 MPa independent on bonding temperature. Anotherside, bonding strength of the joint brazed at 1123 K-1173 K using 2-8 mass% Ti-Ag.Cu, was more than 100 MPa, and above 1223 K, it was reducing with raising of brazing temperature. Especialy the bonding strength of joint brazed at 1223 K using 8 mass%Ti-Ag.Cu showed remarkable reduction.
The examination of brazing interface by SEM and EPMA showed that ruby was corroded by brazing filler and reaction layer composed by Ti, Cu, Al and 0 was formed at bonding interface. According to the corrosion test, raising the brazing temperature and increasing the Ti content in the brazing filler hasten the corrosion of ruby.
Wiht advancing of ruby corrosin, Al and O made from corroded ruby diffused into the reaction layer and the content of these elements increased in this area. These experimental results showed that bonding strength of joint was reducing with advancing of ruby corrosion at brazing interface.
This suggests that advancing of ruby corrosion at bonding interface brings the brittleness of reaction layer and the bonding strength is reducing.
Anotherside, the preferential movement of Ti to bonding interface was hasten with advancing of ruby corrosion and it was assumed that the movement of Ti to bonding interface was concern to ruby corrosion.

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Both side heating method which is proposed by authors in previous report is the effective stress control method for pipe butt weld joint. Non-dimensional parameters that control the effect of this method, and conditions which should be satisfied to get sufficient effect in actual application are clarified in this paper. Followings are the rusults which are made clear in this paper.
(1) The parameters which control effect of both side heating are βl, βW and K (=σ/EαT). Where β, l and W are size parameter (β⁴=3(1-υ²)/r²t²), distance from weld center line and width of heating region, and r, t, σ, E, υ, a and T are radius of pipe, thickness, stress at joint region, Young's modulus, Poisson ratio, thermal expansion coefficient, and temperature difference. The relation between parameters βl, βW and non-dimensional stress K are figured out, and this relation shows the combination of parameter range which control the residual stress at weld inside to compression state. These parameters and the combination of their ranges are verified by FEM analysis.
(2) The locations of temperature measurement and the conditions of temperature at each location which should be satisfied to get sufficient effect in actual application are proposed. These conditions for actual application are verified through experiment of both side heating on two size of stainless steel pipe weld joints based on the proposed condition.

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The conventional manual enclosed arc welding process, which has been. employed as a field welding process for rails, has shortcomings that the liquation cracks are likely to occur at the boundaries of coarsened austenite grains in the heat-affected zone.
This paper describes the susceptibility of HAZ liquation cracks for rails and the causes of crack incidence. Experiments have been done to define the critical carbon content of weld metal and critical welding condition necessary for avoiding the cracks by employing some electrodes with various carbon content. And also, in order to discuss the crack susceptibility and the crack causes of rail steels comparing to those of general structural steels, the synthetic test has been done to simulate the HAZ liquation cracks.
The main experimental results are as follows :
(1) The crack incidence increases with decreasing weld metal carbon content when the difference in the carbon content between the weld metal and rail steel is 0.3% or more.The cracks are eliminated when the former difference is less than 0.2%.
(2) The cracking tendency increases with increasing electrode diameter and weld current or weld heat input.
(3) The liquation crack susceptibility of rail steel is nearly equal to that of plain carbon steel, for which the crack dose not become a subject of discussion in actual welded joint.
(4) The main cause of HAZ liquation crack for rail enclosed-arc welding is the considerable difference of liquidous & solidous temperature depended on the difference of carbon content between the weld metal and base metal.

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Laser welding has the advantage of high welding speed and provides low heat distortion. Thus, laser welding is very attractive process for joining thin steel sheets. In this study, static and fatigue strength of laser welded lap joints were investigated.
Tensile strength of the lap joints was determined by the weaker one between the strength of base metal and that of weld metal. The strength of the base metal was estimated with the tensile strength and thickness, and the strength of the weld metal was estimated with the hardness and width of the weld metal. Thus, the calculated strength coincided with the experimental strength of the joint with different tensile strength and thickness of the base metal.
Fatigue crack initiated at the edge of weld metal, and propagated along the fusion line to the free surface. We employed fracture mechanics to evaluate the fatigue strength of the lap joint with different thickness. Stress intensity factor of the lap joint was calculated with the analysis of J. Chang and R. Muki.
We employed criterion of Erdogan and Sih to evaluate the fatigue strength. By this criterion, the fatigue strength was well characterized.
As a result, this approach, which was originally developed to evaluate fatigue strength of spot welded lap joints, was also effective for fatigue strength of laser welded lap joints.

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The previous reports have clarified that the quality of gas pressure welds is influenced by local area expansion factor (α) and weld temperature (T) ; hot shearing method helps evaluate the quality of welds ; and that a line flaw, if bonding work is poor, is caused by tensile stress which occurs at shearing edge.
In this paper, a study about the influence of bulge removal on weld's strength, and the reliability of quality estimation by hot shearing method of steel bar gas pressure welds is reported. The conclusions are as follows :
(1) The quality of gas pressure welds scarcely declines by hot shearing.
(2) Whether hot shearing is applied or not, the influence of various factors, such as welding process, surface condition, and gap between surfaces, on weld's strength is constant.
(3) In bending test, the acceptable rate of welds submitted to hot shearing is lower than that of welds without hot shearing.
(4) The fatigue strength of welds is scarcely influenced by hot shearing.
(5) The reliability of hot shearing method is higher than that of penetrant method or ultrasonic method.

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The purpose of the present investigation is to improve the fatigue strength of a non-load-carrying cruciform fillet welded joint by applying abrasive water jet kinetic energy to the weld toe region. FEM analysis, measurements of residual stress and hardness at toe region and 0-tension fatigue test of the fillet welded joint were performed for analyzing the improvement of fatigue strength. Fatigue failures invariably occurred at toe region. Main results obtained are summarized as follows:
(1) Fatigue limit of a water jet treated joint could be improved to about 1.6-2.0 times (180-224 MPa) that of a joint as-welded by suitable water jet treatment (LP-pass number: W07538, W05010, W10038-3, W07538-3, W10038).
(2) The reasons for such an improvement are considered to lie in tensile residual stress being decreased ; hardness increased ; and stress concentration decreased at toe region, depending upon the condition of water jet treatment.

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Experimental conditions for the fabrication of intermetallic compound coatings by DC plasma spraying of Ni/Al mechanically alloyed powders have been investigated.
The results obtained are summarized as follows ;
(1) In atmospheric plasma spraying, APS, the obtained coating was composed of two or more phases : Ni-rich phase, and Alrich phase. Ni/Al MA powder seemed to be subjected to phase separation during plasma spraying. On the other hand, homogeneous intermetallic coatings were obtained by low pressure plasma spraying, LPPS, due to the diffusion of two element in the sprayed powders.
(2) The dominating factor for phase separation for MA powders during plasma spraying seemed to be the heat flow from surrounding plasma ; the contributions of other factors, such as, mixing of the powder, composition of working gas, oxidation of the powder and acceleration force in plasma flame, were negligible.
(3) By low pressure plasma spraying or HVOF spraying of MA powder, the intermetallic coating can be fabricated easily. Even in the APS process, intermetallic coating can be obtained by the spraying of sizeable MA powder.

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