Undercut and humping bead are the common defects that limit the maximum welding speed of tandem pulsed GMA welding. In order to raise the maximum welding speed, effects of the angle and distance between leading wire and trailing wire on the bead formation of high speed welding are investigated. The undercut and humping bead is attributed to the irregular flow of molten metal towards the rear part of the weld pool. This irregular flow can be prevented by the trailing wire with a push angle from 5 to 13 degrees that provides a proper component of arc force towards the welding direction. Moreover, the irregular flow is also related to the distance between leading wire and trailing wire and the flow becomes regular when the distance is in the range from 9 to 12mm. As a result, the maximum speed of tandem pulsed GMA welding is improved markedly.
In tandem pulsed GMA welding the stabilization of accumulated molten metal between the leading arc and the trailing arc, the presence of enough molten metal below the trailing arc, and the reduced velocity of molten metal flow towards the rear part of the weld pool are essential to improve the maximum welding speed. These conditions can be attained by adjusting the ratio of the leading arc current to the trailing arc current. A maximum welding speed as high as 4 to 4.5 m/min is achieved by setting the current ratio to a value ranging from 0.31 to 0.5, which corresponds to an reduction in average velocity of molten metal flow at locations 4 to 7 mm behind the trailing arc.
In order to clarify the physical relation among a tungsten electrode, an arc, a heat transfer to anode and a penetration of a base material in TIG welding process, the electron temperatures of the arc plasma, the distributions of current density and heat intensity on the anode surface, and the cross-sectional areas of the weld penetration of a stainless steel are respectively measured at a 100 A in argon TIG arcs with different conditions of arc lengths and conical tip angles of tungsten electrode. The temperature measurements of electron in the arc plasma by using a laser scattering method show the same temperature close to the tungsten electrode independently of the arc length. But, the electron temperature close to the anode decreases with increase of the arc length. The maximum values of current density and heat intensity on the anode surface also decrease with increase of the arc length. These experimental results are discussed with relation to the cross-sectional areas of the weld penetration. As a result, it is concluded that the electron temperature close to the anode and current density on the anode surface decide the heat intensity distribution on the anode surface and then the heat intensity remarkably dominates the size of the weld penetration in TIG welding process. Furthermore, different conical tip angle of tungsten electrode affects the electron temperature and also the cross-sectional areas of the weld penetration.
In order to clarify the interfacial reactivity between A6061 and pre-coated metals in surface-activated pre-coating technique, the bond interface of diffusion-bonded joints of A6061 to Ag, Cu or Ni was analyzed. Diffusion bonding of A6061/Ag, Cu or Ni was carried out at 660-723K for 0-3.6ks applying 9.8MPa in vacuum. Eutectic temperature of A6061-Ag, Cu or Ni alloy was measured preliminarily by DTA technique. The lowest eutectic temperatures of A6061-Ag, A6061-Cu and A6061-Ni systems were 680±10K, 700±10K and 720±10K, respectively. SEM observation revealed that the reaction layer was formed at the bond interface. The Ag-Al, Cu-Al and Ni-Al intermetallic compounds were identified in the reaction layer. It was elucidated that the reaction layer growth could be expressed by parabolic growth law, and that the incubation time for reaction layer formation was increased in the order of Ag
The SUS316L stainless steel is widely used as the machinery parts for chemical plant and power plant. In order to improve the wear- and corrosion-resistance quality of parts, usually, the plasma process has been adopted to clad Co-based and Ni-based alloys powder on parts surface of SUS316L stainless steel. In the present work, the CO2 laser (2.4kW-CW) cladding of low residual stress and small distortion, and plasma cladding were investigated to deposit WELPC-6 Nickel alloy powder on the cylindrical prod for power plant. The smooth clad bead was obtained by CO2 laser cladding. The phases of clad layer were investigated by an optical microscope, scanning electron microscopy (SEM), X-ray diffractometer (XRD), electron probe microanalysis (EPMA), and energy-dispersion-spectrometer (EDS). The microstructures of clad layers belong to a hypereutectic structure. Primary phases consist of Cr7C3 and CrB. The eutectic structure consists of γ-(Ni, Fe)+Cr23C6 or γ-(Ni, Fe)+Cr2B. Comparing with the plasma process, the fine microstructures, low dilutions, and high Vickers hardness were obtained by CO2 laser cladding.
According to the specification for Highway Bridges, the minimum weld size is determined so that the leg length, S, satisfies the condition of S>=√2t, where t is the thickness of a plate. However, when the thickness exceeds 40mm this standard requires the S value larger than the maximum of one pass welding, which could lead to the decrease of the welding execution efficiency. Why this standard regulates the weld size is to avoid cold cracking by escaping the rapid cooling. But escaping the rapid cooling is not the only method to avoid cold cracking. In this study, we examine the cold cracking susceptibility and the HAZ hardness distributions of the fillet welds using 50mm thick plates whose PCM ranges from 0.21% to 0.27%. We also carry out the heat conduction analysis to evaluate the effect of the test piece size. Using the present results, we discuss the validity of the today's standard of the √2t regulation.
In order to predict the distortion generated by welding with high accuracy, distortion with fillet welding was measured by three-dimensional photographic measurement. Then, the experiment was simulated by three-dimensional thermal elastic-plastic analysis by FEM. The important matters that should be noted on predicting the distortion with high accuracy were shown by comparing with the results of the experiment and those of the analysis. The results of measuring temperature could be accurately simulated by non-steady state thermal conduction analysis based on FEM. In carrying out the elastic-plastic analysis, four conditions (equilibrium equation, constitutive equation, condition of compatibility and yield condition) should be satisfied. In welding, the temperature largely changed from a melting temperature to a room temperature. So, yield stress of materials largely changed, too. In particular, yield stress becomes about zero above 700°C. The analysis should be carried out under the yield condition that equivalent stress generated in temperature increment ΔT did not exceed yield stress of materials at high temperature above 700°C. It should be sufficiently recognized that the obtained results were not reliable if the yield condition was not satisfied. Angular distortion generated in fillet welding could be accurately predicted by regarding the weld metal as a deposited metal not assuming that a deposited metal zone was a simple triangle. Specifying an influence factor on longitudinal bending distortion was difficult because the absolute value was small. However, it was indicated that the reasonable result could be obtained by regarding the weld metal as a deposited metal because the absolute value of longitudinal bending distortion at pass (2) (the second pass) of which restraint was severer became smaller than that at pass (1) (the first pass).
The low cycle fatigue (LCF) behavior of as-cast Sn-0.7mass%Cu lead-free solder and compared with those of conventional Sn-37mass%Pb solder were investigated at strain rate 0.1%/s under various temperatures, R.T. (room temperature), 80°C, 120°C. In addition, the relationship between the surface feature in the LCF test and the fatigue life of these solders at R.T. were investigated. The fatigue life of Sn-0.7Cu decreased with increasing temperature. And the fatigue life of Sn-0.7mass%Cu was better than that of the Sn-37mass%Pb solder at R.T. and 80°C. The surface deformation as fine meshes during the LCF test of Sn-0.7mass%Cu did not appear until 10% of fatigue life. Although over 10% of fatigue life, surface deformation that was caused by micro cracks and these link up occurred with increasing number of cycles.
Authors report experimental results on mechanical properties including weldability of rolled H section steels. The investigation is performed on arc- electric furnace steels and those of blast furnaces. The experiment was divided into the base-metal examination and the weld examination, and was carried out. The examination carried out chemical analysis, a tensile test, a hardness test, a Charpy impact test, nonmetallic inclusion examination, etc. And the reappearance thermal cycling test which feeds back the thermal hysteresis of actual welding was also carried out.
This study deals with nondestructive evaluation of the solder ball joints in BGA package. In order to establish the fast, two-dimensional, non-contact and non-destructive method for the evaluation of solder joints, a new technique based on the infrared thermograph was developed, in which the surface temperature of solder ball joints was measured in the thermal cycle with abrupt cooling after heating. Two parameters were used to evaluate the bonding state of the solder ball joints. One parameter is the temperature change of solder ball in the thermal cycle with the thermal shock due to abrupt cooling, which shows large decrease in poor bonding and slight decrease in good bonding. Another one is the temperature ratio between the solder ball and surrounding molded area, or dimensionless temperature. This value decreases with applying the thermal shock to poor bonding joints, while good solder ball joints keeps constant values regardless of thermal shock. These differences in two parameters are caused from the different thermal conductivity at the bonding interface of solder ball, which were confirmed by the FEM analyses of solder ball joints. It was also confirmed that the second parameter was a preferable parameter for the evaluation of solder ball joints, since the initial heating temperature as well as cooling time did not influence it.
The present paper describes the seizure phenomena at welded interface during steel pipe friction welding. The relationship between friction speed and initial torque was clarified, and the relationship between relative speed and seizure temperature at the welded interface was estimated from the experimental results. The seizure phenomenon of the base metal was clarified by a constant temperature friction test in which the friction surfaces were rubbed together at various temperatures and loaded pressures in an electric furnace. Then, the seizure temperature at the friction surface was obtained by constant temperature friction tests. The experiments produced the following summarized results. (1) The friction torque curve had wear and seizure stages until the initial torque when pipes were welded at low friction speed. The wear stage time decreased with increasing friction speed. The initial torque decreased with increasing friction speed when pipes were welded at the same friction pressure, and increased with increasing friction pressure. (2) The seizure temperature at the welded interface was calculated by using the relationship between the torsional shear strength of the base metal at its seizure temperature and the measured initial torque. The seizure temperature for a low relative speed at the welded interface was lower than that for a high relative speed. (3) The maximum friction torque increased with increasing friction temperature at the same loaded pressure, and they increased with increasing loaded pressure at the same friction surface temperature by constant temperature friction tests. (4) The friction surface of the base metal began to seize when loaded pressure and friction surface temperature reached or exceeded 30MPa at 423K, and 90MPa at 323K, respectively.
Friction stir welding (FSW) has become an important joining process of aluminum alloys in various industries. Conventional FSW process, however, is difficult to apply to the welding in dissimilar metals. In our series of research, the welding between aluminum alloy and steel has achieved by means of friction stirring. This is a promising way to realize a high performance joint in dissimilar metals. In the present study, the weldability between 6063 and S45C by means of friction stirring was investigated. By optimizing the welding conditions, such as a tool configuration and a rotating speed, higher welding speed more than 1000 mm/min was achieved. The mechanical properties of the weld joints fabricated were evaluated with the normal tensile test and hardness test. The specimens were fractured in the portion of the lowest hardness area in aluminum alloy. In the microstructure observation with SEM, thick intermetallic compound layer on the interface region was not detected.
It is examined whether an extrapolation method can presume temperature in faying surface of high density polyethylene round bar because this material is very small heat conductivity and low melting point. As a result of this examination, it is possible that this method is used for measurement of temperature. Therefore, this study have used this method, and the effect of friction welding condition on temperature distribution in faying surface of polyethylene is investigated with a brake type friction welding machine which was built as a trial for polyethylene. The experimental results are as follows; 1) When installation location of thermocouple was below 0.5mm interval, the extrapolation method can presume temperature distribution in faying surface. 2) When friction pressure was P1=0.10MPa, the temperature distribution in faying surface was almost the same (about 452–497K). 3) When friction pressure was P1=0.25MPa, the temperature of middle (about 639K) and outside part (about 646K) was very high in spite of one of center part (about 387K) was low and not melted. Therefore, this temperature distribution was not uniformity. 4) The error of installation location of 0.1mm of thermocouple has occurred to measured error of about 5% because axial temperature gradient was steep. Therefore, this material was required sufficient care, when temperature in faying surface was measured by this method.
Diffusion bonding of SUJ2 and Ti-6Al-4V has been carried out in the bonding temperature range from 1173 to 1273K for 3.6 ks at the bonding pressure of 1.96MPa. The effects of the reaction phases formed at the bonding interface on the bonding strength were analysed. Main results obtained were as follows: (1) With increasing bonding temperature, the species of the main reaction phases at the bonding interface change from FeTi2 to Fe2Ti via FeTi
by the diffusion of iron atoms of the SUJ2 into the Ti-6Al-4V phase.
(2) With increasing the bonding temperature, tensile strength and elongation of the joints first increased and then decreased, whereas the
maximum Vickers hardness of the reaction phase first decreased and then increased. Therefore the changes in the strength properties
were well correlated with the change of the maximum Vickers hardness of the reaction layer.
(3) On the other hand, diffusion of Ti, Al and V atoms of the Ti-6Al-4V into the SUJ2 phase was comparatively small. It can be explained
by the formation of a TiC phase at the bonding interface of the SUJ2 side which protects the diffusion of these atoms. In spite of its high
Vickers hardness, fracture did not occur at the TiC phase because of its small width under 3μm.
(4) Fractured parts of the tensile tests of joints were the reaction phase part mainly composed of the above mentioned Fe-Ti intermetallic
compound. Therefore, tensile strength and elongation of the joints were found to be influenced mainly by the species of intermetallic
We tried to join steel to Al-Mg alloy using a resistance spot welding method. The effect of Mg in Al-Mg alloy on the strength and the interfacial microstructure of the joint was investigated. Additionally, the effect of an insert metal of commercially pure aluminum, which was put into the bonding interface, on the joint strength was investigated. The following results were obtained. The cross tensile strength of a joint between SS400 steel and commercially pure aluminum (SS400/Al) was high and fracture occurred in the aluminum base metal. However, the strength of a joint between SS400 and Al-Mg aluminum alloy was remarkably low and less than 30% of that of the SS400/Al joint. An intermetallic compound layer developed so thickly at the bonded interface of the SS400/Al-Mg alloy joint that the joint strength decreased. The intermetallic compound layer developed more thickly as Mg content in the Al-Mg alloy increased. Using an insert metal of commercially pure aluminum containing little Mg successfully improved the strength of the SS400/Al-Mg alloy joint and the strength was equivalent to that of the base metal.
The metallographic factor controlling the strength of friction-welded interface of mild steel to Al-Mg alloy A5083 has been investigated by TEM observations. The bond strength, estimated from the tensile strength of a specimen with a circumferential notch at the interface, rose rapidly with an increase in friction time, and then reduced. A maximum strength of 311 MPa was obtained at a friction time t1 of 2 s (rotation speed = 20 s-1, friction pressure = 40 MPa, and forge pressure = 230 MPa). At a friction time of 1 s, an interfacial layer about 100 nm wide that consisted of (Fe,Mn)Al6 and Mg2Si was formed at the interface, and an Al oxide layer of width less than 10 nm was observed between the (Fe,Mn)Al6 layer and mild steel substrate. The joint bonded at t1=1 s was fractured mainly along the Al oxide layer. In a joint showing the highest bond strength (t1 = 2 s), no Al oxide layer could be detected between the mild steel substrate and interfacial layer, which consisted of (Fe,Mn)Al6, Fe4Al13, Fe2Al5, and Mg2Si. The width of the interfacial layer was increased to about 300 nm at t1=2 s. The fracture occurred along the IMC layer of (Fe,Mn)Al6, Fe4Al13 and Fe2Al5. At t1 of 4 s, a layer of MgAl2O4 about 100 nm in width was observed in addition to the intermetallic compounds observed at t1= 2-3 s. The crack on the tensile test was propagated mainly along the MgAl2O4 layer. Thus the controlling phase of the bond strength was altered from the Al oxide film, intermetallic compound layer, and MgAl2O4 layer, depending on friction time. The formation mechanisms of the observed interfacial phases are discussed from a metallographic point of view.