Journal of Advanced Joining Processes最新文献

In this study, submerged friction stir welding (SFSW) was performed to weld 6 mm thick AZ31B Mg alloy plates, aiming to explore the impact of rotation speed on microstructure and tensile behavior. The water medium was used to submerge the samples. The SFSW was conducted at three different speeds (815, 960, and 1200 rpm), to assess the impact of rotation speed on SFSWed joint performance. As the rotation speed increased from 815 to 960 rpm, tensile strength increased plateauing over a range of the rotation speed. However, a significant drop in tensile strength occurred at 1200 rpm due to the formation of void defects. The SZ exhibits a size and width increment in the lower part with increasing rotation speed. The hardness of the stir zone (SZ) gradually rose with increasing rotation speed from 815 to 960 rpm. Fracture locations were observed in the thermal-mechanically affected zone (TMAZ) adjacent to the SZ at a rotation speed of 815 rpm, and in the heat-affected zone (HAZ) adjacent to the TMAZ at a rotation speed of 960 rpm. The joint welded at 1200 rpm fractured within the SZ. This study offers valuable insights into the welding and joining field, particularly regarding their mechanical characteristics.

Automatic welding equipment has replaced human welders in the nuclear industry for safety issues and uniform and high welding quality. However, automatic welding equipment cannot predict porosity defects. So, the weldment must be inspected by non-destructive testing. This inspection was a costly and time-consuming process, and it applies to each weldment even if it welded same material. To improve the welding efficiency, a weld porosity detection system of the same weld material with different material thicknesses was needed. This paper proposed a machine-learned porosity detection system for 3.0 mm plates with welding arc sound data from the pulsed gas tungsten arc welding (P-GTAW) process of 1.6 mm plates. Ensemble-Empirical Mode Decomposition (EEMD) was used to divide the arc sound signal according to the pulse period of P-GTAW. Fast Fourier transform (FFT) was used to convert the arc sound into frequencies for features extraction according to porosity. The validity of these weld frequency features was confirmed through k-fold cross-validation across various machine learning techniques, with evaluation of F-1 scores against experimental weld sounds.

Shaft-shaped parts work normally in wear-resistant conditions. Over time, the shaft might experience wear and fail to maintain the required size, affecting its workability and efficacy. This study examines the hardfacing layer quality of a restored steel shaft obtained through resistance welding. The researchers of this study designed nine welding conditions according to Taguchi's experimental matrix and applied each to experimentally weld steel shaft samples. A recovery welding machine system, which includes a resistance seam welding machine combined with a designed fixture, was used to weld the samples. The experimental results revealed that the welding layers’ surface is flat and has no surface defects. Meanwhile, the hardfacing layer and the retorted shaft surface have good cohesion, as observed through macrostructure photography. The hardness and wear resistance of the hardfacing layer were relatively high and closely resembled those of a new high-frequency quenched steel shaft. The influence level and the relationship of the welding parameters on hardness and wear resistance were also considered in this study. In addition, this study proposes the appropriate welding conditions for obtaining the highest hardness and the smallest worn metal weight. The findings presented in this study offer valuable insights for mechanical manufacturers engaged in the reconditioning process of shafts, aiding in time and cost savings.

There are still some technical issues involved in laser welding of aluminum alloys, such as porosity, cracking, deformation, and so forth. In this study, AA6061-T6 sheets of 2.54 mm in thickness were welded by a disk laser in the bead-on-plate with two different welding parameter sets. Full penetration depths were achieved with decent surface appearances for both cases. The digital image correlation method was successfully applied in experiments to identify material model parameters of tensile welded specimens from various weldment regions. The identified parameters were utilized to numerically simulate the uniaxial tensile tests of laser-welded specimens. The effect of welded joint geometry on global tensile responses was investigated in experimentally-guided finite element modeling. With the help of X-ray computed microtomography, internal defects of the welded bead were detected and used as an input variable in the simulations. Strain development was observed through experimental and numerical data. The results showed that axial deformation was initiated at the top surface of welded metals. The considerable axial deformation occurred at the bottom surface (weld root) of the welded joint just before failure. The numerical results indicated that the geometry of welded joints greatly affected tensile responses. The results also concluded that the diameter of a single void significantly influenced tensile responses compared to its distributed location and the total volume of multiple voids with smaller sizes. Compared between the two sets of welding parameter sets used in this study, the welded joints of this particular AA6061-T6 material with the first parameter set of 2.40 kW laser power and 1.27 m/min traveling speed employed could give better tensile properties and be verified by both experimental and numerical results.

During the layer-by-layer build-up in the Direct Energy Deposition (DED) - Arc additive manufacturing (AM) process, the distance between the contact tube and the workpiece, effectively the welded layer, changes. Since the weld paths are predefined by the path planning software, a constant Contact Tube to Workpiece Distance (CTWD) and weld bead height is assumed. However, even small changes in geometry, such as crossovers of weld paths, result in higher weld beads than assumed. Similarly, an incorrectly assumed bead height as input to the path planning will result in a change in the CTWD. The sum of the deviations of the real weld geometries from the assumed ones in the path planning can greatly influence the CTWD. This implies that the dimensional accuracy may be significantly compromised. This research presents an approach for a general indirect measurement method using the welding current to obtain the CTWD during the actual welding process. A real-time process control method is implemented and validated using the mechanically controlled short arc and the pulsed arc process. Varying process parameters are used to validate the general applicability for a specific material. For the mechanically controlled short arc process, the model underestimates the measured CTWD by a mean error of 3.4 mm. The pulse process is overestimated by a mean error of 2.2 mm. The standard deviation for the pulse process with 1.3 mm is slightly smaller than for the short arc process with 1.7 mm.

Semitubular self-piercing riveting is an important and well-established mechanical joining process. A new approach, which involves the use of high strain hardening rivet materials, has the potential advantage of increasing resource efficiency in rivet production by eliminating the normally necessary post-treatment of the rivets by means of heat treatment and coating. However, as the high strain hardening of the rivet materials leads to extraordinarily high tool loads during rivet forming, process fluctuations can be particularly critical. For example, fluctuations in the dimensions of the semi-finished products used can influence the forming process itself, but also the quality of the formed rivets, which in turn can affect the subsequent joining process and the joint formation. An increased reject rate or premature tool failure caused by this is detrimental to the resource efficiency of the entire process chain. Therefore, a fundamental knowledge of the cross-process chain cause-and-effect relationships in conjunction with fluctuating billet dimensions is needed and is acquired within this research work. The investigations show that the forming and the joining process as well as the manufactured components themselves are influenced by the billet dimensions. The forming forces and tool stresses rise with increasing billet volume. Tool failure due to excessive or uneven stress can be the result. As the billet volume increases, the head diameter and the head thickness of the rivets increase. Consequently, the joining process and the joint are also indirectly influenced by the billet volume. With increasing volume, the joining force rises and, due to the increase in the head diameter, so does the joint strength. Knowledge of the detailed relationships is therefore highly relevant for the successful use of high strain hardening rivet materials.

Tensile residual stress (TRS) is a well-known factor that deteriorate the integrity of welded joints. Fatigue failure is accelerated by the existence of TRS introduced during the welding process. There have been efforts in the last two decades to develop filler alloys that can reduce TRS by introducing compressive residual stress (CRS) to oppose the TRS in high strength steel welded joints. These works are based on the theory of austenite (γ) to martensite (α’) transformation and the filler is often called a low transformation-temperature (LTT) alloy. Many studies have reported that the fatigue strength (FS) of weld joint made with LTT alloy is many times better than that of the conventional fillers. It is reported to be particularly useful in the repair of high strength steel structures. However, studies on the fatigue crack growth (FCG) behaviour of these LTT alloys is scarce. In this work, we developed Fe-CrNiMo based LTT weld metal composition, assessed its FCG behaviour and compared the results with that of a conventional welding wire (ER70S-6). It is found that ER70S-6 weld metal obtained under relatively fast cooling is extremely tough, but the associated heat affected zone (HAZ) has poor resistance to FCG which obscured the benefit of the tough weld metal. High heat input or condition that results to slow cooling of the ER70S-6 weldment deteriorates its resistance to FCG. Unfortunately, despite its low martensite start temperature of 231±7 and the anticipated beneficial effect of induced CRS, the LTT alloy studied had the lowest FCG resistance. The LTT alloy appears to have an intrinsic microstructural feature or a ‘fault line’ that reduced its resistance to FCG. While the LTT alloy weld metal has poor resistance to FCG, the associated HAZ resisted FCG more than the HAZ associated with ER70S-6 weld metal. It is observed that aligning the ER70S-6 weld metal perpendicular to the crack front produced the highest resistance to fatigue crack initiation and propagation. In the case of ER70S-6, it is believed that the weld metal induced a CRS at the notch tip which resulted to the high fatigue resistance. In the case of the LTT alloy, perpendicular alignment of the weld metal produced slight improvement.

This work investigates the fatigue crack growth behavior of adhesive joints under pure modes I and II within epoxy matrix composites reinforced with unidirectional carbon fibers. Experimental tests are made using Double Cantilever Beam (DCB) and End-Notched Flexure (ENF) setups for modes I and II respectively, considering exposure periods of one week and twelve weeks in a salt spray chamber. Control specimens are also studied for comparison.

Static tests were conducted to securely establish the levels of Energy Release Rate (ERR) that were subsequently used to obtain the fatigue initiation curves (G-N) and fatigue crack growth curves (G-da/dN). A probabilistic model based on a Weibull distribution is applied to analyze fatigue initiation data.

The fatigue limit in mode I, for all aging periods, is around 25 % of the static strength, while in mode II, it is around 20 %. These results are very close at all aging levels (0, 1, and 12 weeks). From this, it is inferred that aging in a saline environment of the studied joints does not have a significant impact on the fatigue limit.

In the crack growth zone, for mode I, the velocity is higher in the specimens aged in both periods than in the unaged specimens. The same cannot be said for mode II, where a clear trend cannot be appreciated.

Friction-stir (FS) welding was used for the first time to successfully join Mg–Zn–Y–Al–La alloy extrusions containing the long-period stacking ordered (LPSO) phase. Plastic flow produced fine α-Mg grains of sizes 2.0–2.5 μm with random orientation in the stir zone (SZ) and stir-affected zone (SAZ), as well as fine fragmentation of the LPSO phase. No strong (10$\overline{1}$0) textures were observed in the SZ and the SAZ of the FS-welded Mg–Zn–Y–Al–La alloys. The tensile deformation behavior and texture evolution were evaluated via mechanical testing using digital image correlation and electron backscatter diffraction measurements. The FS-welded Mg–Zn–Y–Al–La alloy exhibited a tensile yield strength of 248 MPa, a joint efficiency of 1.12, and sufficient ductility owing to texture weakening caused by rare-earth texture formation, which suppressed geometric softening. However, no damage was observed at the incompatible boundary between the SZ and SAZ, which is typically a fracture point. The FS-welded Mg–Zn–Y–Al–La alloy fractured in the heat-affected zone on the advancing side, where the temperature was higher than on the retreating side, owing to recrystallization promotion.

This paper is the first to report successful application of self-pierce riveting (SPR) in thin-walled high pressure die cast (HPDC) aluminium for use in automotive applications. HPDC fabricated AA356x coupons were joined to conventional rolled RC5754 material. A set of industry-relevant joint stacks were created. Priority stacks included cast material as the upper layer. More challenging joints were also fabricated with cast material as the lower layer. Automotive industry key performance indicators were used to assess joint integrity. The key results and recommendations were:

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  HPDC aluminium was revealed to be able to be joined to rolled aluminium according to vehicle manufacturer automotive standards.

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  Process boundaries were established for satisfactory SPR joints across a range of material thicknesses and stack types.

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  SPR joint solutions were proven in the most challenging stacks with cast material as a bottom layer.

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  Greater variability in the joint key performance indicators was observed in stacks where the cast alloy is the top layer.

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  Microstructural analysis of both AA356x and RC5754 revealed differences in grain structure and hardness and it is proposed that this accounts for the increased variability.

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  Strength testing of lap shear joints demonstrated the mechanical effectiveness of an SPR joint including cast material. Under normal vehicle operating conditions, the performance of joints including cast material was equivalent to that of rolled material only joints. Following yielding, joints including cast material suffered a more brittle failure mode leading to differences in performance under crash scenarios.