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The feasibility of welding a CuAlBe SMA by continuous drive friction welding was evaluated. The metallurgical state (annealed/quenched) before welding and frictional pressure (5 and 10 MPa) were varied and their effects on joint quality were analyzed. Static tensile tests, microhardness, thermal analysis by DSC, and optical microscopy were carried out to characterize the welded joint. The results indicated joints of excellent thermomechanical quality. The welding zones are well-defined, narrow, and have a very refined microstructure compared to the base metal. The phase transition temperatures along the welded assemblies were not changed when welding was performed on the quenched samples, except in the welding zone of the sample welded with 10 MPa. Maximum tensile strength was obtained by using maximum friction pressure during welding of the annealed alloy (quenching after welding). To fill the gap in bibliographical research in this field of study, this work innovatively presents the possibility of welding Cu-based SMAs by rotary friction, including the welding of quenched parts without the need for subsequent heat treatments and without compromising the shape memory effect.

This study was conducted to understand the relationship between various critical temperatures and the stability of the secondary phases inside the heat-affected-zone (HAZ) of welded Grade 91 (Gr.91) steel parts. Type IV cracking has been observed in the HAZ, and it is widely accepted that the stabilities of the secondary phases in Gr.91 steel are critical to the creep resistance, which is related to the crack failure of this steel. In this work, the stabilities of the secondary phases, including those of the M23C6, MX, and Z phases, were simulated by computational thermodynamics. Equilibrium cooling and Scheil simulations were carried out in order to understand the phase stability in welded Gr.91 steel. The effect of four critical temperatures—that is, Ac1 (the threshold temperature at which austenite begins to form), Ac3 (the threshold temperature at which ferrite is fully transformed into austenite), and the M23C6 and Z phase threshold temperatures—on the thickness of the HAZ and phase stability in the HAZ is discussed. Overall, the simulations presented in this paper explain the mechanisms that can affect the creep resistance of Gr.91 steel, and can offer a possible solution to the problem of how to increase creep resistance at elevated temperatures by optimizing the steel composition, welding, and heat treatment process parameters. The simulation results from this work provide guidance for future alloy development to improve creep resistance in order to prevent type IV cracking.

Inconel 718 alloy is widely used in applications that require advanced strength properties especially at high temperature conditions. Combust room walls, exhaust parts, jet tribune blades and gas tribune equipment are the most known using areas. This alloy can be welded with various fusion welding methods, but TIG (Tungsten Inert Gas) welding is preferred since, it provides simply application, mobility and low cost. This study was aimed to clarify that how adjusting the welding parameters and welding automatically can help to achieve promising mechanical properties before heat treatments. The welding experiments were conducted on three different welding current values and attention was paid to provide full penetration for each condition. The results showed that the highest welding current value which did not cause welding defects lead to decrease heat input due to the high transverse speed usage. Moreover, by automatically welding, the heat input was decreased to a minimum level that provided excellent tensile strength and elongation properties. Dendrites turned to cellular from colon. Hazardous zones, such as HAZ and PMZ, narrowed down. The Laves phase ratio and grain size also decreased. Microhardness results confirmed these microstructure observations. The crack observations after tensile tests showed that failures were near HAZ in high-heat input conditions. However, failures were observed in FZ for low-heat input conditions. Additionally, ductile fracture and fracture similar to cleavage mechanisms were observed together due to adjusting the parameters and automatization. [ABSTRACT FROM AUTHOR]

This study investigated the low-temperature fracture behavior of an 80-mm-thick low-carbon steel plate welded by submerged arc. The relationship between impact absorbed energy and ductility–brittle transition temperature (DBTT) based on the microstructures was evaluated through quantitative analysis on grain size and complex constituent phases using advanced EBSD technique. The microstructure formed differently depending on the heat affections, which determined fracture properties in a low-temperature environment. Among the various microstructures of the heat-affected zone (HAZ), acicular ferrite has the greatest resistance to low-temperature impact due to its fine interlocking formation and its high-angle grain boundaries.

Joining of thermoplastics with friction stir welding is a quite new subject, and there are not many studies on the subject in the literature. In this study, Polyethylene and Polypropylene plates 6 mm in thickness were successfully joined by using high-speed in the CNC vertical machining center. It was determined that the increase occurring in the tool translational speed increased the welding performance depending on the temperature in the weld zone. It was determined that the increase in the tool shoulder immersion depth was effective in the fibril lengths and temperature in the joining zone, the pressure arising decreased the mechanic features by affecting the microstructure. It was observed that the increase in tool rotational speed in the weld zone increased the crystallization rate, the increase in the immersion and waiting periods at the beginning of welding and the tool shoulder immersion depth decreased the crystallization rate. In the microstructure examinations performed with the scanning electron microscope, four different microstructures were found in the weld zone. These structures were classified as: 1-The area which is not affected by the heat, 2-Joining interface, 3-Stirring zone affected thermomechanically, and 4- The zone remaining under the unjoined welding tool stirring tip part. [ABSTRACT FROM AUTHOR]

Based on the continuous extrusion machine LLJ350, experiment and Deform numerical simulation were conducted to analyze the metal flow and welding process during the continuous extrusion of AA6063 aluminium alloy with double billets. The microstructure and mechanical properties of extrusion welds were investigated through optical microscopy, scanning electron microscopy, and tensile tests. The results reveal that the oxides on the billet surface participate in the metal flow and affect the microstructure and mechanical properties of the extrusion welds. The extrusion weld exhibits bud morphological characteristics on the cross-section of the extrudate, and the welding quality of the bottom portion is superior to that of the upper portion. The welding lines are mixed with fine grains of several micrometers, and the surrounding area contains grains with a size of several hundred micrometers. When the specimens fracture at the weld, the macrofracture forms with a striped surface; by contrast, the microfracture displays a streaky structure, which includes striped protrusions and small dimples of several micron diameters. And it is also found that the extrusion welds slightly affect tensile strength, but markedly influence extrudate elongation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The concept of "solidification process percentage" is proposed. • The relationship between the welding experiment and simulation is established. • The G/R threshold of welding morphology evolution for AZ31 Mg alloy is obtained. • The G × R threshold of welding grains size evolution for AZ31 Mg alloy is obtained. The relationship between the evolution of microstructure morphology (planar, cellular, columnar and equiaxed) and grain size (2.5 μm, 5.0 μm, 7.5 μm and 10.0 μm) of a specified metal and the calculated solidification parameter (G/R , G × R) of temperature gradient (G) and solidification rate (R) is calculated by comparing the "solidification process percentage" of the welding experiment and simulation. Taking pulsed laser single spot welding as the object, the varying solidification parameters and corresponding microstructure of liquid–solid interface are obtained by adjusting the pulsed closing shapes. The results show that the calculating method of the solidification parameter threshold of the welding microstructure evolution by using the solidification process percentage is reliable and the evolution threshold of microstructure morphology and the grain size of AZ31 magnesium alloy are obtained. The research lays a theoretical and practical foundation for the establishment of the solidification parameter threshold system of the welding microstructure evolution. [ABSTRACT FROM AUTHOR]

This paper investigates the stress corrosion cracking (SCC) behavior of welded API X70 pipeline steel in simulated underground water using the slow strain rate test, fractographic characterization by scanning electron microscopy, and potentiodynamic polarization techniques. SCC susceptibility of the heat-affected zone (HAZ) is demonstrated to be dependent on two factors: the effect of the microstructure in the HAZ on electrochemical reactions and the effect of the mechanical property on SCC occurrence. Electrochemical experiments indicate that the microstructures in the HAZ, especially the softened microstructure, can significantly facilitate the processes of hydrogen evolution when cathodic potential is positive to −1050 mV. However, when the cathodic potential is below −1050 mV, the cathode current densities of different microstructures are close to one another and greatly increase because of the decrease of the applied potentials. The SCC behavior is consistent with the electrochemical results. Under −650 and −850 mV, SCC is most likely to occur in the softened region, and under −1200 mV, SCC occurs in both the softened and hardened regions. [ABSTRACT FROM AUTHOR]

In the present paper, the results are reported of an investigation dealing with the inclusions, microstructure and mechanical properties of self-shielded flux cored welds with different aluminium contents. Results show that the total number and number density of inclusions in the low aluminium weld are higher than those of the high aluminium weld. However, the average size and the contamination rate of inclusions in the low aluminium weld are 0·77016 μm and 0·022%, which are lower than those of the high aluminium weld. The weld with a low aluminium content contains finer inclusions and the weld with a high aluminium content contains mainly coarser inclusions. There are remarkable differences in microstructure between the welds with different aluminium contents. The reheated zones in the weld made using flux no. 1 are larger than those in the weld made using flux no. 2, which are occupied by skeletal δ ferrite columnar crystals. As a result, a drastic reduction in impact toughness is observed in the high aluminium weld. Fracture examination shows that the low aluminium fracture surface consists mainly of small ductile dimples and a quasi-cleavage fracture area. The fracture surface of the high aluminium weld comprises mainly larger dimples and a cleavage fracture area. Inclusions in the low aluminium weld are mainly small Al2O3–MgO spinel with an approximate round shape, and some AlN inclusions. In the case of the high aluminium weld, inclusions are almost all large AlN. Finally, the results of thermodynamic analysis agree with the trends observed in the experimental data. [ABSTRACT FROM AUTHOR]

This study investigated the low-temperature fracture behavior of an 80-mm-thick low-carbon steel plate welded by submerged arc. The relationship between impact absorbed energy and ductility–brittle transition temperature (DBTT) based on the microstructures was evaluated through quantitative analysis on grain size and complex constituent phases using advanced EBSD technique. The microstructure formed differently depending on the heat affections, which determined fracture properties in a low-temperature environment. Among the various microstructures of the heat-affected zone (HAZ), acicular ferrite has the greatest resistance to low-temperature impact due to its fine interlocking formation and its high-angle grain boundaries. [ABSTRACT FROM AUTHOR]