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•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.
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.
In order to avoid softening and improve the mechanical properties of the aluminum alloy welded joints,the butt test of 5A06 aluminum alloy was carried out with FSW,and the welded joints were ...processed into metallographic samples and tensile samples of a certain size under the conditions of a rotating speed of 1 200 r/min and a welding speed of 150 mm/min,the effect of deep cryogenic treatment (DCT) time on microstructure and mechanical properties of friction-stir-welded joints of 5A06 aluminum alloy was investigated.The experiments were carried out by microstructure observation test,micro-hardness test and tensile test to characterize and analyze the joint organization and mechanical properties.The experiment results show that DCT can refine the grain and promote the precipitation of the second phase,thus the mechanical properties of the joints are improved.The tensile strength and elongation of the joints can reach 385.3 MPa and 17.2% respectively,which are increased by 7.4% and 23.7%,respectively after 12 h
•Welding of a Cu-based shape memory alloy by continuous drive rotary friction.•Welded joints with high efficiency and no change in the functional properties.•The metallurgical state and the friction ...pressure determine the welding time.
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.
The effect of microstructural changes in 304 austenitic stainless steel induced by the processes of gas tungsten arc welding (GTAW) and laser-beam welding (LBW) on the pitting and stress corrosion ...cracking (SCC) behaviors was investigated. According to the in situ observations with scanning reference electrode technique (SRET) and the breakdown potentials of the test material with various microstructures, the GTAW process made the weld metal (WM) and heat-affected zone (HAZ) more sensitive to pitting corrosion than base metal (BM), but the LBW process improved the pitting resistance of the WM. In the initiation stage of SCC, the cracks in the BM and HAZ propagated in a transgranular mode. Then, the crack growth mechanism changed gradually into a mixed transgranular
+
intergranular mode. The cracks in the WM were likely to propagate along the dendritic boundaries. The crack initiation rate, crack initiation lifetime and crack propagation rate indicated that the high-to-low order of SCC resistance is almost the same as that for pitting resistance. High heat-input (and low cooling rate) was likely to induce the segregation of alloying elements and formation of Cr-depleted zones, resulting in the degradation in the corrosion resistance.
The laser braze-welding technique was aimed to join a low alloyed zinc coated steel used in automotive industry, with a deformable, aging hardenable aluminum alloy from the 6xxx series using as ...filler material a AlSi12 wire. The heterogeneous joint was obtained by welding of aluminum alloy with the filler wire and by brazing of molten aluminum alloy together with the filler wire on the surface of a zinc coated steel which remained in solid state. The results showed that by using a proper heat input, the zinc coated steel was brazed without a melting process by the aluminum alloy which was in liquid state. On the interface between the zinc coated steel and the welded seam, a thin layer (the thickness was 6 to 8
m) formed consisting of star (Al-Fe-Si) or needle shape (Mg-Al-Fe-Mn) intermetallic phases.
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.
Termoplastiklerin sürtünme karıştırma kaynak tekniği (SKK) ile birleştirilmesi oldukça yenidir ve konu hakkında
literatürde çok fazla çalışma yer almamaktadır. Bu çalışmada, 6 mm kalınlığındaki ...Polietilen (PE) ve Polipropilen
(PP) levhalar CNC dik işleme merkezinde yüksek devirler kullanılarak başarılı bir şekilde birleştirilmiştir. PE
levhaların birleştirilmesinde kaynak takım devir hızı ve kaynak başlangıcında dalma ve bekleme süreleri
değiştirilmiş, PP levhaların birleştirilmesinde ise takım omzu dalma derinliği değiştirilerek kaynak performansı
üzerindeki etkileri incelenmiştir. Takım devir hızında meydana gelen artışın, kaynak bölgesinde oluşan sıcaklığa
bağlı olarak kaynak performansını arttırdığı, kaynak başlangıcında dalma ve bekleme süresinin kaynak için gerekli
olan ısının elde edilmesinde ve bu ısının kaynak hattı boyunca taşınması üzerinde etkili olduğu tespit edilmiştir.
Takım omzu dalma derinliğindeki artışın birleşme bölgesindeki fibril boyları ve sıcaklık üzerinde etkili olduğu,
oluşan basıncın mikroyapıyı etkileyerek mekanik özellikleri düşürdüğü belirlenmiştir. Kaynak bölgesinde takım
dönme devrindeki artışın kristallenme oranını arttırdığı, kaynak başlangıcında dalma ve bekleme süresi ile takım
omzu dalma derinliğindeki artışın ise kristallenme oranını azalttığı gözlemlenmiştir. Taramalı Elektron
Mikroskobu (TEM) ile yapılan mikroyapı incelemelerinde kaynaklı bölgede dört farklı mikroyapı bulunmuştur.
Bu yapılar; 1- Isıdan etkilenmeyen bölge, 2-Birleşme ara yüzeyi, 3- Termomekanik olarak etkilenen karışım bölgesi
ve 4- Birleştirilmeyen kaynak takımı karıştırıcı uç kısmı altında kalan bölge, şeklinde sınıflandırılmıştır.
This study was performed to investigate microstructure of dissimilar friction stir welds manufactured with AA6061-T6 and AZ31 alloy sheets. Dissimilar butt joints were fabricated under the ‘off-set’ ...condition that tool plunge position shifted toward AZ31 from the interface between AA6061-T6 and AZ31. Optimized tool rotating speed and its traveling speed were selected through a lot of preliminary experiments. Electron back-scatter diffraction (EBSD) technique was applied to measure texture in the stir zone (SZ). Grain size distribution and misorientation angle distribution were also obtained. A remarkably fine-grained microstructure was observed in the SZ. Randomized or weaker plane orientations were formed in the SZ of AA6061-T6, while rotated basal plane orientations were concentrated in the SZ of AZ31. Average size of recrystallized grains was measured as just 2.5–4.5 μm. The fraction of high-angle boundary in the SZ of AA6061-T6 increased and that of low-angle boundary in the SZ of AZ31 decreased compared with the base metals.
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.
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