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    Effect of powder-pack aluminizing on microstructure and oxidation resistance of wire arc additively manufactured stainless steels
    (Elsevier Science Sa, 2023) Gurol, Ugur; Altinay, Yasemin; Gunen, Ali; Bolukbasi, Omer Saltuk; Kocak, Mustafa; Cam, Gurel
    This study investigated the effect of powder-pack aluminizing treatment on the high-temperature oxidation of ER307 stainless steel components fabricated by wire arc additive manufacturing (WAAM) during isothermal oxidation at 1000 degrees C for 5 h, 25 h, and 50 h. Scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD), X-Ray fluorescence (XRF), nanoindentation testing, and oxidation testing were used to characterize the aluminized and non-aluminized samples produced by WAAM. The results showed that the powder-pack aluminizing increased the surface nano-hardness up to 13.95 GPa and the modulus of elasticity up to 159 GPa, as well as improving the microstructure of WAAM ER307 stainless steel. Indeed, aluminide coatings remained stable up to temperatures exceeding 1000 degrees C, and the growth of hematite, the main oxide phase, was inhibited by a preferential alumina growth (Al2O3), resulting in an improvement in oxidation resistance in the range of 46-70 %. In addition, owing to the advantages of low-temperature aluminizing, the microstructure, mechanical properties, and oxidation resistance of these alloys have been improved without causing sigma phase formations, which constitute a significant problem in high-temperature heat treatment of stainless steels.
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    Effects of Initial Temper Condition and Postweld Heat Treatment on the Properties of Dissimilar Friction-Stir-Welded Joints between AA7075 and AA6061 Aluminum Alloys
    (Springer, 2014) Ipekoglu, Guven; Cam, Gurel
    In this study, dissimilar AA7075-O/6061-O and AA7075-T6/6061-T6 butt joints were produced by friction stir welding (FSW), and postweld heat treatment (PWHT) was applied to the joints obtained. The effects of initial temper condition and PWHT on the microstructure and mechanical properties of the dissimilar joints were thus investigated. It was demonstrated that sound dissimilar joints can be produced for both temper conditions. A hardness increase in the joint area (i.e., strength overmatching) was obtained in the joints produced in the O-temper condition, whereas a hardness loss was observed in the joint area of the joints obtained in the T6 temper condition. It was also well demonstrated that PWHT could be used in order to improve the joint properties for both O and T6 joints provided that the joint is defect-free prior to subsequent heat treatment.
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    Effects of temper condition and post weld heat treatment on the microstructure and mechanical properties of friction stir butt-welded AA7075 Al alloy plates
    (Springer London Ltd, 2014) Ipekoglu, Guven; Erim, Secil; Cam, Gurel
    In this study, AA7075-O and AA7075-T6 Al alloy plates were friction stir butt welded using two sets of weld parameters in order to investigate the effects of temper condition prior to joining and post weld heat treatment on microstructure and mechanical properties of the joints. Another goal of the work is to determine the possibility of restoring the loss of strength in the joint area experienced in welding of this alloy in the age-hardened condition by subsequent heat treatment. The study revealed that the friction stir welding resulted in a strength undermatching when the alloy joined in T6 condition while a significant strength overmatching was obtained in the joints produced in O temper condition. The post weld heat treatment led to a significant recovery in the strength of the joints produced in T6 condition, thus a significant increase in the joint performance. On the other hand, it led to a decrease in the joint performance value of the joints produced in O temper condition although the strength was increased. Furthermore, the post weld heat treatment resulted in abnormal grain growth in the joint area the degree of which depends on weld parameters used and the prior temper condition.
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    Investigation into mechanical properties of high strength steel plates welded with low temperature transformation (LTT) electrodes
    (Inderscience Enterprises Ltd, 2012) Ozdemir, Okan; Cam, Gurel; Cimenoglu, Huseyin; Kocak, Mustafa
    Controlling the amount of distortion and tensile residual stresses plays an important role during welding of high strength steels. The amount of distortion and residual stresses in high strength steel welds may be reduced and compressive residual stresses can be induced by lowering the transformation temperature with the use of low-transformation-temperature (LTT) welding electrodes. In this study, high strength Domex 500 plates (500 mm x 300 mm x 7 mm) were welded with conventional high strength electrodes and LTT filler electrodes with a diameter of 2.5 mm. The objective of the study is to compare the mechanical and microstructural properties of high strength steel joints (i.e., Domex 500) produced using both conventional electrodes and newly-developed prototype LTT electrodes.
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    Investigation into the Influence of Post-Weld Heat Treatment on the Friction Stir Welded AA6061 Al-Alloy Plates with Different Temper Conditions
    (Springer, 2014) Ipekoglu, Guven; Erim, Secil; Cam, Gurel
    In this study, the effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of friction stir butt-joined AA6061 Al-alloy plates both in O and T6-temper conditions was investigated by detailed microstructural investigations and micro-hardness measurements, in combination with transverse tensile testing. It was determined that the PWHT might result in abnormal grain growth (AGG) in the weld zone particularly in the joints produced in O-temper condition depending on the weld parameters used during friction stir welding. The PWHT generally led to an improvement in the mechanical properties even if AGG took place. Thus, the post-weld heat-treated joints exhibited mechanical properties much higher than those of respective as-welded plates and comparable to those of the respective base plates. (C) The Minerals, Metals & Materials Society and ASM International 2013
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    INVESTIGATION OF THE EFFECT OF TEMPER CONDITION ON THE FRICTION-STIR WELDABILITY OF AA7075 Al-ALLOY PLATES
    (Inst Za Kovinske Materiale I In Tehnologie, 2012) Ipekoglu, Guven; Kiral, Binnur Goren; Erim, Secil; Cam, Gurel
    Al-alloys are widely used in the transportation industries due to their low density and excellent formability properties. These alloys, which are problematic in fusion-welding processes, can be successfully joined by friction-stir welding. Particularly high-strength AA7075 alloy is considered to be non-weldable by fusion welding. Friction-stir welding, being a solid-state joining technique, can also be successfully used in joining other difficult-to-weld alloys. In this study, 3.17-mm-thick, AA7075 Al-alloy plates both in the O- and T6-temper conditions were joined by friction-stir welding using four different weld parameters. Microstructural and mechanical characterizations of the joints produced were obtained with detailed optical microscopy investigations, extensive hardness measurements and tensile tests. The effect of temper condition on the joint performance was determined in addition to the effect of the weld parameters on the joint quality.
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    Recent Developments in Friction Stir Welding of Al-alloys
    (Springer, 2014) Cam, Gurel; Mistikoglu, Selcuk
    The diversity and never-ending desire for a better life standard result in a continuous development of the existing manufacturing technologies. In line with these developments in the existing production technologies the demand for more complex products increases, which also stimulates new approaches in production routes of such products, e.g., novel welding procedures. For instance, the friction stir welding (FSW) technology, developed for joining difficult-to-weld Al-alloys, has been implemented by industry in manufacturing of several products. There are also numerous attempts to apply this method to other materials beyond Al-alloys. However, the process has not yet been implemented by industry for joining these materials with the exception of some limited applications. The microstructures and mechanical properties of friction stir welded Al-alloys existing in the open literature will be discussed in detail in this review. The correlations between weld parameters used during FSW and the microstructures evolved in the weld region and thus mechanical properties of the joints produced will be highlighted. However, the modeling studies, material flow, texture formation and developments in tool design are out of the scope of this work as well as the other variants of this technology, such as friction stir spot welding (FSSW).