Electric arc spray coating (EASC) is a method used to protect aluminum materials from corrosion, but there is no optimization in the literature using Al99.99 coating wire for EN AW 7020 alloy. The presented study aims to optimize the EASC process parameters (voltage, amperage, spray distance, and number of passes) for EN AW 7020-T6 aluminum samples. The experimental design of selected factors was made with Taguchi L 9 (3 4 ) orthogonal array and the aftermath of optimum values for coating were obtained with the TOPSIS multicriteria decision-making method. Output parameters respectively; pull-off strengths of coating were determined in compliance with the ASTM D4541 standard, the coating thicknesses were measured with a 3D profilometer, and the porosity values for cross-section were analyzed by optical microscope according to ASTM E2109 standard. After determining the optimum parameters, the substrates were coated and the crystallographic analysis of the coated samples was performed by XRD technique and electrochemical corrosion potential values were determined by galvanostat/potentiostat device in 3.5% NaCl solution. In exfoliation corrosion (EXCO) tests performed according to ASTM G34-1 standard, EXCO damage was detected on the surfaces of uncoated samples and graded as EA. In the EXCO tests with coated samples, no corrosion damages were observed on the coatings and they were rated with an N grade. The Al99.99 coating significantly improved the EXCO resistance of EN AW 7020-T6, reducing the corrosion rate by almost 100%. EXCO tests with uncoated and coated samples proved that the Al99.99 coating acts as a barrier to protect the substrate. Optimized Al99.99 coating offers a promising solution to improve the corrosion resistance of EN AW 7020-T6 aluminum alloys and extend their service life in harsh environments.

In this study the effect of T6 heat treatment, two-step aging treatment and ultrasonic impact peening on the exfoliation corrosion behavior of welded EN AW 7020 was investigated. Exfoliation tests were performed according to the ASTM G34-01 standard. As expected, as a result of the tests, the base material region of all three samples were showed better corrosion resistance than the heat-affected region. Ultrasonic impact peening and two-step aging treatment was observed that improved EXCO sensitivity in the weld area. When sorting was made by considering the resistance to corrosion of the heat affected zone of the samples, it was observed that the best resistance was shown by the sample with two-step aging treatment, and the worst resistance was shown by the sample with T6 heat treatment.

Abstract The effect of two-step aging treatment on the fatigue behavior of welded AA 7020 Al. alloy was investigated. For fatigue tests to be carried out in atmospheric and seawater environments, a plane bending tester at a stress ratio of R = 0 was used. Experiments in the control group were carried out with unwelded specimens at a strain rate of R = −1 in air. The gradual heat treatment, two-step aging, significantly improved the fatigue and corrosion fatigue behavior of welded AA 7020 alloys. Unwelded specimens showed better fatigue properties than the welded ones. In the experiments in the seawater environment, pitting, and exfoliation corrosion occurred on the surfaces. It was determined that the corrosion pits reduce the fatigue life of welded and unwelded specimens. It was also observed that the corrosion sensitivity of the welded specimens increased in the heat affected zone and resulted in corrosion fatigue cracking.

Wire arc additive manufacturing (WAAM) is a metal additive manufacturing process which attracts significant attention in the manufacturing industry due to its ability to enable the production of the large components at a high deposition rate. However, high power input of the welding process causes complex heat transfer and thermal cycles which makes the WAAM process complicated. This paper presents the thermal behavior analysis of WAAM process which contributes the digital twin technology. A 3D thermal transient numerical simulation model is employed to investigate the temperature field evolution, heat input effect, temperature gradient and the effects of different cooling times on interlayer temperatures of single bead ten layer wall. The calculated temperature time diagrams and experimental measurements match well together. The results show that the heat dissipation becomes worse as the heat input increases with the same cooling time. The interlayer temperature increases 46 % percent with a doubled heat input. Temperature gradients decrease with the building height and higher heat input. Effect of different cooling time analysis show that interlayer temperatures could reach up to melting point with the building height.

Wire arc additive manufacturing (WAAM) which is literally based on continuously fed material deposition type of welding processes such as metal inert gas (MIG), tungsten inert gas (TIG) and plasma welding, is a variant of additive manufacturing technologies. WAAM steps forward with its high deposition rate and low equipment cost as compared to the powder feed and laser/electron beam heated processes among various additive manufacturing processes. In this work, sample parts made of low allow high strength steel (ER120S-G) was additively manufactured via WAAM method using robotic cold metal transfer technology (CMT). The process parameters and building strategies were investigated and correlated with the geometrical, metallurgical and mechanical properties on the produced wall geometries. The results obtained from the thin wall sample parts have showed that with increasing heat input, mechanical properties decreases, since higher heat accumulation and lower cooling rate increases the grain size. The tensile tests results have showed that casting steel (G24Mn6+QT2) mechanical properties which requires 500 MPa yield strength can be compared to with as build WAAM process having 640 MPa yield strength. Tensile strength were fulfilled for S690Q and yield strength is very close to the reference value.

Additive manufacturing (AM) is becoming increasingly popular since it offers flexibility to produce complex designs with less tooling and minimum material at shorter lead times. Wire arc additive manufacturing (WAAM) is a variant of additive manufacturing which allows economical production of large-scale and high-density parts. The WAAM process has been studied extensively on different steels; however, the influence of process parameters, specifically wire feed speed (WFS), travel speed (TS), and their ratio on bead geometry, microstructure, and mechanical properties, are yet to be studied. The present work aims at closing this gap by using the WAAM process with robotic cold metal transfer (CMT) technology to manufacture high-strength structural steel parts. For that purpose, single-bead welds were produced from HSLA steel by varying WFS between 5 and 10 m/min and the WFS to TS ratio between 10 and 20. Those variations produce heat inputs in the range of 266–619 J/mm. The results have shown that the wire feed speed to travel speed ratio is the major parameter to control the heat input. Increasing heat input increases characteristic bead dimension, whereas it reduces the hardness. In the second part of experiments, two single-bead walls were deposited via the parallel deposition strategy and one multiple-bead wall was produced using the oscillation strategy. The tensile properties were tested along two directions: parallel and perpendicular to deposition directions. For the yield strength and tensile strength, the difference between horizontally and vertically tested specimens was smaller than the standard deviations. On the other hand, the total and uniform elongation values exhibit up to 10% difference in the test direction, indicating anisotropy in ductility. Those tensile properties were attributed to repeated thermal cycles during the WAMM process, which can cause heat transfer in multiple directions. The yield strength of the multiple-bead wall produced via oscillation was lower, whereas its ductility was higher. The tensile properties and hardness differences were found to correlate well with the microstructure.

Due to increasing land / amphibious mobility and performance requirements, fatigue assessment plays a vital role in the design of armoured amphibious military ground vehicles. Fatigue assessment study can be divided into two main branches, which are the determination of vehicle loading spectrum and the determination of vehicle fatigue strength. FNSS Defense Systems initiated a project in order to further vehicle fatigue strength evaluation capabilities on the way to design more reliable and lighter vehicles. The project is called “Design and manufacturing methods improving fatigue strength of welded joints”, which is financially supported by TUBITAK. In this paper, the work accomplished and the results obtained in the framework of the project are presented. In this scope, fatigue test samples are manufactured from 5XXX series aluminium armour plate with the selected welded joints configurations. Post-weld fatigue improvement methods; TIG dressing, hammer peening and shot peening, are applied to test samples. Residual stress measurements on selected configurations are accomplished per X-Ray Diffraction technique to evaluate the effect of post-weld treatments on residual stresses, which is a major factor affecting fatigue life. Welding process is simulated with finite element method to be able to compute welding induced residual stresses. As input to simulations, temperature dependent thermo-mechanical and mechanical properties of utilized aluminium are determined on a forming dilatometer. Then as a crucial step in weld process simulation, weld process experiment is designed and conducted to calibrate welding process heat source and to verify simulation model. Finally, constant amplitude fatigue tests are conducted on an in-house designed and built four-point bending test machine. Test results are compared with the fatigue life calculated according to the IIW recommendations using various approaches and fatigue life computed with different techniques. As the outcomes of the project, FNSS weld class system is built highlighting the effect of post weld treatments, fatigue calculation procedures are enhanced and tuned accordingly, and substantial knowledge in weld process simulation is gained. Hence fatigue strength evaluation approach is evolved significantly.