Defect and Diffusion Forum Vol. 416

Abstract: An innovative method has been elaborated for the overlap friction stir welding (FSW) of 400 mm x 110 mm x 1 mm sheets of EN AW 5754 aluminium alloy, placed on a tilted jig.

Abstract: A welding test piece has been made by the overlap friction stir welding (FSW) of 400 mm x 110 mm x 1 mm sheets of EN AW 5754 aluminium alloy, placed on a tilted jig, of the multifunctional friction processing machine, type MMPF.

Abstract: Friction stir welding is an area of interest within ISIM Timisoara, several research projects that have addressed this issue being carried out. At ISIM the research started with the approach of FSW welding of some aluminum alloys (as similar and dissimilar materials) and later extended to other types of non-ferrous metallic materials (magnesium, titanium, copper alloys) and different types of steels respectively. New methods / possibilities of application of the FSW welding process were also researched. The paper presents results obtained by ISIM Timisoara within an ongoing national research project regarding the friction stir welding in inert gas environment (FSW-IG) of the AZ31B magnesium alloy. The experimental research aimed to perform a comparative analysis between the FSW-IG welding and the classic FSW welding for AZ31B magnesium alloy, in the same working conditions in terms of welding equipment, welding tools and technological process parameters. The obtained results show that the application of FSW-IG welding compared to the classic FSW welding brings benefits in terms of weld surface appearance, mechanical strength, elongation at break and behavior to the static bending tests.

Abstract: Due to their extraordinary qualities, X5CrNi18-10 (AISI 304L) and X3CrNiMo17-13-3 (AISI 316) stainless steels are among the most used materials in engineering applications with use in priority areas. This also involves finding new solutions for joining this type of metals, effective alternatives to the widely used conventional welding processes.The paper presents the approaches and results obtained at international level for the FSW welding of X5CrNi18-10 and X3CrNiMo17-13-3 stainless steels.The ISIM results are also presented for the FSW butt welding of X5CrNi18-10 stainless steel plates, 4.0 mm and 1.5 mm thick. Data regarding the materials to be welded, the characteristics of the welding tool and the technological process parameters are presented: the rotation speed of the welding tool and the welding speed.When monitoring the welding process, a method was used that is based on an innovative solution based on the use of the infrared thermographic technique, patented by ISIM Timisoara.When welding FSW in inert gas environment FSW-IG, an innovative technical solution for applying the method was used (submitted for patenting), a method that allows monitoring the process in the case of FSW-IG as well. The results of the evaluation process of the welded joints are also presented: referring to metallographic analyzes at macro and microscopic level, micro-hardness, tensile and bending tests.The very good results obtained internationally, but also those obtained at ISIM Timisoara, represent solid arguments that the FSW process can be applied with very good results for welding of X5CrNi18-10 and X3CrNiMo17-13-3 stainless steels.

Abstract: In this paperwork is presented a study of dissimilar welding with FCAW welding process, between duplex stainless steel S31803 (1.4462) and naval carbon steel EH36 (1.0546), being analyzed all the considerations related to their weldability, resulted mechanical properties, microstructure and evaluation of the toughness and hardness of the weld seam and HAZ area.

Abstract: The aim of the current study is to perform a failure analysis on specimens extracted from 4 mm sheets of AZ31B, according to ASTM 4377G and 3 mm sheets of Cu99 alloys according to SR EN 1652:2000, that were joined together using FSW and FSW-IG processes. In order to promote the suitability and advantages of implementing FSW-IG processes in the automotive and aerospace industry, the papers authors performed destructive testing on the samples extracted, namely tensile strength test, following with topography analysis using scanning electron microscopy – SEM, combined with energy dispersive spectroscopy EDS, micro-hardness tests and fractography investigations. Results highlighted a considerable improvement in the ultimate tensile strength of the welded joint, a higher degree of deformability of the welded joint in the case of FSW – IG, compared to classical FSW; while maintaining the same process conditions and parameters. Experimental data is in accordant with automotive and aerospace imposed compliances, thus presented and discussed in the following scientific article.

Abstract: In this paper, two numerical models of friction stir welding of two aluminum plates are considered. The coupled mechanical-temperature problem is solved with explicit integration over the time. The two models are based on the finite elements method (FEM) and have different complexity and number of participating parameters. The aim of the development is to highlight the weaknesses and strengths of the models of different complexity. The first model is simpler and it is based on the free penetration of the tool into the parts. The second model is based on the arbitrary Lagrange-Euler method and take in to the account the instrument penetration that allows to take into account the movement of the material in the process area. Convective and radiative heat transfers are accounted in the two models. The results for the temperature, stress and strain in the welded joint are studied and compared. The calculation time is given for each model. A parametric analysis was performed for the influence of the rotational speed of the pin, welding velocity and the pressing force. The influence of the temperature dependent physical properties of the welded plates is determined and compared for the both finite element models.

Abstract: Many of the features and advantages of TIG welding are well known. The paper presents in part the results of some experimental research using TIG welding with high frequency pulsed arc. A comparative study was performed between the application of TIG welding with high frequency pulsed arc technology and classical TIG welding, applied to achieve welded joints of stainless-steel parts. The conclusions are based both on the characteristics of the welding process (the hole main group of parameters) and the results of the applied non-destructive and destructive testing methods. Features like reduced deformations in the joint, low energy guaranteed ignition, wonderful focalization of the high current density arc, increased working speed and not the last, the special look of the welded plates recommends this procedure for some replacement possibilities for the expensive laser welding process. Aspects of improving the quality of welded joints are highlighted, given the low manufacturing costs.

Abstract: Titanium (Ti) is highly valued for its strength-to-weight ratio and corrosion resistance. However, after it is processed to a wrought, or shaped form, it is typically in excess of 40 times more expensive than the corresponding steel part and nearly 20 times more expensive than the aluminum part. The high production costs of titanium in comparison to other structural metals is the main limiting factor for the wide employment of titanium. Cost reduction can be addressed considering creative fabrication methods and/or formulating new chemical compositions. In general, low-cost technology of titanium alloy can be implemented from raw material, alloy design and processing and forming. The core idea of low-cost titanium alloy design is to use cheap alloying elements to instead of expensive alloying elements without reducing the performance of the alloy. Iron has been considered for the development of few low-cost titanium alloys because of its stabilizing effect of the β-phase. Besides, it has a large solid solubility in β-Ti and owing to the atomic size difference with Ti can enable significant solution strengthening. But due to the high density of iron, high quantity of β-stabilizing elements and the formation of TiFe-based brittle intermetallic phases, welding joints of low-cost titanium alloys are prone to formation of cold cracks which is very important limiting factor for obtaining high quality welded joints with a strength of at least 90% compared to the strength of base material. Electron Beam Welding with its higher welding speed and intensity, can prevent formation of intermetallic and could help in obtaining welds with better mechanical properties, especially in combination with either pre-or post-welding heat treatment. The aim of this work is to study the effect of pre-heating and post-welding heat treatment on low-cost β-titanium alloy Ti-2.8Al-5.1Mo-4.9Fe welding joints by performing electron beam welding in combination with pre-and post-welding heat treatment. Specifically, this work will help to understand the influence of such techniques on the structure, phase composition and mechanical properties of low-cost β-titanium alloy welded joint.

Abstract: The need for welded structures of high-strength steels requires detailed studies on the factors influencing the behaviour of these steels during welding. The present work introduces results on the influence of the welding gap on the structure and some mechanical and technological properties of welded joints of high-strength steel S960QL, joined by submerged arc welding.