Key Engineering Materials Vol. 890

Abstract: Throughout the history of modernization of welding processes, in many cases the research has focused on optimizing the location of energy in the welding area, with the continuous improvement of the quality of welded joints. The welding processes in shielding gas environment with fusible electrode (MIG-MAG) have achieved superior performances regarding the increase of the current density around of the welded joint, simultaneously with the increase of the universality degree of their application. This paper is based on researching the possibilities of concentrating energy in the welding area, seeking to obtain both more favorable energy yields and an increased quality of welded joints. In the paper are shown a some results obtained following a comparative study on 2 welding processes in MIG-MAG protective gas medium, differentiated mainly by the metal drop transfer mode: by spraying (Spray arc), respectively by synergistic transfer (Arc pulsed), applied for corner welding of alloy steel sheets.

Abstract: Replacing worn or damaged parts implies high material costs and financial expense for public tram transportation services, especially for the imported units and that is why it is preferable to recondition them, taking into consideration the safety requirements. In this paper, ISIM initiatives and achievements are presented in the field of cost reduction and maintenance during operation of trams, by introduction in the operation process of worn parts, within the safety limits. Aspects are presented regarding the possibilities for reconditioning and repair of parts with a circular geometry (e.g. wheel bands, axles, drum brakes). Some of these are being applied and implemented. Also, innovative ideas are presented for increasing the performance of equipment used for reconditioning.

Abstract: Reproducibility in respect to welded structures realization is one of the main requirements for a wide variety of industrial applications. One of the international tendencies regarding the use of the steel is the replacing, in critical areas, of structural steels with high performance steel, e.g. with HSLA steels. The paper presents the results of a factorial designed experimental program focused on determining mathematical correlations between the GMAW process parameters for T joints of 4mm thick steel plates of structural (S235JR+AR according to SR EN 10025-2) and hot-rolled, high-strength low-alloy (HSLA) steel plates (S420MC according to EN 10025-4), respectively. A comparison between the obtained mathematical correlations that connect the welding parameters and the main mechanical characteristics is presented. The correlations can be used for applying the optimal combination of welding process parameters for realizing the T-joints of welded products.

Abstract: In all industrial fields, the product requirements are more and more demanding. HSLA steels are designed to provide higher atmospheric corrosion resistance and improved mechanical properties than structural steels. The paper presents the results of an experimental program based on factorial design, applied to predict the mechanical properties of butt-welded joints of S420MC and S460MC hot-rolled, high-strength low-alloy (HSLA) steel plates with 2mm, 4mm and 8mm thickness. Gas Metal Arc Welding (GMAW) was used and correlations between the main process parameters and the related mechanical properties of the welded joints were found. Obtained mathematical correlations can be exploited to provide optimal combination of welding parameters to fit the quality requirements of the end-users for envisaged welded product.

Abstract: In the automotive industry there is an increasing demand for the wider application of high strength steels due to their favourable mechanical properties. The steel producers continuously developing new generations of high strength steels to insure higher strength and toughness properties. Since in most cases these steels are joined in welded structures, great attention must be taken to their weldability. The weldability of high strength steels has still challenges which are as follows: cold cracking sensitivity; reduction of strength and toughness of heat affected zone (HAZ); filler metal selection. Because the mechanical properties of ultrahigh strength steels are provided by using various alloying elements, micro alloys, and by different metallurgical methods, the steels may lose their outstanding properties during welding. In real welded joints the critical parts of the HAZ have small extent so their properties can be limitedly analysed by conventional material testing methods. With the help of physical simulators, the different parts of the heat affected zone can be produced in an adequate size for subsequent tests. In our research work the weldability, especially the HAZ properties of an ultrahigh strength structural steel (R_p0.2 = 1300 MPa) were investigated on thermal simulated samples with the help of Gleeble 3500 physical simulator. Three relevant technological variants for gas metal arc welding (GMAW), t_8/5 = 5 s, 15 s and 30 s were applied during the HAZ simulations in the selected coarse-grained (CGHAZ), intercritical (ICHAZ) and intercritically reheated coarse-grained (ICCGHAZ) zones. Both the microstructure was studied by optical microscope and the mechanical properties were analysed by Vickers hardness tests and Charpy V-notch impact tests at -40 °C. According to the results the investigated ultrahigh strength steel was softened on account of the welding heat cycles, besides that the strength of the investigated ultrahigh strength steel can be better with the application of shorter t_8/5 cooling time.

Abstract: The friction processing techniques, respectively those that use ultrasonic waves, have been for several years important research directions for ISIM Timisoara. The remarkable scientific results obtained through the development of complex research programs for these processes, the diversification of the application possibilities, the desire to improve the characteristics of welded joints, were the basis of the development of the US-assisted FSW hybrid welding process. The paper presents the results obtained by ISIM Timișoara regarding the development of the FSW-US hybrid joining process. Variants of original technical solutions for the necessary equipment are presented together with assessments regarding the conditions of application of the FSW-US process. Experimental results are also presented for FSW-US welding for pairs of materials such as aluminum alloys EN AW 5754 and EN AW 1200, respectively steel EN 10111 DD13. Comparative assessments are made between classic FSW welding and FSW-US hybrid welding, which highlight the advantages of applying the hybrid process.

Abstract: The results obtained by ISIM Timisoara to the development of the friction stir welding process (FSW) have supported the extension of the researches on some derived processes, including friction stir processing (FSP). The experimental programs (the researches) were developed within complex research projects, aspects regarding the principle of the process, modalities and techniques of application, experiments for specific applications, being approached. The paper presents good results obtained by friction stir processing of cast aluminum alloys and copper alloys. The optimal process conditions, optimal characteristics of the processing tools were defined. The complex characterization of the processed areas was done, the advantages of the process applying being presented, especially for the cast aluminum alloys: EN AW 4047, EN AW 5083 and EN AW 7021. The characteristics of the processed areas are compared with those of the base materials. The results obtained are a solid basis for substantiating of some specific industrial applications, especially in the automotive, aeronautical / aerospace fields.

Abstract: Considering the remarkable results obtained by using friction stir welding process (FSW), ISIM Timisoara has developed research programs for the knowledge and development of processing processes based on the FSW process principle.The paper presents a synthesis of the researches and the results obtained within some of research projects carried out by ISIM Timisoara, regarding possibilities of using some of processes derived from the FSW process, which has focused mainly on two directions (areas): surface engineering (materials surface processing) and joining by friction riveting. In the field of surfaces engineering, there are presented some results that represent own contributions of ISIM Timisoara, regarding: friction stir processing as well as coating with functional layers from lightweight alloys of steel substrates (by friction with consumable tool).Regarding friction riveting, two methods are presented: classic friction riveting, respectively friction riveting with hybrid effect (mechanical grip and friction welding).The paper shows very good results obtained to FSP processing (for cast aluminum alloys), to friction riveting with hybrid effect (for aluminum and copper alloys) and to friction riveting (for aluminum alloy), but also some limitations of these friction processing methods.Also in the paper are presented new research directions that are currently being addressed, respectively that will be addressed in the next period at ISIM Timisoara, regarding new variants of application of FSW welding.

Abstract: Due to their properties (low density, high corrosion resistance, easy to process), magnesium alloys are used in all important industrial fields (aeronautics, automotive, transport, etc.). Magnesium is the lightest metal for complex metal structures with a density 2-3 times lower than that of aluminum and a quarter than that of steel. The possibility of joining magnesium with other materials allows a greater flexibility in designing and increasing the number of applications for light alloys.This paper presents results obtained by ISIM Timisoara for FSW welding of magnesium alloy AZ31B. Considering the difficulties that arise when welding magnesium alloys using classical processes, it can be assumed that by applying the FSW process for joining these types of materials, the results obtained are very good and can substantiate industrial applications.