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Zupanc U.,Welding Institute | Grum J.,University of Ljubljana
Journal of Materials Processing Technology | Year: 2010

Pitting corrosion has a major influence on aging of structural elements made of high-strength aluminium alloys as corrosion pits lead to earlier fatigue crack initiation under tensile dynamic loading. A cause of fatigue crack initiation in a corrosive medium is a stress concentration at a corroded area. In order to improve material resistance to corrosion fatigue it is necessary to reduce pit-tip stresses. To eliminate or reduce pit stresses, cold surface hardening by shot peening was proposed. The objective of the present study was to investigate the effect of surface hardening by shot peening on electrochemical stability and corrosion fatigue properties of high-strength aluminium alloy 7075-T651 in the corrosive environment of a chloride solution. The results obtained show a favourable influence of shot-peening treatment on corrosion fatigue properties. Induced compressive residual stresses in the surface layer retard the initiation of fatigue cracks, and so the fatigue life improvement of structural elements made of high-strength aluminium alloys was observed. © 2010 Elsevier B.V. All rights reserved.

Slazak B.,Lincoln Electrical Bester | Slania J.,Welding Institute | Wegrzyn T.,WSZOP | Silva A.P.,University of Beira Interior
Materials Science Forum | Year: 2013

The experimental investigation has been carried out to evaluate process stability for two rutile types of electrode supplied with two types of DC power sources: traditional 3 phase thyristor and inverter type. Initially to understand the maximum range of outcomes high quality and defective electrodes, with lower arc stability, were selected for both. During welding tests current and voltage signals were recorded separately with the aid of A/D converter and 5 kHz of sampling frequency. On the basis of digital signals obtained from each electrode type and power sources, a number of statistical indicators have been computed. Furthermore voltage and current histograms have been determined (defined as a density distribution of welding arc voltage and current values). Statistical indicators of voltage signals have proved to be more useful for process stability evaluation, particularly mean voltage (Usśr) and histograms as well as voltage coefficient of variation (Kvu). © (2013) Trans Tech Publications, Switzerland.

This article contains an analysis of the effect of two electrode force systems (pneumatic and servomechanical) on the formation of a projection weld. Calculations and experiments were conducted on steel DX53 (a 1.5-mm-Thick test plate with an embossed projection) and for various values of electrode force (pneumatic system) and electrode travel (servomechanical system). The comparative analysis of the systems was performed using finite element method (FEM) calculations (SORPAS∗ software) and experimental verification. The research also involved destructive and nondestructive examinations (peeling and static tensile tests, plus metallographic examinations). The analysis included the space distribution of volumetric power density in the projection material to determine the heating efficiency of both electrode force systems. The presented method of force and travel of electrodes during projection welding was entirely different from methods used previously and changed the existing views on projection welding. The new solution consisted of applying a hybrid servomechanical force system for controlling both electrode force and electrode travel (force is controlled before and after the flow of current, whereas travel is controlled during the flow of current). The force applied before the flow of welding current was lower than the force exerted by the classical i.e., pneumatic force system. The main advantages of this solution were the following: 1) a smaller cold projection height reduction, 2) a smaller area of contact between materials being welded, and 3) melting of the projection material was initiated in the projection cap. All these three advantages enable the prevention of the formation of an undesirable ring weld at the beginning of a welding process. This solution makes it possible to extend a projection height reduction time (several times) and generate greater energy in the projection during the projection height reduction.

The application of low-energy methods of metal inert gas welding (ColdArc and CMT) for the manufacture of joints in hard-weldable aluminium alloys is presented. The purpose of the technological research was to show the usefulness of the CMT and ColdArc methods for production of butt and T-joints in 2.0 mm thick aluminium alloy plates. Basic difficulties related to welding of 6xxx and 2xxx series aluminium alloys and the specificity of welding by low-energy methods are discussed. Selected results of metallographic macro- and microscopic examination as well as those of tensile and bend tests are given; detailed analysis of the results is also carried out. The article shows also that ColdArc and CMT methods provide high quality and aesthetic welded joints in aluminium alloys that are considered to be non-weldable or of limited weldability. © 2014 © 2012 Taylor & Francis.

St. Weglowski M.,Welding Institute
Welding International | Year: 2014

We present a new technology of friction stir modification of material top layers. This technology is derived from that of friction stir welding. On the basis of a literature survey, the following is described: equipment, tools, advantages, and possible applications of FSP technology. It is found that the technology should gain recognition in Polish industry, which is more and more interested in implementation of advanced technologies. © 2013 Taylor & Francis.

Differences in the nature of the thermal cycle run under welding conditions in comparison to that during conventional heat treatment are shown. The methods of investigations into microstructural changes of austenite under welding thermal cycles conditions developed and used at the Welding Institute in Gliwice are discussed. The investigation results, in the form of CTPC-S diagrams for construction steels of grades X12CrCoWVNbl 2-2-2 (VM12-SHC), 7CrMoVTiB10-10 (P24) and 10CrMo9-10 (P22), are presented and compared with those in the form of CTPC diagrams plotted for metallurgical conditions. © 2013 © 2013 Taylor & Francis.

Pasek-Siurek H.,Welding Institute
Welding International | Year: 2014

We present advantages of plasma arc welding in relation to the other welding technologies, methods of plasma welding as well as the operation manner and design of plasma welding equipment. © 2013 Taylor & Francis.

Dworak J.,Welding Institute
Welding International | Year: 2014

We present the general characteristics of laser welding technology with the use of the radiation beam emitted in the pulse mode. The relationships between energy parameters of the pulse radiation beam are. We show that the pulse shape (i.e. defined course of power changes during pulse endurance) is one of the laser beam parameters affecting the welding process course, especially that in which thin precise elements are involved. By means of demonstration melting and welded joints of selected materials, the possibility of changing the weld shape and the manner of the weld metal crystallization through the application of different shape laser beam pulses is illustrated. © 2013 © 2013 Taylor & Francis.

Gola B.,Welding Institute
Welding International | Year: 2014

The purpose of liquid-penetrant inspection of metallic structures of historic value is the assessment of their technical state and suitability for further operational use. In this paper, the flaws of metal structures detected by means of penetrant inspection, conditions under which inspection can be made, requirements for inspection personnel, liquid-penetrant sets, measuring and auxiliary equipment and the inspection course are discussed. As an example, the results of inspection of a section of the riveted structure of an antique workshop roof are presented. © 2014 Taylor & Francis.

Zorc B.,Welding Institute
Revista de Metalurgia (Madrid) | Year: 2011

The paper treats studies of TIG gas-shielded arc welding using pure nitrogen, N2+ 5-20 % Ar gas mixtures and N2 + 2-10 % H2 gas mixtures. A weld root shielding was provided by nitrogen gas. Welding in N2 requires by 40 % lower welding current than welding in argon. The study showed that porosity was an issue due to overalloying of N2 in the weld pool; it can, however, be avoided with adequate welding parameters, particularly sufficiently high welding speed and controlled low heat input. The microstructure of all-weld metal is fully austenitic (γ). Hydrogen reduces nitrogen solubility in the weld pool and produces an austenitic-ferritic (γ+δ) microstructure. Titanium increases nitrogen solubility in the weld pool and strongly reacts with nitrogen. Consequently, there is a high fraction of TiN inclusions in the weld metal.

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