Modification of Materials Local Properties by Friction Stir Processing

Friction stir processing (FSP) is a new solid state processing technique that can eliminate casting defects and refine microstructures, enhancing formability and improving other properties. FSP can also produce fine-grained microstructures through thickness. Essentially, FSP is a local thermo-mechanical metal working process that changes the local properties without influencing the properties of the bulk material. Firstly, the paper introduces FSP fundamental parameters, as advancing and rotating tool speed, approaching their influence on the processed surface roughness of Al6061. Single and overlapped friction stir processed layers were considered for the roughness analysis. Roughness mapping revealed existence of transitory and quasi-stationary phases of FSP. A process monitoring method obtaining through roughness control is envisaged. The paper also presents the material flow, microstructure and hardness in case of aluminium processed by FSP

Quality Of The Vocational Training For Construction Inspectors

The paper addresses the quality of the continuing training and vocational education for the construction inspector job and the harmonized European recognition of this qualification. It is the result of a survey realized in 5 EU countries (Greece, Hungary, Poland, Portugal and Romania) within the fame of the project entitled “Analysis and Comparative Study on construction inspection job performance regulations. European comparative study – KNOWLEDGE”. The general objective was to give recommendations for improving the qualification of civil construction inspectors by identifying the gap between the existing vocational education / training systems, and people/companies’ expectations and needs, as resulted from current literature, in-depth interviews and questionnaire surveys. The conclusions are related to the necessity of developing a training/certification program for the construction inspector, the magnitude and European dimension of such training and certification program, and the thematic areas that the program will cover to meet the construction industry requirements. Courses approaching New Construction Materials, Quality Control Procedures, Legislation on Town Planning, Private Constructions and Public Works, Legislation on Safety Issues in the Construction Industry, and the EU directives were identified as being necessary for updating the knowledge of the construction inspectors. Relevant graphs presenting the continuing training needs of the construction inspectors resulted from the in-depth interviews are presented. It results as a LLL European policy requisite the development of a European Certification for construction inspector

Welding in solid state

The importance of the Solid State Processes (SSP) has increased in the last decade due to the industry demands of improved properties of joined/surfaced materials, combined with cost reduction and energy saving. New and/or micro-scale solid state processed materials are used by aerospace, automotive and electrotechnics industry. Nowadays, classic SSP are mainly applied to light materials, but progresses were also reported in steels. In this field, the tools design, the technology and practical techniques surpassed the fundamental approach of the materials solid state processing. The SSP parameters evaluation is based on different experiments, approaching the material flow in the large plastic deformation domain. The paper approaches the solid state welding/joining and surface processing. The envisaged SSP are solid state joining processes as Cold Welding (butt and spot welding), Friction Stir Welding – FSW, and surface processing, Friction Stir Processing - FSP. Therefore, the investigation targeted the deformation and flow pattern of the parent metal in case of cold welding and FSW/FSP, processes parameters evaluation and correlation, local analysis of the material structural transformations, and material hardening

Thermal influence of welding process on strength overmatching of thin dissimilar sheets joints

The investigation addresses the overall performance of black and white joints (BWJ) of low carbon steel and stainless steel thin sheets achieved by laser hybrid welding. First, thermal field modelling is carried out by considering Goldak’s double ellipsoidal heat source model, together with a contribution of the authors related to the shape coefficients. In parallel, the technological development of BWJ laser hybrid welding is also addressed. Material characterisation by means of macro and microstructural examination and hardness tests is performed. The overall tensile performance of BWJ is discussed together with the weld metal strength overmatching. The tensile tests results indicate that in case of transversally loaded joints, the positive difference in yield between the weld metal and the base materials protects the weld metal from being plastically deformed; the flat transverse tensile specimens loading up to failure reveals large strains in low carbon steel, far away from the wel

Arc welding of Dissimilar Metals:FEA and Experiments

Assuming an elliptical disk heat source, several results of theoretical and experimental investigations on heat transfer in copper - low carbon steel welded joints are presented in the first part of the paper. Using thin sheets, temperature variation in the thickness direction is negligible and heat flow is considered two-dimensional. Convection and radiation influence, and thermo-physical properties depending on the temperature are considered in the model. Measurements and visualization of the temperatures distribution have been made during welding using infrared thermography. The proposed theoretical method using finite element analysis was validated for the temperatures prediction in the welded joint. In the second part of the paper, the influence of the welding process on the structural modifications and grains’ size in the heat affected zone (HAZ) of both base materials (BM) is described. Discussion on the graphs of temperatures variation vs. microstructural analysis enables conclusions on the potential undesired structural changes and related preventing measures. The asymmetric position of the heat source closer to the material having a higher thermal conductivity is an effective method for controlling the temperature field

Cold welding on cogged surface

La soldadura por frío entre superficies dentadas es lograda presionando una chapa de aluminio deformable fácilmente por una superficie dentada de un componente más duro. El proceso requiere la limpieza exacta de las chapas en el área de contacto. El empalme se logra solamente por grande deformación plástica del componente del aluminio, que entra entre los dientes del más duro, hecha de cobre, o de acero carbón o inoxidable. El papel presenta el modelo 2D por elemento finito del proceso: Los resultados como tensión elemental y las tensiones en el área de contacto en el componente de aluminio fueron discutidos y comparados con experimentos. Se presentan también la deformación y/o las grietas del aluminio que fluye durante presionar entre los dientes del material más duro, a diversas grados de deformación. El uso industrial más importante del proceso es en electrotécnica, para los empalmes disímiles de aluminio-cobre.-Cold welding on cogged surfaces is achieved by pressing an easy deformable sheet of aluminium on a cogged surface of a harder component. The process requires sheets accurate cleaning in the contact area, where the cold welding is expected to occur. The joint was obtained only by large plastic deformation of the aluminium component on the harder one, made from copper, or carbon/stainless steel. The paper presents the 2D Finite Element Method Model of the process; results as aluminium component elementary strain and stresses in the contact area were discussed and compared with experiments. The aluminium flowing during pressing into the harder material cogs at different deformations, its deformation or cracking are presented, as too. The process industrial application in electrotechnics, to obtaining dissimilar joints of aluminium-copper, is of high importance due to the coupled materials electric properties

New Approach on the Cold Welding of Metals: Application to Aluminium Bars

La soldadura por frío por presión es un proceso de fabricación de empalme en estado sólido con varios usos importantes, pero carente en sus fundamentales. Este papel presenta un nuevo acercamiento de la investigación en el campo, trayendo contribuciones originales teóricas y prácticas al conocimiento del principio de la soldadura en frío y creando las bases para el desarrollo de los nuevos procesos que tratan los materiales modernos. El acercamiento se basa en un FEM capaz para predecir el comportamiento material durante la deformación, considerando varias condiciones introducidos por el código usado: análisis estático no linear, tensión grande y desviación grande, dislocaciones prescritas. La correlación entre las tensiones y la deformación del material ha sido tratada luego. Las dimensiones y las características de la zona afectada mecánica - MAZ (desarrollado en el material debido al proceso de deformación) están también alcanzados.-Cold pressure welding is a solid state joining manufacturing process with several important applications, but with gaps in its fundamentals. This paper presents a new approach of the research in the field, bringing both theoretical and practical original contributions to the knowledge of the cold welding principle and creating the bases for the development of new processes addressing modern materials. The approach is based on a FEM capable to predict the material behaviour during the up-setting, considering several constrains introduced by the used FEA code: non-linear static analysis, large strain and large deflection, prescribed displacements. Correlation between stresses and material deformation is further addressed. The dimensions and characteristics of the Mechanical Affected Zone – MAZ (developed in the material due to the up-setting process) are identified

Residual stress analysis of friction stir processed AA6061

Currently, after appropriate heat treatments, the 6xxx aluminium alloys are used in a variety of applications including aircraft fuselage skins and automobile body panels and bumpers, instead of more expensive 2xxx or 7xxx alloys. The paper presents the results of the residual stress analysis in case of Friction Stir Processing - FSP of AA6061-T4 plates, 10 mm thickness, demonstrating the process ability to locally modify the base metal properties. The residual stresses, DRX depicted, are correlated with the microstructure and hardness results

Strain-Hardness Correlation in Aluminium Butt Cold Welded Joints

Butt cold welding is a solid phase welding process where welding occurs by plastic deformation of the metals to be welded. It is obtained by cold pressing until the expansion of the contact zone of the two parts creates contaminant-free areas, allowing the contact and creation of a common lattice between the opposing clean surfaces. Consequently, butt cold pressure welding raises interesting theoretical and practical issues related to the material large plastic deformation, and its consequent hardening. The method used to determine the 99.5%Al hardness-strain correlation is based on Vickers micro-hardness HV0.5 test results on upset bars at different values of effective strain. Two approximations of the relationship between hardness and the effective strain were determined, namely as a rational function, and as a power function. These functions were used for validating an original FEM model of 99.5% Al bar butt cold welding

Soldadura láser remota de aceros de alto límite elástico

En este artículo se presenta un estudio de soldabilidad del acero de alto límite elástico Usibor 1500 P revestido al Al-Si sin tratar térmicamente mediante soldadura láser remota. La soldadura de este material presenta dificultades debido a que el Al presente en el recubrimiento provoca inclusiones de compuestos íntermetálicos Al-Fe en la unión. Estos compuestos tienen baja ductilidad y fractura frágil a temperatura ambiente, produciendo estos efectos en la unión realizada.- This paper presents a weldability study of Usibor 1500 P high strength steel pre-coated of Al-Si in the non quenched state by remote laser welding. The pollution of the melt pool by Al-Fe intermetallic particles during laser welding results in low strength joints