Mechanical properties, microstructure and crystallographic texture of magnesium AZ91-D alloy welded by Friction Stir Welding (FSW)

The objective of the study was to characterize the properties of a magnesium alloy welded by friction stir welding (FSW). The results led to a better understanding of the relationship between this process and the microstructure and anisotropic properties of alloy materials. Welding principally leads to a large reduction in grain size in welded zones due to the phenomenon of dynamic recrystallization. The most remarkable observation was that crystallographic textures appeared from a base metal without texture in two zones: the thermo-mechanically affected and stir welded zones. The latter zone has the peculiarity of possessing a marked texture with two components on the basal plane and the pyramidal plane. These characteristics disappeared in the TMAZ, which had only one component following the basal plane. These modifications have been explained by the nature of the plastic deformation in these zones, which occurs at a moderate temperature in the TMAZ and high temperature in the SWZ

LASERS AND THE PROCESSING OF ENGINEERING MATERIALS

The developments in the surface treatment of materials are reviewed. There are several possible forms laser surface treatment can take viz : a) Transformation hardening heating a steel to produce austenite which on the subsequent self quenchin transforms to martensite b) Surface melting simply melting a surface layer c) Surface alloying melting a surface layer and simultaneously changing the composition to achieve the desired properties d) Cladding coating the surface with hard metal particles or with an alloy different from the substrate e) Ceramic coating laser melting, sealing of ceramic coatings f) Amorphous layers coating the surface with an alloy which on cooling solidifies in an amorphous state

LASER MELTING OF PLASMA SPRAYED CERAMIC COATINGS

The porosity in the plasma sprayed ceramic coatings limits its life in many applications. A viable approach to overcome this problem is to remelt the coating using a laser beam. The melted layer cools non-uniformaly and the resulting tensile stresses generally lead to cracking. In this investigation, laser melting of ZrO2Al2O3 and TiO2 coatings was carried out. Laser operating parameters were optimized to obtain melted layers with as few cracks as possible. The conditions that lead to complete elimination of cracks have been identified and successfully demonstrated for Al2O3 and TiO2 coatings

Praezisionsbearbeitung mit Festkoerperlasern: Fuegen. Teilprojekt: Schweissen von Werkstoffen bzw. Werkstoffkombinationen mit geringer Schweissneigung Abschlussbericht

The aim of this project was to evaluate the weldability of materials which are difficult to joint by conventional methods using a pulsed Nd:YAG laser. Because high strength aluminium alloys found increased interest for applications in the automobile and aircraft industry the research was focussed on the welding of the age hardenable alloys AlMgSi1, AlCuMg1 and AlZnMgCu1,5. Welding was conducted with and without filter. Only for the alloy AlZnMgCu1,5 the use of a filler was essential to achieve a good joint. The tensile strength of AlMgSi1 joints reached 64% of the value for the base material thus exceeding the tensile strength of TIG- and WIG-welded joints. With a subsequent heat treatment (solutionizing and age hardening) the tensile strength was increased up to 71%. For the alloy AlCuMg1 values of 61 and 86% respectively were achieved. Welding with filler led to a further increase of the tensile strength (approximately 10% compared to the values of joints welded without filler). For AlMgSi1 an AlSi12 filler was best whereas for AlCuMg1 and AlZnMgCu1,5 the addition of AlMg5 led to better results. The fatigue strength of AlMgSi1 and AlCuMg1 joints drops to values 40 to 60% below those of the base material. Considering that the joints were tested in the as-welded condition this decrease is not dramatical. Moreover, the variance is low. However, the AlZnMgCu1,5 joints were notch-sensitive and due to an extreme variance no Woehler curve could be determined. Therefore Nd:YAG laser welded joints of this alloy cannot be recommended for applications were fatigue resistance is required. (orig.)SIGLEAvailable from TIB Hannover: F99B841+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman