Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Solidification of GTA aluminum weld metal: Part 1 - Grain morphology dependent upon alloy composition and grain refiner content
    ( 2014)
    Schempp, P.
    ;
    Cross, C.E.
    ;
    Pittner, A.
    ;
    Oder, G.
    ;
    Neumann, R.S.
    ;
    Rooch, H.
    ;
    Dörfel, I.
    ;
    Österle, W.
    ;
    Rethmeier, M.
    The solidification conditions during welding strongly influence the weld metal microstructure and mechanical properties of a weld. In the first part of this study, the grain morphology of gas tungsten arc (GTA) bead-on-plate welds was investigated for the aluminum Alloys 1050A (Al 99.5), 6082 (Al Si1MgMn), and 5083 (Al Mg4,5Mn0.7). The experiments revealed that increasing welding speed and alloy content allow the growth of small, equiaxed grains, particularly in the weld center. Furthermore, increasing grain refiner additions led to a strong reduction of the weld metal mean grain size and hence facilitated the columnar to equiaxed transition (CET). In addition, wavelength dispersive X-ray spectroscopy (WDS) and transmission electron microscopy (TEM) analysis revealed in the weld metal TiB2 particles that were surrounded by Al3Ti. This suggests the duplex nucleation theory for nucleation of aluminum grains in GTA weld metal.
  • Publication
    Influence of grain size on mechanical properties of aluminium GTA weld metal
    ( 2013)
    Schempp, P.
    ;
    Cross, C.E.
    ;
    Häcker, R.
    ;
    Pittner, A.
    ;
    Rethmeier, M.
    Grain refinement is an important possibility to enhance the mechanical properties such as strength, ductility and toughness of aluminium weld metal. In this study, grain refinement was achieved through the addition of commercial grain refiner Al Ti5B1 to gas tungsten arc weld metal of the aluminium alloys 1050A (Al 99.5) and 5083 (Al Mg4.5Mn0.7). The grain refiner additions led to a significant reduction of the weld metal mean grain size (Alloy 1050A, 86 %; Alloy 5083, 44 %) with a change in grain shape from columnar to equiaxed. Tensile tests showed for Alloy 5083 that the weld metal's ductility can be increased through grain refinement. No improvement in weld metal strength (i.e. yield strength and ultimate tensile strength) was observed. Furthermore, tear tests with notched specimens revealed that the resistance against initiation and propagation of cracks in the weld metal can be enhanced through grain refinement. The toughness was observed to increase clearly by grain refinement in weld metal of commercial pure Al (Alloy 1050A). In Alloy 5083 weld metal, the toughness was not improved through grain refinement, likely because of a semi-continuous network of brittle intermetallic phases that facilitate crack propagation.