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Influence of welding speed and grain refinement on grain morphology in aluminium GTA weld metal
(2012)
Grain refinement is an important possibility to enhance the weldability of aluminium weld metal that is usually defined by its susceptibility to solidification cracking. In this study, grain refinement was achieved through the addition of commercial grain refiner containing titanium and boron to the GTA weld metal of aluminium alloy 6082. The weld metal mean grain size could be reduced significantly from about 70 µm to a saturated size of 21 µm with a change in grain shape from columnar to equiaxed. The grain refinement prevented the formation of centreline solidification cracking that was present only in welds with unrefined grain structure. A variation of torch speed led to a strong change of solidification parameters such as cooling rate that was measured in the weld metal and the corresponding solidification rate and thermal gradient. The ratio thermal gradient/growth rate (G/R) decreased from 50 K s/mm² (high torch speed) to 10 K s/mm² (low torch speed). However, the variation of torch speed did not change the tendency for solidification cracking. The microstructure of unrefined and completely refined weld metal was compared. The observed change in size and distribution of the interdendritic phases was related to the change in susceptibility to solidification cracking.
The microstructure of a fusion weld has great influences on the susceptibility of the base material to hot cracking and on the mechanical properties of the weld. Small, globulitic grains are necessary for increased strength, ductility and toughness and for a low inclination to hot cracking instead of large, oblong grains. This study reports on the factors which exert the main influences on such grain refinement in the weld. Thus, the influences of the thermal conditions, the chemical composition of the weld metal and the number and type of solidification nuclei on the microstructure were classified for the TIG welding of three different aluminium alloys.
Die Mikrostruktur einer Schmelzschweißnaht hat großen Einfluss auf die Heißrissanfälligkeit des Grundwerkstoffs und die mechanischen Eigenschaften der Schweißnaht. Für eine erhöhte Festigkeit, Duktilität und Zähigkeit und eine geringe Heißrissneigung sind anstatt großer, länglicher Körner kleine, globulitische Körner notwendig. Diese Studie berichtet über die Faktoren, die eine solche Schweißnahtkornfeinung hauptsächlich beeinflussen. So wurde für das Wolfram-Intertgasschweißen (WIG-Schweißen) von drei verschiedenen Aluminiumlegierungen der Einfluss der thermischen Bedingungen, der chemischen Zusammensetzung des Schweißguts und der Anzahl und Art der Erstarrungskeime auf die Mikrostruktur klassifiziert.---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
The microstructure of fusion welds has a significant influence on the susceptibility of the base material to hot cracking and on the mechanical properties of the weld. Small, globulitic grains are important for increased strength, ductility and toughness and for a low susceptibility to solidification cracking instead of large, columnar grains. This study shows the main influences on such weld metal grain refinement. Therefore, the influence of thermal conditions, the chemical composition of the weld metal and the number and type of solidification nuclei on the microstructure were classified for the TIG welding of three different aluminium alloys.
Surface modification of mild steel was undertaken using two covered electrodes and two tubular electrodes. The two covered electrodes are DIN 8555: E6-UM-60 and E10-UM-60GR; however, the two tubular electrodes are E10-GF-60GR1 and E10-GF-60GR2. Chemical analysis for the weld metal and XRD of the flux covering for covered electrodes and flux core for tubular electrodes were conducted. The most important factor in determining the wear resistance is the microstructure of the deposit layers. In similar carbon equivalent electrodes E10-UM-60GR and E10-GF-60GR1, electrode E10-GF-60GR1 (tubular) shows larger carbides area fraction and better wear resistance than electrode E10-UM-60GR (covered). This could be attributed to a lower dilution associated with tubular electrode compared with covered electrode. The two tubular electrodes showed higher wear resistance than the covered electrodes which is mainly due to the larger Fe-Cr carbide precipitation area fraction.