The material flow and mechanical properties of similar and dissimilar friction stir welds joining 6061-T6 to 2014-T6 aluminium alloys are compared. According to various sets of welding parameters cold, medium and hot welds were achieved. Sets of welding parameters were selected so that similar welds are defect-free. They show an onion-ring microstructure of the nugget. They have joint efficiencies of 87% and 85% for cold and hot 2014-2014 welds, and 73% and 64% for cold and hot 6061-6061 welds respectively. The low efficiency of 6061-6061 hot welds is due to the fact that the chosen welding parameters represent very slow welding speeds for this alloy. Dissimilar welds are performed with the hardest material either on the advancing side or on the retreating side and with three welding conditions. Macrographic examinations reveal complex flow patterns in the weld nugget of dissimilar welds. Depending on the welding conditions and the position of the hardest alloy (Advancing Side or Retreating Side), three different patterns are observed. These are a clear onion ring, an 8-shaped nugget with a sharp separation between the nugget and the 6061 alloy or a rough mixing of both alloys. Large cavities opening to the surface may appear for welding speeds equal or higher than 150 mm/min. If the 2014 alloy is placed on the advancing side, a shift of the tool towards the 2014 alloy may reduce the risk of surface defects occurrence. Surface defects occurrence seems to be highly affected by the alloy remaining on the tool after welding. Both flow pattern and surface conditions have a large influence on the tensile and fracture properties of the weld.
Flow pattern and mechanical properties of dissimilar friction stir welds joining 6061-T6 to 2014-T6 aluminium alloys
2010
7 Seiten, 3 Bilder, 4 Tabellen, 16 Quellen
Conference paper
English
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