Investigation on strength and corrosion behaviour of friction stir welded similar and dissimilar aluminium alloys

Sheet materials of the alloys 6056 and 2024A were joined using the friction stir welding technique. Similar and dissimilar butt welds were produced. Strength and corrosion behaviour of the joints were investigated in different heat treatment conditions. Hardness profiles across the weld revealed minima in the heat affected zones, being very pronounced at the advancing side of the joints. The hardness of the nugget zone increased after post-weld artificial aging. Strengths of post-weld heat treated similar 6056 and dissimilar 2024A/6056 joints approached 90 and 85%, respectively, of the ultimate tensile strength of 6056-T7X. As found by electrochemical measurements, alloy 2024A-T3 exhibited the most noble corrosion potential and artificially aged alloy 6056 the most active potential. Besides microstructural changes caused by the welding process, galvanic coupling affected the corrosion behaviour of friction stir welds, in particular with joints of dissimilar aluminium alloys, as indicated by accelerated corrosion of alloy 6056 in the nugget region. Intensified corrosion attack was also observed in the heat affected zones.