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Effects of process parameters on the evolving properties of dissimilar aluminium-copper friction stir welds
Akinlabi E. T1 and Akinlabi S. A2
1 Lecturer, 2 Doctorate candidate, Mechanical Engineering Department, University of Johannesburg, Johannesburg, South Africa.
Abstract
This paper reports the effect of processing parameters on the evolving properties of friction stir joints between 5754 Aluminium Alloy and C11000 Copper. Welds were produced by varying the rotational speed between 600 and 1200 rpm and the traverse speed varied between 50 and 300 mm/min. The welds were characterised through microstructure, microhardness, tensile testing and electrical resistivity. The weld cross sections revealed that good mixing of both materials joined was better achieved at low traverse speed of 50 mm/min. It was observed that the Ultimate Tensile Strength of the welds decreases as the welding speed increases due to better material flow and transport of materials during the welding process at low travel speeds. Tensile results of the welds revealed that about 60% of the welds produced had joint efficiencies greater than 70%. Higher Vickers microhardness values were measured in the Thermomechanically Affected Zones (TMAZ) and the Stir Zones (SZ) due to plastic deformation that has occurred during the welding process and also due to the presence of intermetallic compounds at the interface. These higher Vickers microhardness values were observed mostly in welds produced at 50 and 150 mm/min, welds produced at 300 mm/min have a fairly flat profile due to low heat input into these welds. At constant rotational speeds, it was observed that the joint electrical resistivities of the welds increases as the traverse speed decreases due to the heat input to the welds.
(a) Produced at 950 rpm and 50 mm/min
(b) Produced at 950 rpm and 150 mm/min
(c) Produced at 950 rpm and 300 mm/min