Improved microstructure and properties of 6061 aluminum alloy weldments using a double-sided arc welding process
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I. INTRODUCTION
AS one of the most commonly used heat-treatable aluminum alloys, 6061 is available in a wide range of structural shapes, as well as sheet and plate products. Typically, it is used in autobody sheet, structural members, architectural panels, piping, marine applications, screw machine stock, and many other applications.[1] Generally, this alloy is easily welded by conventional arc welding processes (gas metal arc welding and gas tungsten arc welding (GTAW)) and highenergy processes (laser-beam and electron-beam welding). However, certain characteristics, such as solidification cracking, porosity, heat-affected zone (HAZ) degradation, etc., must be considered during welding, due to the greater amount of alloying additions used in this alloy.[2–5] Because of high-energy density and low overall heat input, laser beam and electron beam welding processes possess the advantage of minimizing the fusing zone and HAZ[5] and producing much deeper penetration than arc welding processes.[6] However, their high cost limits their usage in industry. Currently, the authors have developed a new welding process called “double-sided arc welding” (DSAW).[7–9] In this process, as shown in Figure 1, two torches (such as plasma arc torch and gas tungsten arc (GTA) torch, or dual GTA torches) are placed on the opposite sides of a base metal plate to increase penetration. They are directly connected to two terminals of a single power supply. The welding current loop becomes negative terminal - anode torch - workpiece cathode torch - positive terminal instead of the conventional negative terminal - anode torch - cathode workpiece - positive terminal. As a result, current flow concentrates the arc and improves weld penetration, resulting in a reduction in heat input. For example, in order to penetrate 6.5-mm-thick Al plate, regular AC GTAW needs two passes, but AC double - sided GTAW requires only one pass.[8] In addition, the Y.M. ZHANG, Associate Professor of Electrical Engineering, C. PAN, Research Associate, and A.T. MALE, Professor and Director, are with the Center for Robotics and Manufacturing Systems, University of Kentucky, Lexington, KY 40506-0108. C. PAN is on leave from Wuhan University of Technology, P.R. China. Manuscript submitted October 21, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
heat input in each pass for regular AC GTAW is approximately twice the heat input needed by the later.[8] The heat input is reduced to 25 percent. This process may provide a method to weld aluminum alloys without filler metal addition and to generate positive effects on productivity, cost, and weld quality. Extensive experiments have been performed on different metals and alloys using the DSAW process. Some unique characteristics and advantages have been obtained. For example,[7] on 6.4-mm-thick aluminum plates, the DSAW achieves 5.2-mm depth with 6-mm width, while regular variable polarity plasma arc welding (VPPAW) penetrates 3 mm with 8-mm width. The depth-to-width ratio is nearly doubled. In the present work, the microst
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