UDC 669.715:621.791.052 EFFECT OF HEAT INPUT ON THE MICROSTRUCTURE, STRENGTH AND CORROSION BEHAVIOR OF SHEETS OF ALLOY AA6061 AFTER COLD METAL TRANSFER WELDING Nilay Çömez 1, 2 and Hülya Durmuº 1 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov , No. 7, pp. 25 – 31, July, 2019. The effect of the parameters of welding conducted by the method of cold metal transfer on the geometry of the welding pool, the ultimate tensile strength, and the corrosion rate of welded joints of sheets from aluminum al- loy AA6061 is studied. The influence of the current, voltage, and heat input rate during welding on the proper- ties of the welded joints is analyzed. The welding parameters providing maximum ultimate strength and high corrosion resistance of welded joints of alloy AA6061 are determined. Key words: cold metal transfer welding, alloy AA6061, tensile strength, corrosion rate, Tafel dia- grams. INTRODUCTION Heat-hardenable aluminum alloy 6061 of the Al – Mg – Si system (series 6XXX) is used widely in the form of sheets and plates in various structures [1, 2]. The hardening phase is Mg 2 Si [1, 3]. The combination of high strength and corrosion resistance makes the alloy suitable for aviation, electrotechnical and automotive industries, marine struc- tures, screw machine stock, architectural panels, piping, etc. [1, 2, 4]. From the standpoint of protection of environment, light materials become very important in engineering applications, especially in transportation. However, welding of thin alumi- num sheets involves several problems including burning through and distortion or deformation of the sheets [5, 6]. These problems are eliminated by laser beam welding, which is characterized by a high welding speed and a low heat input [7]. However, laser beam welding of aluminum sheets has some difficulties. The low fluidity of aluminum at high tem- peratures and the high reflectivity of aluminum give rise to deep cones in the liquid pool and result in porosity; magne- sium and zinc evaporate from the welding pool [7, 8]. The newly developed method of cold metal transfer (CMT) welding has turned out to be suitable for welding alu- minum, 3 due to the absence of spatter of the liquid metal and low values of the current intensity, voltage and heat input [9, 10]. The process is characterized by short circuit, pulsed voltage and welding current maintained by digital computer control [6, 10]. The welding wire performs cyclic reciprocal motion 63 times per second on the average (at most 70 times per second) at alternately repeated hot and cold cycles [11]. Aluminum alloys have high corrosion resistance in vari- ous media due to the presence of a 2 – 4-nm-thick protective oxide layer on the surface [12, 13]. However, the protective layer is deteriorated in saline water due to the action of Cl – ions; localized corrosion develops in alloy AA6061 around intermetallic particles [13 – 15]. Coarse intermetallic parti- cles form in alloy AA6061 during casting. They act as cath- ode points, and this causes dissolution of the aluminum ma- trix in the corrosive medium. The size and the distribution of the intermetallic particles may change during the welding thermal cycle [14, 15]. The aim of the present work was to study the mechanical properties and the corrosion behavior of thin sheets from al- Metal Science and Heat Treatment, Vol. 61, Nos. 7 – 8, November, 2019 (Russian Original Nos. 7 – 8, July – August, 2019) 421 0026-0673/19/0708-0421 © 2019 Springer Science+Business Media, LLC 1 Manisa Celal Bayar University, Engineering Faculty, Department of Metallurgical and Materials Engineering, Manisa, Turkey. 2 E-mail: nilay.comez@cbu.edu.tr. 3 CMT is a welding process with feeding of wire into the welding zone; the heat of the arc fuses only the end of the wire, the formed liquid drop detaches during the reverse motion of the wire and joins the liquid pool. The process is implemented only with com- puter control (P. Kah, R. Suoranta, and J. Martikainen, “Advanced gas metal arc welding process,” The International Journal of Ad- vanced Manufacturing Technology , Vol. 67(1 – 4), pp. 655 – 674). DOI 10.1007/s11041-019-00440-z