Metal Transfer in Aluminum Alloys

Metal Transfer in Aluminum Alloys With the 5000 series aluminum alloys or Mg-containing aluminum filler metals, high vapor pressure elements in the filler metal cause a breakdown in the stability of metal transfer which, in turn, results in a high level of spatter formation BY R. A. WOODS ABSTRACT. Metal transfer has been metal transfer process, and aluminum ness. To aid in the evaluation of the studied while welding aluminum by itself has been the subject of several. films, a motion picture analyzer was the GMAW process. Particular atten In the present work, we undertook a available which made possible a tion has been paid to the role of high systematic study of metal transfer in a frame-by-frame analysis of each film. vapor pressure alloying elements in variety of aluminum alloys. Examina Included in the investigation were determining the mode of metal trans tion of high speed cine (motion pic alloys taken from commercial and spe fer. ture) films enable the behavior of a cially produced lots of Vw in. (1.59 mm) It is shown that the transfer charac range of alloying elements and con diameter 1100, 2319, 3003, 4043, 6063, teristics of all alloyed filler metal wires centrations to be evaluated. Some 5050, 5183, 5254, 5556, and 5039 alloy depend upon the concentration of understanding of the mechanisms of filler metal wires. In addition, high high vapor pressure alloying elements weld metal transfer in aluminum alloys purity binary alloys were made up incorporated in the wire. The presence was developed, accounting for fea containing 5% zinc and 1.5% lithium. of a high vapor pressure element tures which, in the more important Compositions of the alloys used are causes breakdown in the stability of commercial filler metal wires, contrib shown in Table 1. metal transfer, which in turn results in ute to welding smut, spatter, and gen For the filming, automatic welding a high level of spatter formation. Such eral clean-up problems. In addition, was normally performed at 260 A on behavior is normally found when from some of the reactions observed, 1100 alloy base plates with a 75% welding with the 5000 series or magne it has been possible to estimate the helium-25% argon shielding gas mix sium-containing aluminum filler al temperature of molten droplets within ture. The exception was the lithium loys. the arc. alloy which was fabricated to %< in. Explosive phenomena occurring (1.19 mm) diameter wire. This was during metal transfer have indicated Experimental Procedures welded at 150 A giving the same cur that the average temperature of drop rent density. During all the filming, the lets during transfer is approximately The droplet transfer process was arc was considerably longer than that 1700°C (3092°F). This agrees well with filmed by high speed, color cine pho regarded as optimum for high quality calculations based upon heat input tography using a camera capable of aluminum welding, but the spray and electrode burnoff considerations. taking 11,000 frames per second (fps). transfer and long flight path facilitated Normally the filming was done at 5,000 observation of the individual droplets. or 11,000 fps although later in the Power was supplied by a motor gener Introduction study, when it became desirable to ator with a drooping volt/ampere The phenomena of metal transfer in film at even higher speeds, an adaptor characteristic, ensuring an almost rip arc welding and especially the gov was used which permitted filming at ple-free, constant current supply. erning mechanisms received consider 44,000 fps. Photography was enhanced able attention during the late 1950's by a Xenon backing light which Results and early 1960's. Perhaps the most reduced interference from arc bright- 1 definitive study was that by Salter Examination of the films showed where the contributions of the various that the modes of transfer exhibited by arc forces to metal transfer were Paper presented at a session sponsored by aluminum and its alloys could be clas assigned quantitative values. In work the Aluminum Alloys Committee of the sified into two distinct groups. The 2 of a more qualitative nature, Cooksey Welding Research Council at the AWS 60th first group, which showed relatively investigated transfer with many met Annual Meeting held in Detroit, Michigan, smooth droplet growth and detach als, different shielding gases, and with during April 2-6, 1979. ment, contained commercially pure both reverse and straight polarity. R. A. WOODS is Staff Research Metallur aluminum (1100 alloy) and the alloys Many other investigations have been gist, Kaiser Aluminum & Chemical Corpora of manganese (3003), copper (2319), concerned with various aspects of the tion, Pleasanton, California. and silicon (4043). Behavior of the WELDING RESEARCH SUPPLEME NT I 59-s Table 1—Welding Wire Quantometer Estimates, % Alloy Fe Cu Mn Ms Cr Zn Others 1100 0.13 0.37 0.14 0.01 0.02 0.009 0.03 0.008 3003 0.07 0.56 0.15 1.19 0.01 0.01 0.02 0.02 4043 5.04 0.19 0.02 0.01 0.03 0.02. 0.02 0.01 2319 0.12 0.29 6.4 0.25 0.02 0.005 0.12 0.12 6063 0.41 0.18 0.007 0.002 0.49 0.00 0.001 0.006 5050 0.005 0.005 0.00 0.002 1.39 0.00 0.00 0.001 5254 0.07 0.13 0.00 0.006 3.57 0.21 0.02 0.02 5183 0.08 0.26 0.01 0.62 4.73 0.06 0.007 0.02 5556 0.11 0.21 0.02 0.71 4.93 0.09 0.01 0.09 5039 0.05 0.24 0.02 0.46 3.97 0.13 2.64 0.02 AI-5% Zn 0.05 0.09 0.005 0.002 0.003 0.001 5.0 0.002 AI-1.5% Li 0.010 0.003 0.004 0.001 0.01 0.001 0.005 0.001 1.48 Li second group was much more unsta 5% Zn filler metal wire was much more formation is shown in Fig. 2. Growth ble with a ragged, explosive type of violent than with the 5% magnesium began smoothly with the same initial, transfer. This was associated with the wire. Pendant droplet instability set in pale lilac arc coloration as with the magnesium, zinc, and lithium-contain at an early stage of the droplet growth pure metal. However, magnesium va ing alloys. cycle, and the frequent droplet disin porization soon gave the arc a distinc In the smoothly transferring, pure tegration produced high levels of spat tive green tinge which became more aluminum group, each droplet grew in ter and welding smut. Slightly less intense as the droplet growth pro a relatively undisturbed fashion until explosive behavior was noted in 5039 gressed. the detaching forces in the arc alloy filler metal wires which con The first indication of instability exceeded the restraining surface ten tained 2.5% Zn and 3.5% Mg. occurred when the droplet was about sion force. During the initial stages of Since the most detailed studies were one-quarter formed. A small distur droplet growth the apex of the arc was of the widely used commercial 5183 bance or puckering effect appeared on at the base of the pendant drop and alloy, the behavior of this will be the surface. This was usually followed the arc core was pale lilac in color. As described as being typical of the by a brief return to stable, quiescent droplet growth proceeded, the core group. The general sequence of drop growth. However, this first disturbance coloration gradually disappeared was invariably followed by greater while the luminous area of the arc instability which rapidly increased in extended to envelop the whole drop severity until large eruptions occurred let. which ejected vapor and showers of Detachment occurred by a smooth small globules of liquid metal from the pinching-off of the drop from an elon drop. This explosive behavior contin gated neck—Fig. 1. Frequently, a por ued until the droplet detached. tion of the liquid metal forming the Detachment rarely occurred by the neck would ball up to form small transfer of a discrete drop; usually the secondary droplets which were usually drop was almost completely shattered thrown out of the central region of the and the metal separated from the elec arc. These drops collected to form a trode in a highly irregular and dis small quantity of spatter on the plate torted form, accompanied by much surface beside the weld bead. Smut spatter. Immediately after separation, levels were low in all these alloys. In the eruptions and general drop distur general, the behavior patterns of this bances ceased and surface tension group conformed closely to the classi forces tended to mold the detached cal droplet growth and detachment drop to a spherical shape. Thereafter, processes described by earlier au passage across the arc was quite thors. smooth except for the occasional Transfer in the second group of drops and even spatter balls which alloys was generally much more unsta would suddenly balloon out, increas ble, changing from smooth to explo ing in size many times, finally bursting sive during the cycle of each drop and shattering completely—Fig. 3. formation. The explosive tendency These explosions, which occurred over varied with each individual alloying a period of about 1 ms, ejected more element and its concentration. In the vapor and considerable quantities of magnesium alloys, as the magnesium spatter outside the arc.

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