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. content increased, transfer changed The unstable and characteristically from smooth, almost pure metal type explosive type of droplet growth cycle transfer in the 6063 alloy (0.49% Mg) to described above was common to all a very violent, ragged mode in the high the magnesium-containing alloys and magnesium alloys (5556 alloy—5.0% became more intense as the magne­ Mg). sium content in the filler metal In general, the lithium alloy trans­ increased. In alloy 6063 (0.49% Mg), Fig. 1—Droplet transfer with 1100 alumi­ the mode of transfer was midway ferred much more smoothly than did num. The droplet forms smoothly, then between the two groups. Approxi­ the equivalent magnesium-containing detaches from an elongated liquid metal alloy, and the droplets tended to be neck which coalesces into small secondary mately half of the transfer events took larger upon separation. Transfer with a droplets place smoothly and regularly just as

60s FEBRUARY 1980 B

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Fig. 2-Droplet transfer in 5183 alloy. In frames A1-A4, droplet growth is very smooth. In A5 a small disturbance can be faintly seen at the drop tip and the first surface ripples appear shortly thereafter. After frame B5 the droplet becomes very roughened and disintegration begins, continuing until detachment occurs. After detachment in frame E4, a small explosion occurs within the droplet, deflecting the plasma stream to the right, and small spatter balls are formed as the thin metal sheet coalesces. Thereafter, the droplet rounds off and enters the pool. Filmed at 5,000 fps. Time between frames is 0.2 ms with the pure metal. Most of the was followed by breakdown and marily because few complete droplet remainder of the drops would show explosive disintegration of the rather transfers occurred. small explosions and instabilities just elongated, molten metal tip. The Transfer characteristics with the prior to transfer, while a very few explosive reactions were more intense 1.5% lithium alloy were considerably would shatter completely as described than with alloy 6063 but occurred less severe than in the aluminum- for alloy 5183. However, all of these more slowly than in the higher magne­ magnesium alloys. All droplets reactions occurred much more slowly sium alloys, allowing some of the pen­ showed some degree of the ragged and with less intensity than in alloy dant droplet explosions to be captured explosive type of transfer but the onset 5183. Once detached, the 6063 alloy on film —Fig. 5. Compared with alloy of this was delayed until late in each drops became very stable and from 6063, more in-flight droplet explosions growth cycle. The explosions were several hundred feet of film only one were observed; however, these were rarely sufficient to shatter the drops instance was observed of an explosion much rarer than in alloy 5183. and none was observed to balloon out occurring during transfer across the The most violent transfer we ob­ and explode during flight across the arc—Fig. 4. served was associated with the Al-5% arc. Vapor emission levels were very Transfer with alloy 5050 (1.39% Mg) Zn alloy. An example is shown in Fig. 6 high and a bright pink ionized vapor conformed more closely to the Al-Mg where complete disintegration of the cone was built up in the arc. pattern, but was still significantly less pendant droplet occurs. Most transfers Since the reactions were less violent explosive and violent than with alloy in this alloy were of this nature. No than in the magnesium alloys, a frame- 5183. Preliminary smooth drop growth in-flight explosions were observed pri­ by-frame examination of these films

WELDING RESEARCH SUPPLEMENT I 61-s was made. This showed that the rag­ tortion. Often when the cavity refilled, were sometimes powerful enough to ged transfer was associated with small a single small spatter ball would be fragment almost the whole of the pen­ vapor bursts or explosions occurring ejected from its center. The collapse of dant droplet, and frequently, simulta­ on the underside of the pendant this first cavity was soon followed by neous multiple explosions were ob­ drop. the formaton of others, causing pro­ served. Figure 7 shows the formation of one gressively greater distortion of the of these internal vapor bursts and the droplet. Interpretation of the Results ring of metal vapor which was ejected The explosive stage was rapidly outside the shielding gas stream. These reached when small vapor bubble The most distinctive differences be­ bubbles were nucleated beneath the eruptions could be seen bursting from tween those alloys which conformed liquid metal surface. Their growth and the underside of the drop. These bub­ to the Al-Mg pattern and those which rupture was extremely rapid, often bles were nucleated beneath the liq­ occurring in approximately the time uid surface and when they burst, vapor lapse of one frame (2 X 10~4 s). A streams were visible momentarily as frame-by-frame examination of trans­ narrow, elongated cones giving the fer with 5183 alloy filmed at 11,000 fps appearance of small shadows extend­ revealed similar phenomena, but the ing most of the way down the arc. reactions were much more violent and Owing to their very short lifetime and too rapid to allow separation of the rapid formation, these induced a flick­ sequence of events during the onset of ering effect in the arc. instability. Accordingly, additional Towards the final stages of droplet films were shot at 44,000 fps while growth, the massive internally nu­ welding with this filler metal alloy. A cleated explosions were observed frame-by-frame analysis of these films which usually ejected large quantities allowed the droplet reactions and of spatter and emitted a burst of vapor, TTf accompanying arc disturbances to be distorting the arc column and often observed in more detail. sending a vapor stream outside the Instability in the pendant droplet central arc region. These explosions began with the formation of a small crater or depression on the droplet surface. This filled extremely rapidly (< 0.2 ms) and ripples running out from this crater, and a slight recoil, agi caused the first detectable droplet dis­ I T r Tyr

Fig. 4—An inflight ex­ plosion of transfer­ ring Al-O.49% Mg al­ loy (6063). This alloy showed very rare in­ flight explosions Trf

X Fig. 5—Transfer sequences in aluminum alloy 5050: A—This sequence shows the formation of an internal vapor burst which distorts the pendant droplet. B—Two pen­ dant drop vapor bursts are shown. The first, beginning fust before the end of exposure of the second frame, ruptures during expo­ sure of the third frame. Also in this frame, a second burst has occurred and is captured at its maximum size and in the first stages of bursting. The distortions caused by these two events in the pendant droplet are shown in the fourth frame and the droplet which detaches is extremely ragged. C—A Fig. 3—In-flight explosions of 5183 alumi­ massive vapor explosion occurs which com­ num alloy droplets pletely disintegrates the pendant droplet

62-sl FEBRUARY 1980 B

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Fig. 6—Transier in AI-5% Zn alloy showing the early onset of pendant droplet instability and complete disintegration of a detaching droplet sities would be of the order of 13,000 A/cm2, so lower temperatures and less evaporation than for the more massive behaved in the same manner as the particularly upon surface tempera­ solid anodes are likely. Vapor stream pure metal are the temperature/vapor tures. Unfortunately, there have been velocities are also likely to be lower, pressure relationships. Effects of metal few attempts at this type of measure­ but still apparently of sufficient force vapors in the arc upon metal transfer ment. Some data given in the Japanese to deflect the pendant droplet.2 2 4 have been observed before. Cooksey literature for low current (75 A), glob­ There have been several detailed found that the high vapor pressure ular type aluminum transfer indicate analyses of the heat balance in GTAW metals magnesium, zinc and cadmium, an average droplet temperature of arcs, but there is no comparable infor­ exhibited transfer characteristics 1550°C (2822°F). Calorimetric determi­ mation available for the more complex which were controlled by metal vapor­ nations for steel using higher welding GMAW system. However, by using ization. In their pure forms, these met­ currents yielded drop temperatures of s data presented in these GTAW studies als emitted vapor streams which were 2800-2900°C (5072-5252°F) which are and in particular that by Quigley et a/.! sufficiently intense to lift the pendant approximately at the boiling point of it is possible to make a crude estimate droplet away from the plate surface, iron (2860°C) (5180°F).' It seems prob­ of the heat input into the GMAW often projecting the detached drop able, therefore, that in higher current electrode tip. Following Quigley's out beyond the arc region. aluminum welding, temperatures analysis, the majority of the heat pro­ Considering the metals used in the would be higher than those measured duced at the anode is due to: present study, pure aluminum has a while welding at 75 A. 1. Electron potential energy. boiling point of 2520°C, (4568°F), Surface temperatures are even more 2. The anode fall. while zinc, magnesium and lithium difficult to obtain than bulk tempera­ 3. Electron thermal energy (Thomp­ boilat911oC(1672°F),1090oC(1994°F), tures, being largely controlled by the son effect). and 1342°C (2448°F), respectively.3 area of the anode spot. In work inves­ 4. Thermal conduction from the Manganese boils at 2060°C (3740°F), tigating electrical discharges, Cobine 6 arc. while copper boils at 2560°C (4640°F) and Burger found a temperature of and silicon at 3270°C (5918°F). Thus, in 3000°C (5432°F) for the molten spot Additional, less important sources of the aluminum alloys that were studied zone in large solid aluminum anodes. heating are: in the present work, a correlation is Under these conditions, evaporation 1. Radiation from the arc. readily apparent between the pres­ rates for aluminum were estimated to ence of a high vapor pressure alloying be in the range 7-90 gm/cm2/s with 2. Resistive heating. element in the filler metal and an vapor stream velocities quoted from Cooling of the drop occurs by: unstable form of metal transfer. 1 x 10' to 1 x 10'' cm/s.7 In the con­ 1. Radiation. ventional GMA welding arc, the anode The extent of metal vaporization in 2. Convection. spot probably covers the whole under­ the welding arc depends upon the 3. Evaporation. side of the pendant drop. Current den­ temperature of the droplet and more 4. Conduction.

WELDING RESEARCH SUPPLEMENT I 63-s Estimates of most of these quanti­ The above estimate indicates that work by Belton and Rao12 would give ties at the electrode tip (anode) of the approximately 26% of the heat devel­ boiling points some 300-400°C GMAW system are difficult to make. oped in the arc appears at the wire tip (540-720°F) higher than those shown However, we may assume that the and is used to melt and heat the in Table 2. Data shown for the alumi­ electronic heating components pre­ transferring droplets. num-zinc system were based on work 3 dominate and that the heat inputs to a Burn-off data for 5183 alloy" show by Bolsaitis.' The necessary thermody­ pendant drop due to thermal radiation that the melting rate under the condi­ namic data for the molten aluminum- and conduction from the arc are bal­ tions used in the present work is 0.756 lithium system have not been found; anced by the heat losses due to radia­ g/s. The heat needed to fuse this as a result vapor pressures for this alloy tion and metal evaporation from the quantity of alloy is 780 watts. The system were calculated assuming an drop, together with the losses due to remaining heat may be used to raise activity coefficient of unity. The ele­ forced convective cooling of the drop the temperature of the transferring liq­ ments copper, silicon, and manganese by cold gases drawn into the arc. On uid metal—Fig. 8. Assuming a constant are assumed not to affect the vapor this basis then some very approximate specific heat of 1.08 J g1 "K"1 for the pressure of aluminum significantly anode heat inputs can be calculated. liquid metal, the estimated average because of their high boiling points. As an example, the electron poten­ temperature of the droplets would be Examination of the data shows that tial energy at an arc current of 260 A, 1860°C (3380°F). Alloys with lower the aluminum alloys with a boiling assuming a work function of 4eV for burn-off rates such as 1100 or 4043 point lower than 2500°C (4532°F) aluminum, contributes some 1040 aluminum9 might be expected to be at exhibited a ragged mode of transfer. In watts. If the anode fall is assumed to a somewhat higher temperature. addition, those with a boiling point be 2 V, then the additional heat devel­ It is interesting to relate calculated below 1600°C (2912°F) showed fre­ oped by this means would be 520 droplet" temperature to the observa­ quent inflight droplet explosions while watts. The electron thermal energy, tions of in-flight exploding droplets those with boiling points between assuming an arc temperature near the which are summarized in Table 2. Also 1600°C (2912°F) and 2000°C (3632°F) drop of 8,000°K and an anode temper­ shown in Table 2 are boiling point data showed only rare explosions. These ature of 2,000°K, can be calculated to calculated for the various alloy sys­ explosions are believed to arise from contribute about 200 watts.* Electrical tems. Thermodynamic data for the alu­ the nucleation of internal vapor bub­ resistance heating of the drop is negli­ minum-magnesium system have been bles. The conditions under which gible (resistivity of aluminum at summarized by Hultgren,1" while more these bubbles nucleate are not well 3 understood, but it is assumed that they 1000°C = 0.3/xO/m). Therefore, the recent vapor pressure data have been are heterogeneously nucleated on effective energy input into the con­ given by Bhatt and Jarg." The results of small oxide inclusions, etc. Homoge­ sumable electrode while welding at the latter investigators are probably neous nucleation would require con­ 260 A is estimated to be some 1760 the most reliable and have been used siderably greater superheat, and the watts. to calculate the boiling points of the explosions would probably be more various aluminum-magnesium alloys catastrophic. used in this work—Fig. 9. *0°K = -273.1 "C. Calculations based on the earlier For an internal vapor bubble to form, the partial pressure of the alloy­ ing elements in these droplets must be greater than one atmosphere. Ransley 2200 and Talbot14 have stated that molten aluminum will not form hydrogen bubbles unless the partial pressure of 2000 the gas is greater by a factor of 1 • 2 than the 1 atmosphere solubility. Simi­ lar conditions may apply to internal nucleation of metal vapor bubbles. 1800 Since in any particular alloy system all droplets do not explode, either the superheat is not great or there is a paucity of suitable vapor bubble 1600 nucleation sites. In either case, the superheat is not likely to be above 300°C (572°F) as this

64-sl FEBRUARY 1980 over the area of the root of the arc where electron heating would be con­ Table 2-Thermal Data and Metal Transfer Properties for Aluminum Alloys centrated. During the drop formation In-flight cycle, the temperatures here increase /, Calculated Alloy boiling point, °C Transfer type explosions faster than the average drop tempera­ ture. 1100 2520 Smooth No We observed increasing levels of 4043 >2520 Smooth No metal evaporation in the arc until pre­ 2319 >2520 Smooth No sumably the surface reaches the boil­ 3003 -2520 Smooth No AI-1.5% Li —2300 Transition No ing point of the alloy. At this time the 6063 1950 Transition Very rare streams of surface vapor cause the first 5050 1780 Ragged Rare droplet distortion. As electron heating 5254 1600 Ragged Yes continues, local temperatures increase 5183 1560 Ragged Yes rapidly, soon becoming high enough 5556 1540 Ragged Yes on the underside to nucleate vapor 5039 <1500 Ragged Yes bubbles just beneath the surface, pro­ AI-5% Zn 1260 Ragged Yes ducing the small cone-shaped vapor bursts we have observed. Eventually, "°F = (°C) + 32 5 the temperature rise is sufficient to cause nucleation of more massive vapor bubbles, well within the body of droplet detachment and then con­ It appears that there is a basic differ­ the droplet. tracts to form small spatter balls which ence between the behavior of pure Depending upon the concentration are often thrown clear of the arc. This metals and the high vapor pressure and boiling point of the alloying ele­ is the predominant cause of spatter aluminum alloys. The explanation for ments, these vapor bubbles enlarge while welding with the 1100, 2319, this is not clear from the present work, rapidly and burst, causing varying 4043 type filler metal alloys, but con­ but it is suggested that high evapora­ degrees of droplet disintegration. tributes a relatively insignificant tion rates cause the surface regions qf amount with the aluminum-magne­ Once the liquid surface becomes alloy droplets to become deficient in sium and other high vapor pressure the high vapor pressure component. roughened by these disturbances; alloys. Therefore, the internal vapor pressures there may be a tendency for the elec­ become higher than those at the sur­ tron stream to concentrate through The phenomenon of exploding face, resulting in the nucleation of projecting areas, leading to a smaller drops in the steel welding arc has been reported earlier by Quigley1' and internal vapor bubbles. anode spot with enhanced localized 16 heating. This could lead to the explo­ Lucas. These authors show some cor­ The data indicating an average tem­ sive vaporization of the small projec­ relation of the explosive tendency perature of 1700°C (3092°F) for the tions and rapid changes in the area of with high inclusion and gas contents, droplets after detachment were ob­ electron impingement. These effects proposing that oxides are reduced to tained by indirect means and depend produce gaseous carbon monoxide may explain the catastrophic behavior upon the reliability of the vapor pres­ which is released internally. The over­ we observe in the aluminum/magne­ sure data assumed in the calculcations. riding cause of the explosions in alu­ sium alloys during the latter stages of Although there was good agreement minum is believed to be the volatile droplet growth where the shape dis­ between this temperature and that nature of the alloying elements incor­ tortion seems to promote further estimated from heat input considera­ porated in the filler metal. However, a tions, the latter value again depends breakdown in droplet stability. high vapor pressure alone is not suffi­ greatly upon the assumptions made. A cient to cause droplet instability and more direct method of temperature explosion since this effect was not measurement would obviously be Discussion reported in highly volatile pure met­ much more desirable. als.2 Although a considerable volume of The only value available at present is literature exists on metal transfer, ear­ lier workers have not reported the very violent reactions, associated with va­ porization, which occur while welding 2500 with aluminum-magnesium filler al­ loys. These reactions produce the 2300 copious quantities of spatter and smut deposited with these fillers in the GMAW process. The smut is formed 2100 - \ -6063 from condensed and oxidized vapors while the spatter comes from several Z 1900 5050 sources but predominantly from the E explosive disintegration of pendant | 1700 - 5183 droplets.

An additional cause of spatter is the 1500 - 5254 i in-flight explosion of droplets, al­ 5556 though under normal aluminum weld­ ing conditions, where arc lengths 1300 * would be short, droplets would fre­ quently reach the weld pool before I they could explode. Further spatter is 2 3 4 formed by the rupture of the neck Magnesium Content (wt.%) joining the droplet to the electrode. Fig. 9—Boiling point of alloys at the low magnesium end of the aluminum- This becomes elongated just prior to magnesium system

WELDING RESEARCH SUPPLEMENT I 65-s that quoted for low current, globular aluminum alloys results from the rup­ Welding, No. 2, p. 16, 1967. type transfer where droplet tempera­ ture and coalescence of the liquid 6. Cobine, J. D., and Burger, E. E., "Anal­ tures of 1550°C (2822°F) were ob­ metal forming the neck between the ysis of Electrode Phenomena in the High Current Arc," Jnl. of App. Phys., 26, No. 7, p. tained by calorimetric means. The dif­ pendant drop and the electrode tip. 895,1955. ference in droplet size between the 5. The average temperature of alu­ 7. Kimblin, C W., "Anode Voltage Drop globular and spray types of transfer minum alloy drops crossing a 260 A arc and Anode Spot Formation in D.C. Vacuum may make a significant difference to is estimated to be 1700°C (3092°F). Arcs," Jnl. App. Phys., 40, 4, 1969, p. 1744. the temperature of the droplets. 8. Quigley, M. B. C, et al., "Heat Flow to the Workpiece from a TIG Welding Arc," Acknowledgments Jnl. Phys. D: Appl. Phys., 6, 1973, p. 2250. Conclusions The author acknowledges the help 9 Unpublished work, F. E. Gibbs, Kaiser Aluminum & Chemical Corporation. 1. The modes by which metal trans­ of R. C. Miller and L. C. Fore in per­ 10. Hultgren, R., et al., "Selected Values fer occurs during GMA welding of forming this work. Thanks are also due aluminum alloys can be characterized of Thermodynamic Properties of Binary to Kaiser Aluminum and Chemical Alloys," Amer. Soc. Met., 1973. as: Corporation for permission to publish 11. Bhatt, Y. J., and |arg, S. P., "Thermody­ (a) A smooth type of transfer the work and to Red Lake Laboratories, namic Study of Liquid Aluminum-Magne­ with discrete, well-formed Santa Clara, California, for assistance sium Alloys by Vapor Pressure Measure­ droplets with the ultrahigh speed cine photog­ ments,' Met. Trans. B., 7B, June 1976, (b) An explosive transfer with raphy equipment. p. 271. ragged detachment, forming 12. Belton, G. R„ and Rao, Y. K„ "A drops which often explode Galvanic Cell Study of Activities in Magne­ while traversing the arc. sium-Aluminum Liquid Alloys," Trans. Met. References Soc. of A.I.M.F., 245, Oct. 1969, p. 2189. 2. Aluminum alloys which do not 1. Amson, j. C, and Salter, G. R., "An 13. Bolsaitis, P., and Sullivan, P. M., "The contain high vapor pressure alloying Analysis of the Gas-Shielded Consumable- Activity of Zinc in Liquid Zinc-Aluminum elements transfer smoothly. Metal Arc Welding System," Proceedings of Alloys from Isopiestic Measurements." 3. The degree of explosiveness Conference on Physics of the Welding Arc, Trans. Met. Soc. of A.I.ME., 245, July 1969, found in an aluminum alloy contain­ London, p. 133, 1962. p. 1435. ing volatile components increases as a 2. Cooksey, C.)., and Milner, D. R., "Met­ 14. Ransley, C. E., and Talbot, D. E. )., function of the partial pressure of the al Transfer in Gas Shielded Arc Welding," Zeits. fur Metali, 1955, 46, p. 328. alloying elements. Ibid. p. 123, 1962. 15. Quigley, M. B. C, and Webster, J. M., 4. High levels of spatter associated 3. Smithels, Metals Reference Book, 5th "Observation of Exploding Droplets in with the commercial aluminum-mag­ ed., Butterworths. Pulsed-Arc G.M.A. Welding," Welding 4. Ozawa, M., and Morita, T., "The Mea­ Journal, 50 (11), Nov. 1971, Research SuppL, nesium filler wires are caused by disin­ surement of Heat Quantity of Melted Met­ pp. 461-s to 466-s. tegration of the pendant and detach­ als," Jnl. Jap. Weld. Soc, No. 2, 1963. 16. Lucas, W., and Amin, M., "Effect of ing drops. Exploding in-flight drops 5. Pokhodnya, I. K., and Suptel, A. M., Wire Composition in Spray Transfer Mild contribute a smaller amount. "The Heat Content of Droplets of Electrode Steel MIG Welding," Metal Construction, Spatter in the smoothly transferring Metal in Gas Shielded Arc Welding," Auto. February 1975, p. 77.

WRC Bulletin 251 August 1979

Comparison of Three-Dimensional Finite Element and Photo- elastic Results for Lateral Connection, WC-12B2

This report was prepared by the Task Group on Laterals of the Subcommittee on Reinforced Openings and External Loadings of the Pressure Vessel Research Committee of the Welding Research Council. Presented in this report are the results of three-dimensional finite element analyses of a 45 degree photoelastic lateral pipe/vessel connection, subjected to internal pressure loading. Details of finite element modeling and analyses are described. Comparison of finite element peak stresses with photoelastic results, available in the literature, shows that the maximum deviation is twenty percent, with the photoelastic results being larger than the finite element results. The price of WRC Bulletin 251 is $10.00 per copy. Orders should be sent with payment to the Welding Research Council, 345 East 47th St., Room 801, New York, NY 10017.

66-sl FEBRUARY 1980