MIG welding

In gas metal-arc, also called metal inert gas (MIG) welding, the arc is stmck between the workpiece and a metal electrode that is consumed as it is transferred in the form of molten droplets across the arc into the weld joint. Using a predominantiy argon shield gas, the droplets are transferred with Httie radial dispersion. Using pure helium, on the other hand, the droplets are larger and have more of a tendency to spray radially from the arc s axis. 

Figure 10-158B. Platecoil double- and single-embossing designs for standard units. The Platecoil is fabricated using resistance, spot, seam, and Tungsten Inert Gas (TIG) and/or Metal Inert Gas (MIG) welding techniques in order to hold and seal the two plates together. (Used by permission Cat. 5-63, 1994. Tranter , Inc.)...

MIG-welding metal-inert gas arc welding using a consumable electrode. 

Metal inert gas (MIG) welding, 27 369 Metal-insulator-semiconductor (MIS) capacitor, 29 140-143 Metal-insulator-semiconductor devices, 22 191, 192... 

Figure 3 (submerged arc welded AISI 304 plate) and Figure 4 (P-Al Mg 4,4 UNI 5452 MIG welded plate), both belonging to new vessels, show the presence of porosity (gas bubbles) imputable to a discontinuous welding speed and to high values of process electrical parameters.

Figure 5. Low penetration defects in a MIG welded P-Al Mg 4,4 UNI 5452 plate of a new vessel.

Hardness. Post-friction stir weld hardness results for JIS6N01-T5 show the typical W -shaped curve, as previously seen for other age-hardenable aluminum alloys (Ref 54, 67, 68). For the as-welded condition, postweld hardness decreases from -105 to -75 HV, a decrease of 28%, with hardness in the nugget -5 HV higher than the HAZ. Compared to MIG welding, the minimum hardness in the friction stir welded nugget is higher (78 versus 62 HV), and the size of the HAZ is considerably less (Ref 67). This would be expected due to the lower and more localized heat input associated with FSW. This... 

Other hardness observations of interest include those of Bassett et al. on 7017, where FSW was compared to MIG welding, illustrating a larger HAZ in the friction stir weld zone (Ref 77) Li et al. (Ref 82), where direct correlations are made between hardness values and conductivity profiles for a variety of postweld heat treatments following FSW in 7249 and the work of Jata et al., where postweld heat treatments in a 7050-T7451 alloy illustrate the ability to restore the weld nugget to near-parent-metal hardness, but the hardness minima troughs are unaffected in the HAZ (Ref 76). 

Fig. 11. Comparison of tensile properties of MIG-welded plate as-welded, bead-off, at 75° and -320°F.

In the MIG welding process, an electric arc is established between the work piece and a wire electrode. The electrode is continuously fed by a wire feeder through a torch. The arc continuously melts to form the weld puddle. An appropriate gas or gas mixture shields the weld area from atmospheric contamination. The MIG process has advantages of high deposition rates, faster speed, and excellent weld quality. A drawback of MIG is that base metal dilution is more than other processes. As a result, a second layer of weld may have to be applied to achieve the desired hardness. 

Figure 51.1 The principles of a) MIG welding and b) TIG welding. (Reprinted from ref [51.3] with permission.)...

Metal inert gas (MIG) welding, with a hand held pistol bringing together an automatically fed consumable wire electrode with inert gas shielding... 

Porosity. Porosity is often regarded as an inherent feature of MIG welds. The main cause of porosity is absorption of hydrogen in the weld pool that forms discrete pores in the solidifying weld metal. The most common sources of hydrogen are hydrocarbons and moisture from contaminants on the parent material and filler wire surfaces, and water vapor from the shielding gas atmosphere. Even trace levels of hydrogen may exceed the threshold concentration required to nucleate bubbles in the weld pool, aluminum being one of the metals most susceptible to porosity. ... 

Several alloys are compatible for welding purposes. Rolled or extruded semi-products of the 3000, 5000 and 6000 series can be joined with castings in alloys 42100 (A-S7G03), 42200 (A-S7G06), 43000 (A-SIOG) and 71000 (A-Z5G) by means of TIG and MIG welding. 

Unlike with copper-containing alloys, TIG and MIG welding is possible with alloys of the 7000 series without copper, such as 7020. During cooling, the HAZ is air quenched, and will exhibit mechanical properties close to a T4 temper. This is an advantage compared to alloys of the 5000 series in which the HAZ is in the annealed temper [26]. 

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