The welding of aluminium and its alloys
Defects in arc welding
A list of weld defects and their causes is given in Table 11.1. Other defects not listed are mainly those of geometry and include misshapen and incorrectly sized welds, variable cap width and height, weld face roughness, incomplete weld fill and asymmetry of fillet welds. These are all welder-induced problems, requiring improved shop-floor discipline and/or welder retraining.
If the required acceptance level for the defects listed above is not contained within a relevant application standard then it is the responsibility of the designer to select the appropriate quality level. A readily available specification to which the designer may refer for guidance is BS EN 30042 ‘Arc Welded Joints in Weldable Alloys, Guidance on Quality Levels for Imperfections’. This document contains three quality levels, B stringent, C intermediate and D moderate, the choice of which depends upon design considerations, subsequent fabrication activities such as rolling or pressing,
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Causes |
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Defect Name |
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Description |
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ISO 6520 Defect no. |
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4011 (Fig. 11.1) |
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Lack of inter-run fusion Failure of weld metal to fuse to preceding run |
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4012 (Fig. 11.1) 4013 (Fig. 11.1) |
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Lack of root fusion |
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Poor restart (cold start) Lack of fusion beneath weld start position Lack of penetration Failure to achieve the minimum penetration specified by design Insufficient (lack of) root Failure of weld metal to penetrate |
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517 402 4021 (Fig. 11.2) 504 (Fig. 11.3) 501 (Fig. 11.4) 501 (butt) |
Lack of side wall fusion
penetration Excess penetration Root or face undercut Excess convexity
Failure of weld metal to fuse to weld preparation
Root bead fully penetrated but not fused to root face
fully root faces
Unacceptable protrusion of the root bead
Notch parallel to weld at weld toe. Prevalent at top edge of PB fillet
Excess weld metal on the face of a
Current too low, travel speed too high, incorrect torch angle, oxide film on prep. surfaces, inadequate joint cleaning, weld preparation too narrow
Current too low, travel speed too high, incorrect torch angle, inadequate inter-run cleaning
Current too low, voltage too low, travel speed too high, root face too thick, root gap too wide, incorrect torch angle, inadequate cleaning
Incorrect welder technique (see Section 7.4.1), poor earthing
Current too low, travel speed too high, incorrect torch angle, incorrect weld prep.
Current too low, travel speed too fast, root face too thick, root gap too small, incorrect torch angle, misalignment
Current too high, travel speed too slow, root gap too wide, root face too thin
Current too high, travel speed too fast, incorrect torch angle, inadequate cleaning
Current too high, travel speed too low,
503 (fillet) Excess weld metal
(Fig. 11.5) (excess cap height)
511 Incomplete fill (face
(Fig. 11.6) concavity or missed
edge). Insufficient throat in fillet welds
515 Root concavity
(Fig. 11.7)
510 Burn-through
506 Overlap (roll-over)
(Fig. 11.8)
201 Porosity
2016 Worm-hole (piping)
2024 Crater pipe
100 Solidification cracking butt or fillet weld
Insufficient weld metal fill giving groove on weld face resulting in insufficient throat
Root pass 'sucked back' to give a shallow groove
Localised loss of weld pool in root
Weld metal that has rolled over at the edges and not fused to the parent metal. May be face or root
Gas entrapped in weld metal giving a cavity. May be localised, uniformly distributed or aligned
Elongated gas cavity formed by solidification of large weld pool
Elongated cavity in the weld finish crater
Cracks in weld produced during welding
incorrect torch manipulation
Poor welder technique, travel speed too fast, current too low, incorrect torch positioning
Current too high, root gap too wide, root face too thin
Current too high, travel speed too slow, root face too thin, root gap too large
Weld bead too large, current too high, travel speed too slow, prevalent in horiz.- vert. welds, inadequate cleaning
Dirty consumables, poorly cleaned or dirty weld preparations, contaminated shield gas, contaminated (hydrogen containing) parent metal - especially castings, oxide film on parent metal, porous gas hoses, leaks in gas delivery system, condensation, poor joint design trapping gas (see Chapter 2)
Excessive current, travel speed too slow
Incorrect welder technique - lack of crater fill
Incorrect choice of filler metal, failure to control dilution, incorrect edge preparation, crack susceptible parent
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ISO 6520 Defect no. |
Defect Name |
Description |
Causes |
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metal, high restraint, high heat input (see Chapter 2) |
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104 |
Crater cracking |
Short longitudinal or star-shaped crack in finish crater |
Incorrect welder technique, lack of crater fill |
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100 |
Liquation cracking |
Cracking in the HAZ or in previously deposited weld metal |
Incorrect filler metal, crack sensitive parent metal, high restraint, high heat input (see Chapter 2) |
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303 |
Oxide entrapment |
Oxide films trapped within the weld metal |
Oxide films in or on parent metal, oxide films in or on filler metal, oxygen in shield gas, poor gas shielding, inadequate cathodic cleaning |
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3034 |
Puckering |
Excessive oxide entrapment from weld pool turbulence |
Poor gas cover, very high weld current |
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3041 (tungsten) 3042 (copper) |
Tungsten or copper inclusions |
Accidental contact of the electrode (TIG) or contact tip (MIG) |
Poor welder technique, incorrect mechanised set-up |
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602 |
Stray arc strike |
Accidental arcing outside weld prep. |
Welder carelessness |
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602 |
Spatter |
Droplets of weld metal expelled from weld pool |
Poor welder technique, incorrect weld parameters |
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606 |
Underflushing |
Thinning below design thickness |
Excessive grinding |
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Lack of Inter-run Fusion |
11.1 Defects 4011 lack of side wall fusion, 4012 lack of inter-run fusion, 4013 root fusion.
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11.2 Defect 4021. |
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11.3 Defect 504. |
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UC |
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(a) Butt EC |
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IF 11.6 Defect 511. |
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Root concavity (RC) 11.7 Defect 515. |
static or dynamic loading, temperature and corrosive conditions and the consequences of failure.
