1.WELDING POROSITY DEFECTS
Detail Description：
Cavities formed when bubbles in the molten pool fail to escape during solidification. Aluminium alloy weld metal within the pores are mainly hydrogen pores. According to the formation location is divided into internal pores, near-surface pores and surface pores.
Causes：
✔ The thermal conductivity of aluminium is large, the molten pool cools quickly, which is not conducive to the escape of bubbles, and the solubility of hydrogen in the solidification point of aluminium alloys is reduced by about 20 times, which is the main reason for the generation of porosity.
✔ The air humidity at the welding site is large.
✔ Welding consumables, base material bevel and edge adsorption of moisture, oil, oxide film adsorption of water
✔ The flow rate of protective gas is too low or too high, the purity is not enough or there is moisture, the protective gas is too low or too high.
✔ Poor gas tightness of pipework.
✔ The angle of the welding torch is not reasonable.
✔ Incomplete root cleaning in double-sided welding, incomplete interlayer cleaning in multi-layer multi-pass welding.
✔ unstable or too long arc.
✔ Repeatedly starting the arc in the same part, too many joints.
✔ The length of the welding wire is too long, and the distance between the nozzle and the weldment is too large.
✔ Inadequate clearance at the root of the bevel.
✔ High sensitivity to porosity of the designed aluminium material.
✔ Poor accessibility to the welding operation.
✔ Spatter or damage to the torch nozzle.
✔ Excessive wind speed or magnetic bias blowing present in the welding area.
Protective Measure:
✔ Under the premise that the heat input meets the requirements, increase the welding line energy by reducing the welding speed, preheat the thick plate, etc. to increase the time of the molten pool, so that the hydrogen gas can escape.
✔ Control of air humidity in the welding site
✔ Clean the bevel and its edges of moisture, oil and gaseous film before welding.
✔ Protect the welding consumables and use high quality welding consumables.
✔ Control the flow of shielding gas and avoid cable flow.
✔ Correct angle of the welding torch.
✔ Thoroughly clean both sides of the weld and between layers of multiple passes.
✔ Keep the arc stable and not too long.
2. WELDING NON-INTEGRATION DEFECTS
Detail Description：
Refers to the weld metal and base metal or weld metal between the part of the weld metal is not completely melted and combined. It is classified according to the location of formation into: root unfused, sidewall unfused and interlayer unfused.
Causes：
✔ Insufficient heat input due to too little welding current or too fast a speed.
✔ The torch angle is unreasonable or the torch is not sufficiently swung.
✔ Interlayer temperature is too low.
✔ The workpiece is too thick.
✔ Unreasonable bevel shape and dead space.
✔ There are gas film and oil in the workpiece bevel and its vicinity, and between the layers.
✔ Inflow of slag during welding prevents intermetallic fusion.
Protective Measure:
✔ Selection of suitable welding parameters and torch angle (directional stable wire)
✔ interlayer temperature is reasonable.
✔ Preheat the thick plate.
✔ Reasonable design of bevel size, avoiding dead space.
✔ The bevel and the vicinity, the dirt and oxide film between the layer paths are cleaned thoroughly, and grooves are avoided. (Welding wire surface is good)
3. Welding crack defects
Detail Description：
Under the joint action of welding stress and other factors, the bonding force of metal atoms in the local area of the welded joint is damaged to form a new interface and the resulting gap. Cold cracks and hot cracks
Causes：
✔ Caused by segregation of alloying elements at the product boundary or by the presence of low melting point substances.
✔ The high coefficient of linear expansion, high shrinkage stress and wide melting temperature range of aluminium alloys result in welds that are susceptible to the formation of hot cracks.
✔ Excessive welding speed increases the strain rate of the welded joint, thus increasing the tendency to hot cracking.
✔ When pre-welding and interlayer cleaning is not thorough, inclusions in the weld can become a source of cracks.
✔ Oxide layers are often accompanied by high humidity, which can induce gas cracking.
✔ The depth-to-width ratio of the weld is too large, and too narrow a weld is prone to cracking.
✔ Welding filler metal and base metal mismatch, welding heat input is too large, weld design caused by welding stress is too large, the workpiece is subjected to a large degree of constraint, bevel clearance is not appropriate, position welding when the length of the weld channel and the thickness of the weld seam is too small, thick plate (greater than or equal to 8 mm) is not in accordance with the provisions of the preheating and so on are prone to cracking.
Protective Measure：
✔ Under the premise of reasonable heat input, reduce the welding speed appropriately.
✔ Use linear weld and small current multi-layer multi-pass welding as much as possible, and strengthen the heat dissipation speed to reduce the overheating of the molten pool.
✔ Adopt the welding method of heat concentration to prevent the formation of coarse columnar crystals with strong direction and improve the crack resistance.
✔ Pre-welding cleaning and interlayer cleaning should be in place.
✔ Appropriately increase the shape factor of the weld and avoid narrow and deep welds.
✔ Adopt welding filler materials that adapt to the characteristics of the base material.
✔ Choose reasonable welding sequence, try to allow the workpiece part of the free contraction.
✔ For high-strength aluminium alloy welded joints, the method of hammering with welding can change the stress distribution of welded joints.
✔ Select proper bevel clearance.
✔ Reasonable location welding length and thickness; preheat (slow heating and slow cooling to reduce welding stress) when the base material is thicker
4. WELDING IMPERFECTIONS
Detail Description：
Refers to the phenomenon of welding where the root of the joint is not completely fused.
Causes：
✔ Too little heat input due to too little welding current, too fast welding speed, etc.
✔ The arc is too long.
✔ Incorrect torch angle
✔ Bevel angle too small, blunt edge too large.
✔ V-weld root clearance too small.
✔ Dirt on the bevel.
✔ Magnetic bias blowing of the arc.
✔ Incomplete root cleaning and too low arc current in the back of a double-sided weld.
Protective Measure：
✔ Select proper welding current, welding speed, arc length and torch angle.
✔ Design reasonable bevels and blunt edges.
✔ Strictly control the assembly quality.
✔ Clean oxide film and oil before welding.
✔ Clean roots thoroughly when double-sided welding.
5. WELDING BURN-THROUGH DEFECTS
Detail Description：
It refers to the welding process, the melting depth exceeds the thickness of the workpiece, and the molten metal flows out from the back of the weld, forming a perforation defect.
Causes：
✔ Excessive heat input due to excessive welding current, too slow speed, etc.
✔ Too much assembly clearance before welding.
✔ Unreasonable bevelling of the weld.
✔ The workpiece is too thin.
✔ Too much distance between weld joints during spot welding, large deformation during welding, etc.
✔ can lead to burn-through.
Protective Measure：
✔ Select appropriate parameters such as welding current and speed when welding.
✔ Control the assembly clearance before welding.
✔ Add pads to the back of the weld if necessary.
✔ Adjust torch angle for thin plate welding.
✔ Spot-fixed welds are properly spaced to avoid distortion, wrong edges, etc.
6. Welding Edge Bite Defects
Detail Description：
Refers to along the weld toe, in the parent material part of the formation of the depression or groove, is due to the arc will weld the edge of the parent material melting does not get the molten metal sufficiently supplemented by the biting edge most of the continuous biting edge left gap. Too much biting edge is localised overrun, continuous biting edge is rare.
Causes：
✔ Arc heat is too high (e.g., too much current, too slow, etc.)
✔ The arc is too long.
✔ Unreasonable angle of the welding torch, unreasonable swing:back welding sequence is unreasonable, etc. can cause edge biting.
✔ Magnetic bias blowing of the arc during DC welding can also cause edge biting.
Protective Measure
✔ Select proper welding heat input, arc length, correct torch angle and swing.
✔ Reasonable welding sequence.
✔ Reduce or avoid magnetic bias blowing.
✔ Measures such as using flat welding as much as possible can prevent biting edge
7. Welding weld lump defects
Detail Description：
The phenomenon of liquid metal collapsing to the back of the weld due to too much heat input and too much molten metal during single-sided welding, with the back of the weld bulging and the front collapsing after forming.
Causes：
But rounded bumps are acceptable when they are not very large.
Protective Measure：
✔ Design reasonable weld form, bevel angle and blunt edge size
✔ Select proper welding parameters.
✔ Point the welding torch correctly.
✔ Control reasonable assembly clearance before welding.
✔ Develop a suitable process plan when the workpiece is thin.
8. Welding wrong side defect problem
Detail Description：
means that the two workpieces are staggered in a certain position in the thickness direction.
Causes：
✔ Raw materials are oversized.
✔ Assembly does not meet requirements.
✔ Misalignment during spot-fixing, priming and filler welding.
✔ Structures with a high number of intersecting welds are prone to misalignment.
Protective Measure：
✔ Strengthen the acceptance quality of raw materials.
✔ Strictly control the quality of assembly before welding.
✔ Discover and adjust the wrong edge in time during the process of spot solid welding, bottoming welding and filler welding.
✔ Avoid too many weld intersections as much as possible when designing the structur
9. Problems with welding couch defects
Detail Description：
Refers to the fact that at high temperatures the strength and plasticity of aluminium is so low that it cannot support the liquid metal in the molten pool, causing collapse.
Causes：
✔ Excessive weld heat input
✔ High weld filler due to large bevel angles and large fillet weld assembly gaps.
✔ Improper torch angle.
✔ Thin plate thickness.
Protective Measure：
✔ Control welding heat input, assembly clearance before welding.
✔ Bevel angle and torch angle are reasonable.
✔ Design the weld as close to the reinforcement as possible.
10. Problems of welding deformation defects
Detail Description：
Deformation caused by the high temperature of the arc, including shortening, angle change, bending deformation, etc.
Causes：
✔ The large coefficient of linear expansion, high thermal conductivity and low yield strength of aluminium alloys are the root causes of welding deformation.
✔ Excessive welding heat input, irrational welding sequence, large welding filler due to large assembly gap before welding, irrational positioning weld spacing, too many welds or irrational arrangement, irrational bevel dimensions and weld dimensions, etc. can lead to welding deformation.
Protective Measure：
✔ Select reasonable process parameters and welding sequence.
✔ Reasonable assembly clearance and positioning weld spacing before welding.
✔ Minimise the number of welding seams.
✔ Arrange the welding seams reasonably and try to make the welding seams symmetrically arranged.
✔ Choose interrupted welding as much as possible to avoid too much concentration of weld seams.
✔ Pre-add counter-deformation if necessary.
✔ Choose reasonable restraint methods or jigs to control the deformation according to the specific conditions of the members, especially when welding thin plates.
11. Problems of blackening defects in welded seams
Detail Description：
Refers to both sides or ends of the weld will have a black phenomenon, this black is some of the black smoke like material especially black, especially after welding aluminium-magnesium wire, black smoke phenomenon is more obvious
Causes：
✔ Insufficient purity of shielding gas.
✔ High impurities in the wire.
✔ The surface of the wire is not clean.
✔ The surface of the base material is not clean enough.
Protective Measure：
✔ Use a high purity protective gas.
✔ Welding is done with advance gas feed.
✔ Increase the protective gas flow rate appropriately.
✔ Clean the bevel and its edges of moisture, oil and gaseous film before welding.
✔ Protect the welding material and use high quality welding wire.
12 Problems of unsightly defects in weld forming
Detail Description：
The external dimensions of the seam do not meet the requirements, the residual height of the weld is not flat, the weld corrugation is shoddy, the longitudinal width is not uniform, the residual height is too high or too low, etc.
Causes：
✔ Unreasonable design of welding seam
✔ Unreasonable selection of welding parameters, mismatch of welding speed and current, and
✔ Uneven welding oscillation
✔ Uneven directionality of welding wire
Protective Measure：
✔ Select the right parameters such as welding current and speed when welding.
✔ Point the welding torch correctly.
✔ Use high quality welding wire
13. Welding slag defect problem
Detail Description：
Slagging is a condition in which slag or other impurities remain in the weld seam during the welding process.。
Causes：
✔ Welding current is too low.
✔ Molten pool temperature too low.
✔ Inadequate design of weld bevel size, incomplete cleaning.
Protective Measure：
✔ Select appropriate bevel size before welding.
✔ Clean the bevel and its immediate area as required.
✔ Select suitable parameters such as welding current and speed when welding.
14. Welding Arc Crater Defect Problems
Detail Description：
Refers to the formation of a depressed crater below the height of the weld at the general weld finish (weld termination), this small crater is known as the arc crater in technical terms
Causes：
Arc-off dwell time too short
Protective Measure：
Adjusting welding arc closing time and arc closing welding parameters
15. Welding spatter defect problem
Detail Description：
Refers to a portion of the molten metal of the wire flying outside the molten pool, flying outside the molten pool of metal is called spatter.
Causes：
✔ Insufficient purity of shielding gas.
✔ High impurities in the welding wire.
✔ The surface of the wire is not clean.
✔ The surface of the base material is not clean enough.
Protective Measure：
✔ Use a high purity protective gas.
✔ Weld with advance gas feed.
✔ Clean the bevel and its edges of moisture, oil and gaseous film before welding.
✔ Protect the welding material and use high quality welding wire.
16. Problems of poor welding arc starting defects
Detail Description：
Failed welding arc start, repeated arc start
Causes：
✔ Poor grounding of welder.
✔ The surface of the base material is not clean enough.
✔ Welding wire surface not clean enough.
Protective Measure：
✔ Check that all grounding sinks are good.
✔ Use slow start or hot arc start for easy arc starting.
✔ Use the gas pre-clean function.
✔ Conductive nozzle cavity is not blocked by metal material.
✔ Protect the welding material and use high quality wire.
17. Problems of welding arc instability defects
Detail Description：
Uncontrolled side-to-side oscillation or pulsation of the welding arc during operation.
Causes：
✔ Poor grounding of welder.
✔ Insufficiently clean surface of base material
✔ Wind is present in the workable environment.
Protective Measure：
✔ Check the conductive parts of the welder and keep the surfaces clean.
✔ Clean bevels and their edges of moisture, oil and oxide film before welding.
✔ Try not to work in environments that can cause sooting.
18. Problems of poor wire feeding defects in welding
Detail Description：
Welding wire in the process of sending out the conductive mouth intermittent, not out of the wire to burn the conductive mouth frequently.
Causes：
✔ Welding wire is worn and has a rough surface.
✔ Wire feed hose too long or too tight.
✔ Improper or worn wire feeder wheel.
✔ Welding wire is not pointing well.
Protective Measure：
✔ Lower wire wheel tension and use a slow start system.
✔ Check all wire contact surfaces and minimise metal-to-metal contact.
✔ Check the condition of the conductive nozzle and the condition of the wire feed hose and wheel.
✔ Check that the diameter of the nozzle matches the size of the nozzle.
✔ Check the wire disc for wear. Select a wire with a good surface quality and good pointing.
✔ Select the right wire feeder size, shape and suitable surface condition.