Defects and Solutions of MIG Welded Joints of Aluminum and Aluminum Alloys

Defects and solutions of aluminum and aluminum alloy MIG welding joints

During MIG welding of aluminum and aluminum alloy, the common defects of welded joints mainly include poor weld formation, cracks, pores, burn through, incomplete welding, incomplete fusion and slag inclusion.

1. Poor weld forming

The poor formation of welding seam is mainly reflected in the unaesthetic welding seam ripple, and not bright; The welding seam is not straight, wide and narrow, too many joints; The center of welding seam is raised, both sides are flat or concave; Welds overflow, etc.
1. The reasons causing
Improper specification selection;
Incorrect welding gun Angle;
The welder is not skilled in operation;
The aperture of conductive nozzle is too large;
Welding arc is not strictly aligned with groove center;
Welding wire, welding parts and protective gas contain moisture.
2. Prevention measures
Repeated commissioning to select appropriate welding specifications;
Maintain proper inclination of welding gun;
Strengthen welder skill training;
Select the appropriate conductive nozzle diameter;
Strive to make welding arc and groove in strict alignment;
Carefully clean the wire and welding parts before welding; Ensure the purity of protective gas.

Second, the crack

Cracks in aluminum and aluminum alloy welds are generated during the crystallization process of weld metal, which is called thermal crack, also known as crystallization crack. They take the form of longitudinal cracks, transverse cracks (which often extend to the base metal), root cracks, arc-pit cracks, and so on. Cracks will reduce the strength of the structure and even cause sudden destruction of the whole structure, so it is totally not allowed.
1. The reasons causing
Excessive depth to width ratio of welding seam;
The arc pit at the end of welding seam cools quickly;
The welding wire composition does not match the base material;
Incorrect operation technique.
2. Prevention measures
Increase arc voltage or decrease welding current to widen weld bead and decrease weld depth;
Fill arc pits properly and adopt attenuation measures to reduce cooling speed;
Ensure reasonable matching of welding wire and base material;
Choose the appropriate welding parameters, welding sequence, increase the welding speed, need to take preheating measures to preheat.

Third, stomatal

Porosity is one of the most common defects in aluminum and aluminum alloy MIG welding. It is difficult to completely remove the pores in the weld, only to minimize the content. According to their types, the pores in aluminum welding joints mainly include surface pores, dispersion pores, local dense pores, single large pores, root chain pores, columnar pores, etc. Porosity can not only reduce the density of welding seam and bearing area of joint, but also reduce the strength and plasticity of joint, especially the cold bend Angle and impact toughness, which must be prevented.
1. The reasons causing
Poor gas protection, impure gas protection;
The welding wire and welding parts are contaminated;
Excessive absolute humidity in the atmosphere;
Arc instability, arc too long;
The welding wire stretches out too long and the distance between the nozzle and the welding parts is too large;
Improper selection of wire diameter and groove form;
Repeat arcing at the same location, too many joints.
2. Prevention measures
Ensure the quality of the gas, increase the flow of protective gas appropriately, in order to eliminate all the air in the welding area, eliminate splashes at the gas nozzle, so that the protective air flow is uniform, the welding area should have measures to prevent air flow, prevent air from invading the welding area, the flow of protective gas is too large, to reduce the flow appropriately;
Carefully clean up the oil, dirt, rust, scale and oxide film on the wire and the surface of the welding parts before welding, and use the wire with high deoxidizer;
Choose welding site;
When the arc length is reduced;
Maintain a reasonable distance between the nozzle and the welding parts;
Try to choose a thicker wire, while increasing the thickness of the workpiece groove blunt edge, on the one hand can allow the use of large current, but also to reduce the proportion of welding wire in the weld metal, which is effective for reducing the porosity;
Try not to repeat in the same part of the arc, repeat the arc to be polished or scraped clean; Once the arc of a welding seam should be as long as possible, do not break the arc at will, in order to reduce the amount of joint, there should be a certain seam overlap area in the joint.

Four, burning through

1. The reasons causing
Excessive heat input;
Improper groove processing, welding fitting clearance is too large;
The distance between solder joints is too large during point – to – point welding. Incorrect operating posture.
2. Prevention measures
Appropriately reduce welding current and arc voltage to improve welding speed;
Increase the size of blunt edge and reduce root clearance;
Properly reduce the solder joint spacing during spot bonding;
In the process of welding, the position of holding the welding gun should be correct and the operation should be skilled.

5. Incomplete welding

1. The reasons causing
Welding speed is too fast, arc is too long;
Improper groove processing and too small assembly clearance;
Low welding technology, improper operation posture;
The welding specification is too small;
Welding current is unstable.
2. Prevention measures
When slowing down the welding speed, lower the arc;
Reduce the blunt edge or increase the clearance of the main part;
Ensure that the Angle of the welding gun to obtain the maximum depth of fusion, arc always keep at the forefront of the welding pool, to have the correct posture;
Increase welding current and arc voltage to ensure sufficient heat input of base material;
Add voltage stabilizer or avoid peak power consumption.

Vi. Incomplete fusion

1. The reasons causing
The oxidation film or rust on the welding part is not cleaned;
Insufficient heat input;
Improper welding technique.
2. Prevention measures
Carefully clean the surface to be welded before welding;
Increase welding current, arc voltage and slow down welding speed;
When welding, a little way of moving the bar, there is a momentary stop on the groove surface, the welding wire in the pool front, improve the welder technology.

Seven, slag

1. The reasons causing
Incomplete cleaning before welding;
Welding current is too large, resulting in partial melting of the nozzle into the melting pool and slag inclusion;
Welding speed is too high.
2. Prevention measures
Strengthen the cleaning work before welding, when multi-pass welding, each weld shall also be cleaned up;
In the case of ensuring penetration, appropriately reduce the welding current, large current welding, conductive nozzle should not be pressed too low;
Reduce the speed appropriately, use the wire with higher deoxidizer, increase the arc voltage.