Aluminum and aluminum alloy MIG welding, welding joints common defects are poor weld formation, cracks, pores, burn through, incomplete penetration, no fusion, slag inclusions.
First, poor weld formation
The difference in weld formation is mainly manifested in the corrugation of the weld seam, which is not beautiful and not shiny; the weld seam is not straight, varies in width and width, and the joint is too much; the center of the weld seam is raised, and both sides are flat or concave; the weld seam overflows.
1. cause
(1) Improper selection of welding specifications; (2) Incorrect torch angle;
(3) The welder is not skilled in operation; (4) The contact hole is too large;
(5) The welding arc is not strictly aligned with the center of the groove; (6) The welding wire, weldment, and protective gas contain moisture;
2. Preventive measures
(1) Select the appropriate welding specification for repeated debugging; (2) Maintain the proper inclination of the welding torch;
(3) Strengthen welder skill training; (4) Select suitable conductive nozzle diameter;
(5) Strive to align the welding arc with the groove; (6) Carefully clean the welding wire and weldment before welding; ensure the purity of the shielding gas.
Second, crack
Cracks in the welds of aluminum and aluminum alloys are produced during the crystallization of the weld metal and are called hot cracks, also known as crystal cracks. It has longitudinal cracks, transverse cracks (often extended to the base metal), and cracks in the roots, pits, and the like. Cracks will reduce the structural strength and even cause sudden damage to the entire structure, so it is completely forbidden.
1. cause
(1) The width-to-width ratio of the weld gap is too large; (2) the arc pit at the end of the weld seam cools rapidly;
(3) The wire composition does not match the parent material; (4) The operation technique is not correct.
2. Preventive measures
(1) Properly increase the arc voltage or reduce the welding current so as to widen the weld bead and reduce the penetration;
(2) Fill arc pits properly and use attenuation measures to reduce the cooling rate;
(3) Ensure that the wire and the base material are properly matched;
(4) Select the appropriate welding parameters, welding sequence, appropriate increase in welding speed, need to take preheating measures to warm up.
Third, stomata
In the MIG welding of aluminum and aluminum alloys, porosity is a common defect. It is very difficult to completely remove the pores in the weld. It can only be reduced to a greater extent. According to its type, the pores in the aluminum weld mainly include surface pores, diffuse pores, local dense pores, single atmospheric pores, root chain pores, and columnar pores. The porosity not only reduces the tightness of the weld, reduces the load bearing area of ​​the joint, but also reduces the strength and plasticity of the joint, especially the cold bend angle and impact toughness are reduced more and must be prevented.
1. cause
(1) Poor gas protection and impure protection gas; (2) Wire and weldment are contaminated;
(3) The humidity in the atmosphere is too large; (4) The arc is unstable and the arc is too long;
(5) The length of the welding wire is too long, and the distance between the nozzle and the weldment is too large;
(6) Improper selection of wire diameter and groove form; (7) Repeated arcing at the same site with too many joints.
2. Preventive measures
(1) Ensure gas quality, increase protection gas flow appropriately to eliminate all air in the welding zone, eliminate spatter at the gas nozzle, and ensure uniform protection of the airflow. The welding zone must have measures to prevent air flow, prevent air from invading the welding zone, and protect gas flow. Large, appropriate and appropriate reduction of traffic;
(2) Carefully clean the surface of the wire, weldment, oil, dirt, rust, scale and oxide film before welding, and use a wire with a high deoxidizer;
(3) Reasonably select the welding place; (4) Properly reduce the arc length; (5) Maintain a reasonable distance between the nozzle and the weldment;
(6) Select the thicker wire as much as possible, while increasing the blunt edge thickness of the workpiece, on the one hand can allow the use of large current, but also reduce the proportion of wire in the weld metal, which is effective for reducing the hole rate;
(7) Try not to repeat the arcing at the same site. When the boss starts to repeat the arc, it is necessary to polish or scrape the arc. If a weld is to be welded as long as possible after arcing, do not break the arc at will to reduce the joint volume. There must be a certain weld overlap area at the joint.
Fourth, burn through
1. cause
(1) The heat input is too large; (2) The groove is not properly machined and the assembly clearance of the weldment is too large;
(3) The solder joints have a large gap during solid welding, and a large amount of deformation occurs during the welding process;
The operation posture is incorrect.
3. Preventive measures
(1) Properly reduce welding current, arc voltage, and increase welding speed;
(2) increase the size of the blunt edge and reduce the root gap;
(3) Properly reduce the solder joint spacing during spot welding;
(4) In the welding process, the position of the welding torch must be correct and the operation must be skillful.
Fifth, incomplete penetration
1. cause
(1) The welding speed is too fast and the arc is too long; (2) The groove is not properly machined and the assembly clearance is too small;
(3) The welding technology is low and the operation posture is not properly grasped; (4) The welding specification is too small; (5) The welding current is not stable.
2. Preventive measures
(1) Properly slow down the welding speed and depress the electric arc; (2) Decrease the blunt edge or increase the gap of the main part;
(3) The angle of the welding torch is ensured to obtain a large penetration depth during welding, and the arc is always maintained at the front of the welding pool and must have the correct posture;
(4) Increase the welding current and arc voltage to ensure that the base metal has enough heat input to obtain;
(5) Increase the regulated power supply or avoid peak power usage.
Sixth, not fused
1. cause
(1) The oxide film or rust of the welding part is not removed; (2) insufficient heat input; (3) improper welding operation technique.
2. Preventive measures
(1) Carefully clean the surface to be welded before welding; (2) Increase the welding current, arc voltage, and reduce the welding speed;
(3) We must use the transport mode slightly when welding. There is a momentary stop on the face of the groove, and the welding wire is at the leading edge of the weld pool, improving the welder's technology.
Seven, slag inclusion
1. cause
(1) Incomplete cleaning before welding; (2) Excessive welding current leads to partial melting of the electric nozzle into the molten pool to form slag;
(3) The welding speed is too high.
2. Preventive measures
(1) Strengthen the pre-weld cleaning work. In multi-pass welding, the weld joint must be cleaned after each weld.
(2) In the case of ensuring penetration, the welding current should be appropriately reduced. When high-current welding, the contact nozzle should not be pressed too low;
(3) Properly reduce the speed, use a higher wire containing deoxidizer, increase the arc voltage.