There are many reasons for the formation. For some aluminum alloys containing more eutectic phases and impurities, cracks are easily formed during post-weld cooling. Since the linear expansion coefficient and the solidification volume shrinkage ratio of the aluminum alloy are relatively large, tensile deformation is likely to occur when the weld is cooled. In addition, in the process of cooling and solidifying, the aluminum alloy has liquid and solid metals in a certain temperature range, and the strength and plasticity of the aluminum alloy at this time are very low. In this temperature range, cracks are prone to occur, especially in the case where these conditions coexist, the occurrence of cracks is more serious. The presence of cracks creates stress concentrations that reduce the strength of the entire welded structure. For the inspection method of cracks, experienced staff can directly evaluate it visually. For the sake of safety, it can also be measured with a measuring ruler or X-ray.
For crack defects, we can take the following measures: First, select a suitable aluminum alloy to avoid the use of aluminum alloys containing more eutectic phase and impurities, and a modifier containing a small amount of refined grains in the aluminum alloy can be effective. Prevent hot cracks. Secondly, a welding method using a concentrated heating such as argon-arc welding by molten iron is used, and the welding method is effective for preventing crack generation. Thirdly, it is possible to weld the weld bevel or double-sided welding during welding, and also to adopt segment welding and pre-weld preheating, which can reduce the possibility of cracks in the weld.
Pores are prone to occur in aluminum alloy welding because hydrogen is present in the aluminum alloy weld and its solubility decreases with decreasing temperature. When the weld solidification time is short, the bubbles in the weld are too late to be discharged, and eventually the pores are formed. The presence of pores reduces the strength and ductility of the weld and also reduces the impact toughness of the weld. There are many factors associated with the formation of pores, such as average arc voltage, tip height, and welding environment. When the average arc voltage is low, it is easy to cause the arc to be unstable and splash, thereby destroying the weld balance and bringing in more hydrogen into the weld. The higher the height of the tip, the higher the temperature at the end of the wire, and the effect of the protection zone is weakened, thereby increasing the hydrogen content in the weld and easily forming pores. In addition, the external environment humidity also affects the formation of pores. For the inspection method of the pores, the pores of the surface can be visually inspected by means of a tool such as a magnifying glass. For the air holes in the weld, a compactness test or an X-ray test is required.
For stomatal defects, we can take the following measures: First, choose high input heat or increase the agitation of the molten pool, which can extend the welding time and allow the hydrogen to discharge the weld as completely as possible. Second, tungsten double-sided synchronous argon arc welding can be used. On the one hand, it can increase the protective effect of the shielding gas, on the other hand, it can stir the molten pool, avoid the entry of hydrogen, and at the same time discharge the hydrogen in the weld. Third, keeping the welding environment dry and cleaning and drying the welding groove can effectively avoid the generation of air holes.
Poor weld formation, undercut and slag inclusion
The main performance of poor soldering is that the center of the weld is higher than the two sides, and the entire weld surface is uneven and rough. The undercut will reduce the actual working area of the weld, which will easily lead to stress concentration and reduce weld strength. Welding and undercut defects are caused by improper welder operation. For example, if the welding voltage is too high and the welding speed is too fast, the above defects will be caused. For welding forming and undercutting defects, enterprises should improve the welder's welding skills and work quality, and strictly control the welding products. The occurrence of slag inclusion defects in welding is mainly due to the uncleanness of the weld bevel or the oxide contaminants generated by the welding wire. For the slag inclusion defect, the welding groove should be cleaned in time to control the welding environment and avoid impurities entering the weld. When inspecting the undercut, first use the main ruler against the side of the weld and then move the height ruler to just the other side of the weld. The measured height value is the amount of undercut, and the amount of undercut should be controlled according to the standard and actual needs.
Aluminum alloy welding with low density, corrosion resistance and high strength has a wide range of applications in various fields, but there are also some drawbacks. In this paper, the causes of defects such as cracks, pores, poor weld formation and undercuts are analyzed, and countermeasures are proposed. How to further improve the welding of aluminum alloy and ensure the quality of welding is still an important research direction.