Metal has a very distinctive feature is weldability. The so-called metal welding is a process that uses heating, high temperature or high pressure to produce molecules or atoms from two metal objects that are not together and united together. When it comes to metal welding methods are also characterized by diversity, the use of each method has its own advantages and disadvantages and different effects [1], which is attracting increasing attention.

　　1 Defects in the welding of metallic materials

　　1.1 The emergence of welding cracks

　　In the welding of metals, there is a relatively common situation is cracking, and cracking is mainly the difference between the crystalline state of the mutual changes that arise. The appearance of cracks is not very long, sometimes immediately visible or stop a moment that is visible, and its location is often in the welding base material and the junction of the fusion line, cold and hot is the main classification of cracks.

　　Hot cracking is basically occurs at the position of deviation. Its formation is mainly due to the impurity crystals left in the melt pool with low melting point and high freezing point and low strength, which are easily pulled apart when they are bound due to the many defects of these impurity crystals, which is the formation process of thermal cracking. In contrast to this cold cracking, first of all, in time on the hot cracking is late, during or after welding, and when the low temperature descends there will be cracks, and even some cold cracks appear time is more lagging, only after a few days, such a situation will be very easy to affect the normal use of structural safety

　　1.2 The emergence of non-welding, non-fusion phenomenon

　　When the metal is not all welded to the deepest part of the joint, that is, the root, resulting in the wood metal can not be completely melted away, thus causing is called not welded through, its main target is the wood. The disadvantages of this situation, which is not welded through, are numerous, frequently making the effective area of the weld gradually smaller and weakening the strength of the joint, and finally leading to a continuous decline in the fatigue strength of the weld. Another situation that is similar to unwelded is unfused, as the name implies, there is no perfect fusion between the metal joint, which brings the defect of reducing the bearing area, making it very difficult to gather stress

　　1.3 The appearance of slag situation

　　In the welding process there will be some residue left behind in the weld, we can call it in short slag. There are many reasons for the formation of slag, for example, when the current strength is not enough or large or small, welding speed or slow, unreasonable choice of welding rod, the bevel angle is not appropriate or the welding rod bias core and other reasons will make the edge of the weld left slag.

　　1.4 The appearance of other defects

　　(1) The weld organization may not meet the requirements, or because it fails to meet the standard chemical composition, and there is also the instability of the chemical composition of the weld metal caused by elemental burnout that occurs during welding. All of this will continue to weaken the mechanical capacity of the weld, thus more seriously making the corrosion resistance of the joint also suffered.

　　(2) Bite edge also occurs in the welding process, mainly due to high current or unsuitable welding rod angle reseal the weld edge of the crater is not well in the first time to fill the metal and caused. This phenomenon may make the use of metal materials greatly reduce the area, along with this also makes the structure to withstand the pressure resistance of this indicator is difficult to meet the requirements, more serious is due to the reaction force is greatly gathered and lead to cracks.

　　2 metal material welding in the prevention and control measures

　　All kinds of disadvantages are very easy to appear in the welding process of metal materials, so you have to worry about the quality of metal materials, it is clear that when we face these defects, timely and appropriate preventive and control measures are very necessary.

　　2.1 Measures to prevent cracking

　　Measures to prevent cracking are mainly the following: First, we must strictly comply with the rules associated with it, carefully consider the welding procedures you want to choose, strictly adhere to the standards of the welding rod, carefully identify its acidity and alkalinity, in order to achieve better results can be placed in a stable holding room, when we need to use it out; Second, we must carefully clean the interface to ensure that there is no moisture, oil or Is other traces left behind; Third, when we are during the welding, pay attention to choose a smaller current, and then choose multiple welding channels, a variety of levels to strictly enforce, so it is good to make the chance of cracking greatly reduced, but also to improve the shape of the weld wash, so that the stress of welding is also reduced.

　　2.2 Measures to prevent failure to weld through, failure to fuse

　　When welding has not yet begun, we have to do some preparatory work, such as a reasonable choice of bevel angle and size, the correct choice of the diameter of the welding rod. Secondly, the current size and welding speed should also be carefully selected. And in the process of welding, we should also pay attention to the proper swing of the chain above and concentrate on observing the changes on both sides. It must be ensured that all processes are carried out in accordance with the correct techniques and in compliance with the construction specifications.

　　2.3 Measures to prevent slagging

　　The first is to pay special attention to the selection of welding rods, the requirements of which are different for acidic and alkaline welding rods. The second is to have the right bevel angle and to control the welding speed that can not be too fast

　　2.4 Strengthening the skills of welders

　　Welding is also a certain technical requirements for welders, training in basic skills is necessary, the training content is mainly how to choose the materials to be used and the specific construction environment, and in the welding process should maintain what posture and control are also required to learn further, so that welding work is carried out smoothly without the influence of any external forces, so that the disadvantages can be further reduced. At the same time, the self-control of the welders needs to be further learned. At the same time, the self-control of the welders should be further enhanced, to make each welder qualified, the quality and skills of strict control.

　　2.5 Other comprehensive measures

　　In addition, we should also pay attention to other comprehensive measures, for example, for the construction environment should also be more requirements, if the temperature is relatively low, we must be certain heating of the materials used, in the construction area should also establish a certain clean area, but to ensure that during the work ventilation, for air humidity as far as possible to less than 90%, and to ensure that the concentration of argon gas to more than 99% and so on. A series of measures.

　　3 Conclusion

　　While the economy is developing rapidly, industry still occupies an important and indestructible position, which undoubtedly brings about the widespread use of metals, which increasingly has an important impact on daily production life. The popularity of metal has also led to the increasingly accelerated development of welding technology, however, through this article we can clearly understand that there are various disadvantages of metal welding, it will be directly to the detriment of the welded structure, or even serious harm to people’s personal safety.

Therefore, no matter what is its starting point, we have to overcome all the shortcomings to the greatest extent possible, the development and implementation of a variety of measures to put forward higher requirements for welders, and constantly develop better welding methods, so that the welding quality gradually climb.