1 Overview
With the development of science and technology, light-weight and high-strength metal materials are increasingly used. Aluminum alloys have been widely used in aerospace , automotive and civil applications due to their low temperature characteristics, light weight and high strength. In the industry, it has become an important processing material. In order to meet the development of the modern aerospace industry, the defect-free connection of rust-proof aluminum 5A06 with good mechanical properties has become a modern development.
The aluminum alloy is easily oxidized in the air, and a dense refractory, relatively large oxide film is formed on the surface to hinder the oxidation of the base metal. In order to effectively remove the oxide film on the surface of the aluminum alloy and reduce the burning loss of the tungsten electrode, the welding aluminum alloy is often subjected to the method of alternating current TIG welding. Since the aluminum alloy is extremely oxidizable, in the actual production process, when the aluminum alloy is welded by the alternating current TIG welding method, the welding porosity defects are easily generated.
In this paper, the variable polarity pulsed AC arc welding power source is used to study the influence of pulse frequency and mixed gas ratio change on welding porosity defects, and satisfactory results are obtained.
2. Test conditions
Effect welding test object by welding experiment is to study the pulse frequency and rate of change of the mixed gas porosity defects in the weld.
The specifications of the welded test pieces are 390 mm × 240 mm × 1.5 mm and 390 mm × 84 mm × 1.5 mm, and the grade is 5A06. Use the wire of 5356f2mm. The composition of the sheet and wire is shown in Table 2. The welding gun nozzle is f10mm, the tungsten electrode is f2.4mm, and the welding fixture is made, as shown in Figure 1. When welding , the pressure plate is placed on the aluminum plate, and the pressure plate material is a phenolic laminated cloth board. The material has low thermal conductivity and does not lose heat generated when the aluminum alloy plate is welded . The aluminum alloy sheet required when welding conditions are consistent with models when a weld.
3. Influence of pulse frequency and mixed gas ratio change on weld porosity defects
(1) Pulse frequency change Before the butt welding of the test plate, the test plate weld shall be pickled, but the weld butt joint shall not be mechanically polished. The ratio of argon gas, alternating current frequency, welding speed, duty ratio, base current ratio and wire feed amount remained unchanged during welding . The welding tests were carried out on the pulse frequencies of 10 Hz, 50 Hz, 100 Hz, 150 Hz, 250 Hz and 350 Hz, respectively, and X-ray film inspection was carried out under the condition of ensuring penetration. The test parameters and X-ray film results are shown in Table 3.
It can be seen from the table that the tendency of the pores to be produced does not decrease as the pulse frequency increases, but at the intermediate frequency of 10 to 50 Hz, the tendency of the pores to be generated is the smallest (see Fig. 2). This is mainly because the pulse frequency is 10 to 50 Hz, the welding speed and the pulse frequency can be well matched, the shrinkage effect of the molten pool due to the change of the current is increased, the gas escape can be accelerated, and the gas is greatly reduced. The tendency of stomata to develop.
And when the pulse frequency reaches 100 Hz or more, the arc has been continuous during welding , the arc pointing force and the arc penetrating force are increased, and the current required for welding is reduced. Similarly, as the pulse frequency increases, the size of the molten pool gradually becomes smaller, and the size of the molten pool at a pulse frequency of 350 Hz is equivalent to 70% of the size of the molten pool at a pulse frequency of 10 Hz.
(2) Proportion of helium-argon gas The ratio of helium-argon gas is adjusted to 0:10, 3:7, 4:6, 5:5, 7:3, 10:0, and the 1.5 mm test plate is welded , at a guarantee of 1.5. In the case where the mm test plate is penetrated, the X-ray film is compared. The welding parameters and X-ray film results are shown in Table 4.
It can be seen from the table that the tendency of the pores to appear is not as small as the proportion of helium increases, but a minimum value occurs when the ratio of helium to argon is 4:6.
As the proportion of helium increases, the arc voltage increases correspondingly, the welding current decreases correspondingly, the arc stability increases, and the arc appears contracted. The size of the molten pool gradually decreases with the increase of the proportion of helium. When the shielding gas is pure helium, there is no problem of difficulty in arcing and difficulty in maintaining the arc. And when the shielding gas is pure helium, the weld pool is further reduced, and the size of the bath is half of that when the shielding gas is pure argon. The 13# to 16# plates were welded using the same welding parameters, and the same results were obtained after filming.
4. Conclusion
(1) When the pulse frequency is 10 to 50 Hz, the tendency of the generation of the welded pores is minimized for the thin aluminum alloy 5A06 welding .
(2) When the pulse frequency reaches 100 Hz or more, the arc during welding has been continuous, the arc pointing force and the arc penetrating force are increased, and the current required for welding is reduced.
(3) When the ratio of the helium-argon mixed gas is 4:6, the welding pores tend to be the least for the thin plate aluminum alloy 5A06 welding .
(4) With the increase of the proportion of helium, the arc voltage increases correspondingly, the welding current decreases correspondingly, the arc stability increases, the arc appears contraction, and the size of the molten pool gradually decreases with the increase of the proportion of helium.
Applying the above research results to the actual production of a certain type of aluminum alloy tank diaphragm weld, not only reduces the probability of weld porosity, but also increases the welding pass rate from 60% to over 90%.
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