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aluminum. Study on Interfacial Morphology of Magnesium Alloy Magnetic Pulse Welding

magnesium. Aluminum alloy during the welding process of brittle Al-Mg intermetallic compounds, greatly reducing the performance of welded joints ... .... At present, such as diffusion welding, explosive welding, friction stir welding and other welding methods are inevitable will produce brittle A1. Mg intermetallic compounds. Magnetic pulse welding technology is a high-speed, solid, cold welding connection method, all the welding process will be completed in a very short time (microseconds), and the welding process does not need to add filler metal does not need to protect the gas, Affect the area, which can effectively prevent the joints at the coarse grain, can greatly reduce the interface of the intermetallic joint production [2]. The interface morphology of magnetic pulse welding is similar to that of explosion welding, usually showing three kinds of basic forms of waveform bonding region, direct bonding region and melting layer bonding zone. It is generally believed that the waveform-bound region is the ideal binding region. For the formation mechanism of interface wave, a series of studies have been carried out both at home and abroad. There are many mechanisms such as complex flow mechanism, vortex mechanism, Helmholtz instability mechanism and stress wave mechanism. At present, Israel's researchers Ben-Artzy and Stem through systematic research that: magnetic pulse welding interface is due to the stress wave caused by the loss of Helmholtz instability [3] caused. In this study, the Al-Mg dissimilar metal magnetic pulse welding test, the system discussed, analysis of Al-Mg dissimilar metal magnetic pulse joint interface morphology characteristics.

1 experiment

The MPW 20/9 magnetic pulse welding system provided by Israel PULSAR will be used for the welding test of aluminum and magnesium rods. In the test, 1060 aluminum alloy was selected as the outer tube, the outer tube was set to 16 mmxlmmx34 mm, the heat treatment state was O state, the inner rod was AZ31 magnesium rod, the heat treatment state was F state, the inner rod diameter was 11 mm, Performance is shown in Table 1. Welding with acetone before welding the surface to be welded parts, remove the surface oil and other impurities. In the test, MPW 20/9 magnetic pulse welding system was used to set different charging voltage (4,4.2,4.5 kV) for welding test. The weldment was tested by the detection method shown in Fig. 1a And the airtight performance of the weld parts of the test (Figure lb), the detection of joint bonding performance. The test results show that the welding consumables are not only good in airtightness but also have good bonding performance, and the fracture is broken at the base of the weldment. Will meet the above requirements of the welding parts for metallographic treatment and corrosion according to the national standard corrosion [41]. Using 4XC. 1 type optical microscope, HITACHI $ 3400N scanning electron microscope, Agilent G200 NANO INDENTER indentation instrument provided by the United States Agilent's joint interface after the microstructure, element distribution, energy spectrum components and hardness changes were analyzed in order to obtain Optimal interface.

 

2 Results and discussion

2.1 Optical microscopy

Charging voltage 4.3 kV 1060AI / AZ31Mg and charging voltage. Figure 2 shows the microstructures of the surface of the 5A03AI / 5A06AI weld at 2 kV. As can be clearly seen from Figure 2: A1. The amplitude of the interface of Al weld is basically symmetrical, and the corrugation is similar to that of sine wave. The phenomenon of periodic transmission is obvious, and the combination of the two materials is very dense. The interface of A1-Mg is a symmetrical sine Wave, embedded in the aluminum layer of the interface wave less; embedded in the magnesium layer of the interface wave more, forming an irregular wave-like combination. According to the stress wave caused by the Helmholtz fire mechanism, we can see that when the external force to A1-Mg two kinds of welding pieces together, because the Mg side texture is softer, shaping deformation ability, by external force extrusion , The g layer side of the first occurrence of instability. Compressive stress, the dislocation movement between the local grains is blocked, and the density of the dislocation plugs is increasing, resulting in the increase of the plastic deformation resistance between the grains in this region. When it exceeds the A1 layer Resistance to plastic deformation capacity, the instability of the state occurred in the Al layer side, this process as long as a little, Mg layer side of the compressive stress will be significantly reduced, and thus the dislocation of the plug group density also decreases, plastic deformation The ability to quickly recover, the Mg side of the re-emergence of instability, welding ripples and then into the Mg layer side, so repeated, so that the interface showed periodic irregular wave changes. In addition, the area indicated by A in Figure 2a is a "transition zone", which is distinct from the two base metal structures, and this region appears on the A1 side. Three different charging voltage test "transition zone" changes as shown in Figure 3. As can be seen from the figure, with the charge voltage decreases, near the weld "transition zone" has weakened the trend. When the charging voltage is 5 kV, it is clear that the entire welding interface is basically a large number of continuous distribution of the "transition zone", the thickest (Figure 3a arrow refers to) up to 32 ¨ m: the charge voltage is 4.5 kV, this area is intermittent, small distribution, and its thickness is about 0 p. M, much smaller than the charge voltage of 5 kV, only in Figure 3b arrows refer to the part of the relatively thick aggregation layer (26um); and the charge voltage of 4 kv, almost do not see the "transition zone."

 

2 2 Electron microscopy

Figure 4 is 1060AI / AZ31Mg weld interface "transition zone" structure and a good combination of elements at the interface line scan results. At the same time in this area to play spectrum points, accurate measurement of "transition zone" within the elements of the containing. Figure 4a in the interface between the two elements in the interface only a certain degree of diffusion. In the magnetic pulse welding process, close to the interface on both sides of the base metal at different times due to the instantaneous high pressure, high temperature caused by the plastic deformation of the atoms on both sides of the substrate must occur infiltration and convection, the final effect is the mutual diffusion between atoms The The "transition zone" in Figure 4b appears in the Al group. The results show that the content of Mg in this region is slightly higher than that of Al, and the content between them is in the same region, and the content of element is much different from that of AI Base side. Which is only from the perspective of elemental diffusion can not be explained, so it is speculated that this "platform" area must generate a new intermetallic phase. This is due to the magnetic pulse welding process in the improper welding process selection (charging voltage is too large), welding moment will produce a strong compressive stress will exceed the plastic deformation capacity of the metal itself, resulting in the interface area of ​​superplastic deformation, then a lot of pressure Stress generated by the load kinetic energy into heat accumulation in the welding interface, under the conditions of the adiabatic adiabatic, will make the interface near the part has been shaping deformation of the metal temperature rising to a certain temperature, there will be melting phenomenon, the formation of As indicated by the arrow in Figure 4b. So that the "transition zone" can be defined as a "melting zone". The results of EDS spectrum analysis of the "melting zone" (mass fraction,%) show that Mg is 5151, Al is 47 62 and Zn is 0 87. The data of the spectral spectrum analysis are consistent with the results of the element line scan, and the value of the element content and AI. Mg alloy phase diagram can be inferred that the intermetallic compound produced here is likely to be a mixture of A13M92 (40%) and AIl2Mgl7 (586%). The range of A13M92 is relatively narrow, and the range of Mg content is only 38.5% ~ 403%. The existence range of A112Mgl7 is wide and the range of Mg content is between 40% and 60%. Which can also explain the element line scan, why in the "melting zone" in the content of Mg elements are slightly higher than A1.

 

3 Conclusion

1) aluminum. Magnesium dissimilar metal magnetic pulse welding interface was irregular combination of corrugated morphology, embedded in the Al substrate side of the interface wave less.

2) The phenomenon of diffusion of atoms in the interface of magnetic pulse has a new hard brittle phase in the melting zone, and the new phase has a significant increase in the hardness of the melting zone.

3) The melting zone of the magnetic pulse welding interface appears on the A1 substrate side, and the size of the melting zone is related to the selected welding process parameters. Selection of appropriate welding process parameters can significantly reduce or even avoid the "melting zone" appears, significantly improve the weldability

 

 

 

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