Effects of filler on the microstructure and corrosion of similar and dissimilar gas inert tungsten a

Time：2024-07-24 Click：

Abstract
Welding of dissimilar aluminum alloys has been widely used in many industrial applications. However, the selection of filler type still attracts significant interest in the welding research area. The present work concerns the effect of filler metal on the microstructure and corrosion of weld joints of dissimilar aluminum alloys. AA 5083 and AA 6082 alloys were welded by tungsten inert gas welding (GTAW) using filler metals ER 4043 and ER 5356. The microstructure observations and the corrosion test of the weld joints were carried out. Solidification cracks were observed in the ER 4043 weld zone, whereas defect-free joints were obtained using a mix filler welding process. A galvanic corrosion was observed on the boundary between the filler rod ER 4043 weld zone and AA 5083 base alloy. From the corrosion standpoint of view, the using of ER 4043 electrodes is not preferred for welding 5000 series aluminum alloys, whereas ER 5356 filler electrode is more favorable than ER 4043 filler electrode either for dissimilar welding of AA 5083 and AA 6082 alloys or individual welding of both aluminum alloys. No galvanic corrosion is observed between ER 4043 fillers and AA 6082 base alloy.
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Introduction
It is well known that Al alloys' fusion welding has different defects. The welding of the Al alloys defects includes pores, loss of particular elements, hot cracking, stress corrosion cracking, and mismatch between filler alloy and workpiece material; those reduce the weld strength1,2,3. The electrode selection during Al alloys' fusion welding affects the welding joint's properties and quality. Improper selection of welding electrodes affects aluminum alloys' corrosion resistance when used in marine or harsh environments. AA 5083 and AA 6082 represent two different families of Al alloys, namely the strained hardening alloys (AA 5083) and the heat-treatable alloys (AA 6082), which have good mechanical properties, corrosion resistance, and well workability and Weldability4,5,6.
The welding of aluminum alloys considered a difficult process due to its high thermal and electrical conductivity, thermal expansion coefficient, and refractory aluminum oxide (Al2O3)7. So, aluminum alloys gain thier strength through strain hardening, that missed during welding due to the recrystallization of grains. Moreover, the softening of the partially melted zone (PMZ) and the heat-affected zone (HAZ) and so grain growth in the fusion zone occurs8,9,10,11. However, the welded Al alloys strength and corrosion resistance can improved by controlling the size and distribution of intermetallics, such as Mg2Si, Al6Mn, and Al6 (Mn, Fe)10,11. Recent research has shown that incorporating nanomaterials, such as CNTs, TiO2, and Al2O3, in GTAW welding of Al alloys can improve the microstructure and mechanical properties while reducing welding defects12,13. Kumar. P. et al. and other researchers have reported that changes in welding parameters, such as welding current, speed, and heat input, can also affect the microstructure by altering the grain size and distribution of precipitates in the HAZ. Mustafa. U. et al. study the mechanical and corrosion properties of GTAW of aluminum alloys14.
Microstructures with fine grains at the weld zone was detected at the interfaces of ER 4043 filler wire in AA 6082 and AA 5083 alloys in different joints15. The fine grain structures observed in various areas contribute to increase the tensile strength of ER 4043 sealant welds15.
Welding AA 5083 and AA 6082 alloys attracted different previous works16,17. Bo Wang et al. modifies the ER 4043 filler electrode by adding Ti and Sr to improve the mechanical properties of AA 6082 weldments using GTAW16. They concluded that the addition of the Ti and Sr together improves the welded zone's microstructure and leads to the enhancement of mechanical properties. Moreover, Mohd Noor C. W. et al.17 studied the effect of the welding by GTAW and inert metal gas (MIG) welding on the microstructure and mechanical properties of AA 5083 welded joints used in shipbuilding. They found that fine microstructure was obtained for welded joints using GTAW, whereas coarse microstructure for welded joints used MIG. Also, the GTAW process gives welded joints high ultimate tensile strength and ductility compared with the MIG process.
In many cases, dissimilar welding of aluminum alloys becomes necessary. In this case, the problem of filler selection becomes more complicated due to the macrosegregation results from the inherent compositional variations between the filler and base metals18,19,20. Moreover, Aendraa Azhar Abdul Aziz et al.21 investigate the effect of different filler alloys on the mechanical properties and microstructure of welded AA 6061 aluminum alloy using MIG by two different fillers, ER 4043 and ER 5356. Aendraa Azhar Abdul Aziz et al. concluded that the amount of Si and Mg in the weld zone plays a vital role in controlling the microstructure and mechanical properties of the welded joints21. Che Lah et al.22 also studied the effect of fillers ER 4043 and ER 5356 on the porosity distribution of AA 6061 welded joints. The presence of Si and Mg in the weld zone was observed to affect the porosity distribution. However, no significant effect of the Si and Mg addition was observed on the hardness profile for both filler materials.
Aluminum and its alloys have numerous advantages, such as reducing structural weight and hull maintenance23. The 5xxx and 6xxx series alloys are widely accepted materials for shipbuilding due to their sufficient strength, good corrosion resistance, and ability to withstand corrosive atmospheres. These alloys used in construction of hull structures, superstructures, and decks of ships24. The alloying element of the 5xxx series include Mg, which provides good strength and outstanding corrosion resistance and toughness25. The 6xxx series alloys with the binary aluminum-magnesium silicide system (Al-Mg2Si) provides almost equal strength with slightly lower corrosion resistance than the 5xxxx series alloys25,26. These alloys commonly used for the construction of deck panels and marine frames of ships.
According to the problems noted while welding different alloys with different compositions using different electrodes27,28. The need for further investigations to overcome those problems is still needed. So, the current research aims to investigate the effect of using two welding electrodes, ER 4043 and ER 5356, simultaneously and individually for welding AA 6082 and AA 5083 using GTAW on the microstructure and corrosion resistance of the welded joints.
The present work will be undertaken to reach the following aims:
1.
Reach a proper selection of filler electrodes in welding similar and dissimilar AA 6082 and AA 5083 weld joints.
2.
Investigate the effect of the filler electrode material and base metal on the welding microstructure defects.
3.
Study the effect of single and multiple fillers in the weld zone on the corrosion resistance of similar and dissimilar AA 6082 and AA 5083 weld joints.
Materials and methods
The materials used in this research were wrought aluminum alloys 5083-H111 (AA 5083) and 6082-T6 (AA 6082) plates with a thickness, width, and length of 6 × 200 × 300 mm3. The chemical composition shown in Table 1 indicates that the AA 5083 and AA 6082 belong to the 5XXX and 6XXX series aluminum base alloys. The Mg and Si considered the main elements with high content after Al in the AA 5083 and AA 6082. The presence of the Mg in AA 5083 improves its strength, corrosion resistance, and weldability. Moreover, Si reduces melting temperature and improves fluidity.
Table 1 Chemical composition of materials (wt.%).
Full size table
Silicon alone in aluminum produces a non-heat-treatable alloy; however, in combination with Mg, turrn it into a precipitation-hardening heat-treatable alloys. Furthermore, both alloys contain reasonable amounts of Mn and Fe, those enhance the strength and significantly improve low-cycle fatigue resistance.
The Al plate edges prepared to have V-groove butt joined for using GTAW welding, as shown in Fig. 1, according to the American Welding Society (AWS) code D1.2/D1.2M27,29. ER 4043 and ER 5356 filler metals with chemical composition given in Table 1 are used in the current study. ER 4043 filler is suitable for welding heat-treatable base alloys, especially the 6XXX series alloys. It has a lower melting point and more fluidity than the 5XXX series filler alloys, and is preferred by welders because of its favorable operating characteristics. ER 4043 filler wires have a lower weld cracking sensitivity for 6XXX aluminum grades, which is a better option for welding than the ER 5356 filler wire. ER 4043 weldments can be used for service temperatures up to 65 °C (150 °F).