To explore the influence of electrode positive/electrode negative (EP/EN) ratio on CMT advance-based wire arc additive manufacturing (WAAM) process for Al-Zn-Mg-Cu alloy, the behaviors of deposition process, the microstructure and mechanical properties of Al-Zn-Mg-Cu alloy WAAM are studied. The results showed that electrical waveforms and arc/metal transfer were unstable with a low EP/EN ratio, which deteriorated the stability of WAAM. The forming accuracy of deposited samples firstly increased with the EP/EN ratio ranging from 4:16 to 13:7, and then decreased if the EP/EN ratio continued increasing. In the inter-layer region, the samples showed a combination of columnar grains and pony-size equiaxed grains with an EP/EN ratio ranging from 4:16 to 10:10, while the size and quantity of equiaxed grains increased and the columnar grains almost disappeared with a higher EP/EN ratio (≥ 13:7). The enriched alloy elements in the grain boundary were easy to form large-scale precipitated phases, which were harmful to the mechanical properties. The microhardness distribution of all samples had the apparent fluctuation along the building direction due to the existence of the microstructure evolution and pores defect. This study proved that CMT advance process was a practicable and effective way for WAAM of Al-Zn-Mg-Cu alloy with optimal EP/EN ratio.
Research Article
Depositing Al-Zn-Mg-Cu alloy with different positive electrode/negative electrode ratios of CMT advance process
https://doi.org/10.21203/rs.3.rs-4645591/v1
This work is licensed under a CC BY 4.0 License
You are reading this latest preprint version
Wire arc additive manufacturing
Electrode Positive/Electrode negative ratio
Microstructure
Precipitated phase
CMT advance
Wire arc additive manufacturing (WAAM), a wire-based directed energy deposition (DED) approach using electrical arc as the fusion source, has been increasingly popular in industry and academia due to its capability of creating large-sized metal components with high deposition rate. As compared with traditional casting and forging methods, WAAM has significantly higher material utilization and manufacturing efficiency, as well as excellent production flexibility [1, 2], which makes it one of the most promising additive manufacturing technologies. To date, WAAM has been widely applied in processing various alloys including titanium alloys, aluminum alloys, steels, nickel-based alloys, and bimetals. It has been reported that Al-Si (4×××) [3, 4], Al-Cu (2×××) [5, 6], and Al-Mg (5×××) [7, 8] alloys has been successfully processed by WAAM. However, WAAM processed Al-Zn-Mg-Cu alloys (7×××) have not been reported for challenging issues such as turbulent melt pool and weld defects in welding. The cold metal transfer (CMT) process is a relatively new process developed based on gas metal arc welding (GMAW) technique, which is a short-circulating transfer process with little to no spatter, low heat input, high process tolerance, and excellent weld appearance [9–11] [12]. In recent years, various CMT technologies has been developed to process different aluminum alloys. Cong et al. [11] used conventional CMT, CMT pulse (CMT-P), CMT advanced (CMT-ADV), and CMT pulse advanced (CMT-PADV) to process Al-6.3%Cu alloys and found that aluminum alloys deposited by CMT-PADV process had the lowest porosity and finest equiaxed grain structure due to its lowest heat input. Zhang et al. [13] employed a different variant of CMT process, namely variable polarity cold metal transfer (VP-CMT) to fabricate Al-6Mg alloys parts and investigated the influence of different arc modes on their mechanical properties. The results showed that VP-CMT arc mode promoted columnar-to-equiaxed transformation with refined grain size, leading to improvements on mechanical properties. Zheng et al. [14] also found that VP-CMT arc mode processed aluminum alloys had fine equiaxed grains. These studies revealed that VP-CMT is the most suitable process to deposit aluminum alloy. Therefore, the CMT advance was considered as the best mode among all the CMT variants
Electrode positive (EP) to electrode negative (EN) ratio is a key parameter in conventional welding process. Therefore, EP/EN ratio may also play a critical role in VP-CMT process. Unfortunately, no report has been found on their influence on WAAM process. the CMT advance process, which was extensively investigated in welding process [15, 16], but rarely reported in WAAM process. In this paper, VP-CMP process of Al-Zn-Mg-Cu aluminium alloys (7×××) were optimized with a focus on the influence of EP/EN ratio. Specimens were deposited in single-layer and single-pass with different EP/EN ratios. Electrical signs and arc/droplet morphologies during the deposition were recorded to evaluate the stability of VP-CMT process CMT advance-based WAAM. Surface roughness of deposited specimens was measured to examine the geometric accuracy of deposit. Meanwhile, microstructural characteristics of the deposited materials including the phases of precipitates, morphology and orientation of grains were identified to reveal their correlation to mechanical properties. This study proved that CMT advance-based WAAM was a practicable and effective method for the fabrication of Al-Zn-Mg-Cu deposits with optimal EP/EN ratio.
As shown in Fig. 1a, the CMT-WAAM system used in this paper in composed of a Fronius CMT Advanced 4000 and an ABB robot. CMT advance mode was selected during the VP-CMT process, with electrical waveforms characterized by variable polarity. The feeding rate of wire was set as 6 m/min, and the deposition rate was 0.6 m/min. The shielding gas used in the process was 99.99% pure argon with a gas flow rate of 20 L/min. During the process, feedstock materials, i.e., ER7075 wires, were deposited on a substrate of the size 250.0 × 50.0 × 6.35 mm3, which was made of commercial 7075-T6 aluminum alloy. In order to evaluate the process stability at different EP/EN ratios, a National Instrument electric data acquisition system and a high-speed camera were used to record the electric signals and arc/droplet morphologies synchronously.
The fabricated materials were cut into specimens and etched at a mixed solution of fluoroboric acid and alcohol for metallography inspection. An optical microscopy (OM) was then used to observe the microstructures with the assistance of a polarizer. After binarization transformation, contour extraction, contour pixel coordinate transformation and other operations, the profiles of deposited samples were extracted to investigate the effect of EP/EN ratio on the forming accuracy. A scanning electron microscope (SEM, JSM-7800F) were employed to observe the distribution and type of precipitates at different regions of the samples, as shown in Fig. 1a.
In order to characterize the mechanical properties, specimens were cut from as-fabricated specimens along the deposition direction (Z axis) after natural aging at room temperature, as shown in Fig. 1b. Microhardness tests were then carried out a Vickers digital display microhardness tester (DHV-1000) with a load 200 g for a dwell time of 10 s. The distance between the two microhardness testing points was set to be 0.5 mm.
3.1 Stability and accuracy of process
In this paper, six different EP/EN ratios were used in the deposition process to understand their effects on the stability of WAAM process, as listed in Table 1, ranging from 4/16 to 19/1. Figure 2 showed the surface morphology of as-fabricated materials deposited in single-layer and single-pass, and at different EP/EN ratios. Evidently, discontinuous deposition was only observed at the lowest EP/EN ratio of 4/16. With the increase of EP/EN ratio, e.g., from 7/13 to 7/13, discontinuity of the deposited materials disappeared and corrugated fish-scale patterns dominated. With further increase of EP/EN ratio to around 19/1, i.e., significantly higher EP CMT cycles with substantially higher heat input, corrugated fish-scale patterns faded away due to improved wettability. Furthermore, it shall be noted that increasing EP/EN ratio led to significant reduction of voids and spatters during the deposition process. These results indicated that the electrical signals and droplet transfer of the above deposition process needed to be investigated.
| Test number | Case 1 | Case 2 | Case 3 | Case 4 | Case 5 | Case6 |
|---|---|---|---|---|---|---|
| EP/EN ratio | 4/16 | 7/13 | 10/10 | 13/7 | 16/4 | 19/1 |
Figure 3 showed the current/voltage waveforms of the VP-CMT process and the corresponding high speed camera recordings of arc/metal transfer at different EP/EN ratios. EN CMT cycles were characterized as a “cold” process, which had a lower heat input than that of the EP CMT cycles. With the decrease in EN CMT cycles, EN CMT cycles started to dominate the processing time. When the EP/EN ratio was 4/16, i.e., the process has the most EN CMT cycles, the wettability of the molten pool was deteriorated due to …, which contributed to the formation of higher liquid position. In the meantime, the molten pool with poor wettability cannot be spread to below the wire, resulting in difficulties direct transfer of droplets to the molten pool. Instead droplets moved to the unmelted substrate in wait phase, which prolonged the wait phase duration (Fig. 3a). The same phenomenon was observed in State 2, in which both the distance of wire feeding and wait phase duration in the first EP CMT cycle increased. With the prolonged current holding period, droplets grew to be oversized. and an additional projected droplet appeared in Fig. 3a before the normal short-circuiting transfer due to its large mass.
When the EP/EN ratio increased to 7:13, abnormal electric waveforms and metal transfer behavior deteriorated the process stability in Fig. 3b. As compared with the metal transfer behaviors in Case 1, the droplet in Case 2 was more likely to touch the molten pool instead of the unmelted substrate in shorting-circuit (SC) phase due to the more EP CMT cycles and higher heat input. The characteristics of electric waveforms and metal transfer behavior in Case 2 were: (1) A short SC phase duration appeared in Stage 3, as shown in Fig. 3b. The droplet grew in the wait phase and tended to move from opposite to along the travelling direction. When the droplet touched the molten pool, the SC phase started. Then the droplet continued to swing along the travelling direction, which caused a quick separation between the welding wire and molten pool and resulted in a short SC phase. (2) In Stage 4, due to the large viscosity of the molten pool, the separation between the wire and molten pool was hard to proceed at the last section of the SC phase. As a result, prolonged SC phase duration and several large spatters appeared in Fig. 3b.
To evaluate the forming accuracy of WAAM samples with different EP/EN ratios, the standard deviations of the contour lines in the stable part of the samples were measured. The standard deviation (S) was calculated as:
where n represents the number of coordinate points on the sample contour lines. yi and yj are the coordinate value and average coordinate value of the contour lines, respectively.
Figure 4 shows the macroscopic morphologies and statistical results of WAAM samples’ cross-sections under different EP/EN ratios. The average S first went down and then up with the increasing EP/EN ratio, and it had the minimum value of 0.141 when the EP/EN ratio was set as 13:7, which indicated optimal forming accuracy. The reasons for this phenomenon were: (1) The CMT advance mode had the characteristic of low heat input, dilution and high contact angle, especially in the condition with a low EP/EN ratio. Hence, the bead-shaped deposition appearance appeared in Fig. 4a, which significantly deteriorated the forming accuracy. (2) When the EP/EN ratio was higher than 13:7, the average S shows an upward tendency. The excessive heat input was achieved with a high EP/EN ratio, which strengthened the surface tension gradient of the molten pool and Marangoni convection. This strong convection induced the overflow phenomenon of the molten pool, which had a negative effect on the forming accuracy.
Meanwhile, when the EP/EN ratio was higher than 13:7, the stable current/voltage waveforms and deposition process occurred. As a result, the optimal forming accuracy with a stable deposition process was achieved when the EP/EN ratio was 13:7.
3.2 Microstructure
Figure 5 shows OM images of deposited samples under different Cases. Three special regions were focused in Fig. 5a, ie, top region, inter-layer region ,and inner layer region .The grain type was all distinguished as equiaxed grains in top and inner-layer regions as s the EP/EN ratio ranging from 4:16 to 19:1, while the grain size exhibited a growing trend. The high EP/EN ratio indicated more EP cycles and higher heat input, prolonging the duration of the liquid molten pool. Hence, the grains in the top and inner-layer regions with higher EP/EN ratios had a longer time to grow and coarsen. Additionally, the grain morphology in inter-layer region exhibited the characteristics of various grain types under different Cases. Firstly, when the droplet just touched the molten pool, the large undercooling was induced due to the highest temperature gradient. This large undercooling was conducive to the formation of pony-size equiaxed grains in the remelting zone. Then the columnar grains presented epitaxial growth at the transition region between the inter-layer region and inner-layer region. The temperature gradient decreased as the development of the columnar grain growth. Hence, the heat dissipation n and the grain growth directions turned to be random, which contributed to the transition from inter-layer region to inner-layer region. Meanwhile, with the increase of EP/EN ratio, the proportion of columnar grains in transition region decreased, while the proportion of pony-size equiaxed grains in remelting region increased. A combination of columnar grains and pony-size equiaxed grains appeared with an EP/EN ratio ranging from 4:16 to 10:10, and the columnar grains were almost missing with a higher EP/EN ratio (≥ 13:7). When the elevated EP/EN ratio were employed, the remelted area of deposited samples expanded and the temperature gradient of molten pool increased, thereby promoting the formation of equiaxed grains.
To further investigate the grain morphology and orientation of the CMT advanced-based WAAM Al-Zn-Mg-Cu alloy, the EBSD analysis of Case 4 also carried out, as illustrated in Fig. 6 regions. A located at the last deposition, where was free of remelting process. Region B was extracted from the stable area of the deposited samples. Figure 6a and c shows the inverse pole figures (IPFs) results of Regions A and B.The pony-size equiaxed grains, columnar grains, and coarse equiaxed grains occurred alternately along the building direction, which was consistent with the results of OM observation. The < 001 > orientation (red region), < 101 > orientation (green region), and < 101 > orientation (green region) in Regions A and B exhibited a uniform distribution, indicating a weak grain orientation. As a response, the values of the maximum multiples of uniform density (MUD) of Regions A and B were very low (2.07 and 1.62), according to the pole figures (IPF) results in in Fig. 6b and d. There are two reasons accounting for the low MUD values and weak grain orientation: (1) the CMT advance mode used in the WAAM process was characterized by the alternate transformation of EP and EN CMT periods, This rapid polarity change induced a stirring effect on the molten pool, contributing to the formation of a more random grain growth direction. As a result, the grain orientation became weak; (2) This strong turbulence in molten pool was conducive to break the dendrite and form more nucleation sites, thereby realizing the grain refinement. The average grain size of Regions A and B were only 48.36 µm and 51.31 µm, respectively.. The fine grains had a weaker grain orientation compared with that of columnar grains. Hence, the low MUD values and weak grain orientation of deposited sample were achieved by the CMT advanced-based WAAM process.
Al-Zn-Mg-Cu alloy is considered as a typical precipitation-strengthened aluminium alloy. and the precipitated phases play a crucial role in the mechanical property response, The coarse precipitated phases were generated massively during the deposition process, which distributed along the grain boundary and in the grain interior. as illustrated in Fig. 7. Meanwhile, the Zn, Mg, Cu alloy elements were enriched in these precipitated phases based on the map scanning results, which indicated that they may be the η Mg(Al, Zn, Cu) phases.., These coarse precipitated phases were easy to be the origin region of crack and harmful to the improvement of mechanical properties [17].
To identify the special type of these precipitated phases, the SEM images and corresponding EDS results were presented in Fig. 8. It was shown that the morphologies of the second phases varied little under different EP/EN ratios. Figure 8a and b shows low magnification backscattered electron (BSE) images of Cases 1 and 6. These net-shaped precipitated phases were continuously distributed along grain boundaries, forming a complex network. Meanwhile, many lamellar-shaped, net-shaped, cell-shaped, line-shaped and rod-shaped precipitated phases were mainly generated in the grain interior, as shown in Fig. 8c-f. To determine the chemical composition, EDS analysis was conducted on nine points within these precipitated phases. and the results are listed in Table 2. The majority of them contained a high content of Al, Zn, Mg, and Cu, indicating maybe they are η(Mg(Zn, Cu, Al)2)phases. The phase η in Al-Zn-Mg-Cu alloy was generally indicated as MgZn2, and the Zn atom was easy to be replaced by the Cu and Al atoms without changing the lattice structure [18], forming this solid solution Mg(Zn, Cu, Al)2 phases. Interestingly, the grey second phases (P3, P5, P9) had special grey values compared with other precipitated phases. Based on the EDS analysis, they were Fe-riched phases. The line scanning was also performed in Fig. 8i, the similar result indicated that the grey second phases may be Al7Cu2Fe. This Fe-riched phases with a high melting point were hard to be dissolved into the Al matrix [19], which were easy to be the initiation of the crack propagation [20].
What is more, the nano-scale precipitated phases were observed in the grain interior of bottom regions of WAAM samples (Cases 4 and 5), as shown in Fig. 8g and h. Instead, it almost disappeared in the top and middle regions of WAAM samples with the SEM analysis. Compared with the top and middle regions, the bottom regions of WAAM samples experienced the most reheating process, which could be regarded as a transient aging treatment, inducing the formation of more nano-scale precipitated phases.
| Position | Al | Zn | Mg | Cu | Fe | Possible phase |
|---|---|---|---|---|---|---|
| P1 | Bal. | 17.2 | 7.5 | 14.9 | -- | Mg(Zn, Cu, Al)2 |
| P2 | Bal. | 24.7 | 11.9 | 19.8 | -- | Mg(Zn, Cu, Al)2 |
| P3 | Bal. | 4.6 | 1.3 | 5 | 14.9 | Al7Cu2Fe |
| P4 | Bal. | 20.4 | 10.9 | 14.8 | 0.1 | Mg(Zn, Cu, Al)2 |
| P5 | Bal. | 5.3 | 1.6 | 5.8 | 15.4 | Al7Cu2Fe |
| P6 | Bal. | 13.8 | 5.9 | 8.2 | -- | Mg(Zn, Cu, Al)2 |
| P7 | Bal. | 17.2 | 8.1 | 14.2 | 0.1 | Mg(Zn, Cu, Al)2 |
| P8 | Bal. | 17.7 | 8.5 | 14.4 | 0.1 | Mg(Zn, Cu, Al)2 |
| P9 | Bal. | 4.5 | 1.4 | 6.7 | 19.6 | Al7Cu2Fe |
3.3 Mechanical properties
Figure 9 shows the microhardness distribution and statistical results of deposited samples under different EP/EN ratios. The micro hardness values of all samples were ~ 130 HV0.2, while it was slightly lower in Case 6 (EP/EN ratio = 19:1) due to the formation of the coarser grains. The micro hardness distribution of all samples had an apparent fluctuation along the building direction without a significant spike, which was unlike the results (first increased and then decreased) of samples in Ref. [20, 21]. Firstly, more was formed in this study due to its higher deposition speed (0.6 m/min) compared with that (0.1 and 0.15 m/min) in Ref. [20, 21]. The Zn element had a low melting point, which caused the evaporation of Zn elements and formation of Zn pores during the WAAM process. Hence, The WAAM of Al-Zn-Mg-Cu was easier to produce the pores than other series aluminium, especially under this high deposition speed (0.6 m/min) in this study. The appearance of more pore defects contributed to this fluctuant characteristic of micro hardness distribution. Secondly, Dong et al. and Qie et al. [20, 21] considered nano-scale precipitated phases difference led to the micro hardness distribution of WAAM Al-Zn-Mg-Cu alloy first increased and then decreased along the building direction. Instead, in this paper, the micro hardness specimens were treated by a long-time natural aging, which eliminated the difference in density and size of nano-scale precipitated phases along the building direction. In addition, as mentioned in Section 3.3, the pony-size equiaxed grains, columnar grains, and coarse equiaxed grains occurred alternately along the building direction, which also caused this fluctuant micro hardness distribution. As a result, the appearance of pores and the grain morphology difference contributed to this fluctuant micro hardness distribution. In our next step, the deposition speed and its matched wire feeding rate need to be further investigated to reduce the pore defect.
Additionally, the standard deviation of the Micronesian distribution first decreased and then increased as a whole as the EP/EN ratio increased from 4:16 to 19:1, as shown in Fig. 9. The minimum value was 4.67 when the EP/EN ratio was 13:7. The less EP CMT cycles and heat input were achieved with a low EP/EN ratio, which meant that the solidification rate of Cases 1 and 2 were higher than other Cases. The time for pore escape was less, inducing the formation of more pore defects. When the high EP/EN ratio (Cases 5 and 6) was used, the area and duration of the molten pool was increased, and the grains coarsening phenomenon appeared. Meanwhile, the equal gas flow rate was used in all Cases, the expanded molten pool increased the possibility of gas entering the molten pool. Hence, the number of pore defects was increased more under conditions of low or high EP/EN ratio, which caused the occurrence of high standard deviation of the microhardness distribution.
To optimize the EP/EN ratio during the CMT advance-based WAAM of Al-Zn-Mg-Cu alloy, the thin-wall components were manufactured under different EP/EN ratios. The process stability, forming accuracy, microstructure and mechanical properties were analyzed. The conclusions were as follows:
(1) When the low EP/EN ratio (< 13:7) was used, the abnormal droplet behaviors occurred easily, such as the additional projected droplet, large spatters, separation difficulty between the wire and molten pool and so on, which contributed to the unstable deposition process.
(2) High contact angle of molten metal was easily produced with a low EP/EN ratio (< 13:7), and a high EP/EN ratio (> 13:7) induced the overflow phenomenon of the molten pool by the strengthened Marangoni convection, which both had a negative effect on the forming accuracy of deposits WAAM components.
(3) The precipitated phases with different shapes were recognized as the η(Mg(Zn, Cu, Al)2) ,which distributed along the grain boundaries and in the grain interior. These large-sized precipitated phases were harmful to the mechanical performance enhancement of WAAM samples.
(4) The micro hardness distributions of all samples were fluctuant along the building direction, which were caused by the pores and the grain morphology difference. The deposition speed and its matched wire feeding rate should be improved in the further.Meanwhile, the standard deviation of the micro hardness distribution first decreased and then increased as a whole as the EP/EN ratio increased from 4:16 to 19:1.
Acknowledge
This work was supported by the National Key Research and Development Program of China (Grant No. 2022YFB4600902); National Natural Science Foundation of China (Grant No. 52075296); and the key research and development program of Shandong Province (Grant No. 2021ZLGX01).
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Data availability statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
- Tawfik MM, Nemat-Alla MM, Dewidar MM (2021) Enhancing the properties of aluminum alloys fabricated using wire + arc additive manufacturing technique - A review. J Mater Res Technol 13: 754-768. https://doi. org/10.1016/j.jmrt.2021.04.076
- Scotti FM, Teixeira FR, Silva LJ da, et al (2020) Thermal management in WAAM through the CMT Advanced process and an active cooling technique. J Manuf Process 57:23-25. https://doi.org/10.1016/j.jmapro.2020.06.007
- Köhler M, Sun L, Hensel J, et al (2021) Comparative study of deposition patterns for DED-Arc additive manufacturing of Al-4046. Mater Des 210:110122. https://doi.org/10.1016/j.matdes.2021.110122
- Gomez Ortega A, Corona Galvan L, Deschaux-Beaume F, et al (2018) Effect of process parameters on the quality of aluminium alloy Al5Si deposits in wire and arc additive manufacturing using a cold metal transfer process. Sci Technol Weld Join 23:316-332. https://doi.org/10.1080/13621718.2017.1388995
- Zhou Y, Lin X, Kang N, et al (2022) The heterogeneous band microstructure and mechanical performance in a wire + arc additively manufactured 2219 Al alloy. Addit Manuf 49:102486. https://doi.org/10.1016/J.ADDMA.2021. 102486
- Wang C, Li Y, Tian W, et al (2022) Influence of ultrasonic impact treatment and working current on microstructure and mechanical properties of 2219 aluminium alloy wire arc additive manufacturing parts. J Mater Res Technol 21:781–797. https://doi.org/10.1016/J.JMRT.2022.09.055
- Aldalur E, Suárez A, Veiga F (2021) Metal transfer modes for Wire Arc Additive Manufacturing Al-Mg alloys: Influence of heat input in microstructure and porosity. J Mater Process Technol 297:117271. https://doi.org/10.1016/J.JMATPROTEC.2021.117271
- Jiangang P, Bo Y, Jinguo G, et al (2022) Influence of arc mode on the microstructure and mechanical properties of 5356 aluminum alloy fabricated by wire arc additive manufacturing. J Mater Res Technol 20:1893–1907. https://doi.org/10.1016/J.JMRT.2022.08.005
- Pickin CG, Young K (2006) Evaluation of cold metal transfer (CMT) process for welding aluminium alloy. Sci Technol Weld Join 11:583–585. https://doi.org/10.1179/174329306X120886
- Gungor B, Kaluc E, Taban E, SIK Ş.Ş A (2014) Mechanical and microstructural properties of robotic Cold Metal Transfer (CMT) welded 5083-H111 and 6082-T651 aluminum alloys. Mater Des 54:207-211. https://doi.org/10.1016/j.matdes.2013.08.018
- Cong B, Ding J, Williams S (2015) Effect of arc mode in cold metal transfer process on porosity of additively manufactured Al-6.3%Cu alloy. Int J Adv Manuf Technol 76:1593-1606. https://doi.org/10.1007/s00170-014-6346-x
- Zhang, Y., Wu, L., Guo, X., Kane, S., Deng, Y., Jung, Y. G., ... & Zhang, J. (2018). Additive manufacturing of metallic materials: a review. Journal of Materials Engineering and Performance, 27, 1-13.
- Zhang C, Li Y, Gao M, Zeng X (2018) Wire arc additive manufacturing of Al-6Mg alloy using variable polarity cold metal transfer arc as power source. Mater Sci Eng A 711:415-423. https://doi.org/10.1016/j.msea.2017.11.084
- Zhang B, Zhang L, Wang C, et al (2019) Microstructure and properties of Al alloy ER5183 deposited by variable polarity cold metal transfer. J Mater Process Technol 267:167-176. https://doi.org/10.1016/j.jmatprotec.2018.12.011
- Xu P, Hua X, Chen N, et al (2020) Effect of the microstructure of IMCs and zinc accumulation on the mechanical properties of aluminum/galvanized steel joints in the VP-CMT process. J Manuf Process 58:894-904. https://doi.org/10.1016/j.jmapro.2020.07.050
- Mou G, Hua X, Shen C, Wang M (2020) Effects of thermal distribution strategy on a Ti-6Al-4V/304L dissimilar joint fabricated using the variable polarity cold metal transfer arc-brazing method. Mater Des 191:108619. https://doi.org/10.1016/j.matdes.2020.108619
- Fu R, Lu W, Guo Y, et al (2022) Achieving high strength-ductility of Al-Zn-Mg-Cu alloys via hot-wire arc additive manufacturing enabled by strengthening precipitates. Addit Manuf 58:103042. https://doi.org/10.1016/J. ADDMA.2022.103042
- Dong B, Cai X, Lin S, et al (2020) Wire arc additive manufacturing of Al-Zn-Mg-Cu alloy: Microstructures and mechanical properties. Addit Manuf 36:101447. https://doi.org/10.1016/j.addma.2020.101447
- Ma Z, Samuel AM, Doty HW, et al (2014) Effect of Fe content on the fracture behaviour of Al-Si-Cu cast alloys. Mater Des 57:366-373. https://doi.org/10. 1016/j.matdes.2014.01.037
- Qie M, Wei J, He C (2023) Microstructure evolution and mechanical properties of wire-arc additive manufactured Al–Zn–Mg–Cu alloy assisted by interlayer friction stir processing. J Mater Res Technol 24:2891–2906. https://doi.org/10. 1016/J.JMRT.2023.03.205
- Dong B, Cai X, Xia Y, et al (2021) Effects of interlayer temperature on the microstructures of wire arc additive manufactured Al-Zn-Mg-Cu alloy: Insights into texture responses and dynamic precipitation behaviors. Addit Manuf 48:102453. https://doi.org/10.1016/j.addma.2021.102453