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Article

Mechanical Properties and Tensile Failure Mechanism of Friction Stir Welded 2219-T6 and 5A06-H112 Joints

by
Jinghong Gu
1,
Wei Xue
2,3,* and
Diqiu He
4
1
State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China
2
School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China
3
State Key Laboratory of High Performance Complex Manufacturing, Central South University, Changsha 410083, China
4
Research Institute of Light Alloy, Central South University, Changsha 410083, China
*
Author to whom correspondence should be addressed.
Metals 2023, 13(3), 578; https://doi.org/10.3390/met13030578
Submission received: 16 February 2023 / Revised: 28 February 2023 / Accepted: 4 March 2023 / Published: 13 March 2023
(This article belongs to the Section Welding and Joining)
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Abstract

:
Friction stir welding was employed to weld dissimilar 2219/5A06 Al alloys in this work. The influences of alloy positioning on the mechanical properties and fracture behavior of the joints were studied via fracture morphology observation and microstructural analysis. The results show that the difference in the plastic flow and thermal field in the welding process is caused by different basic material configurations, which results in the formation of a free strengthening phase zone and microstructural heterogeneity in the joint. The low-hardness texture component caused by the free strengthening phase zone and microstructural heterogeneity becomes crack initiation, and a crack tends to propagate along the grain boundaries. Finally, when the stronger 2219-T6 alloy was placed on the advancing side, the joints had better tensile properties. The average tensile strengths of the 2A5R and 5A2R joints can reach 79.8% (343 MPa) and 78.4% (337 MPa) of the 2219 base material, respectively.

1. Introduction

Many spacecraft are widely constructed with aluminum alloys since they have high specific strength, corrosion resistance and formability [1,2]. With the development of aerospace science and technology, aerospace engines with high propulsion have recently attracted attention. Actually, the propulsion of rockets is provided by the propellant combustion of a combination of oxidizer and reductant, using the reverse thrust of gas flow. The propellant is mainly liquid organic compounds (the temperature is close to absolute zero), which requires the fuel tank to have good anti-rot performance and high strength at low temperature. Meanwhile, the temperature near the propellant combustion end is as high as 3300 °C, which requires the propellant conveying pipeline material to have a high strength at high temperatures. At present, the properties of a single aluminum alloy are inadequate for complex conditions. Therefore, the welding of structural parts for fuel tanks and delivery conduits may have to involve dissimilar aluminum alloys [3].
As a heat-treatable and aged Al-Cu alloy, 2219 alloy has high specific strength in the temperature range of −250 °C to 250 °C and is mainly used for high-load parts such as skeleton parts and skins of airplanes [4]. 5A06 alloy (Al-Mg) is a rust-proof aluminum with high strength, good corrosion resistance and weldability, and could be employed as a preferred material for liquid propellant storage [5]. In the 2219 and 5A06 alloys, Cu and Mg represent the major alloying elements, respectively, rendering fusion welding impossible, since Cu and Mg brought together in a liquid would result in low melting eutectic and solidification cracks. In addition, there are great differences between the components to be joined in their physical, chemical and mechanical properties [6], and the adoption of common welding processes (tungsten inert gas welding: TIG, laser beam welding: LBW, etc.) to weld them always leads to problems, including weld solidification cracking and low melting point element burning loss [7,8,9]. For instance, Li Heng et al. [10] welded a 5.5 mm-thick 2219-T87/5A06 H112 dissimilar aluminum alloy using the pulse VP-TIG welding method. The results indicate that the uneven structure near the weld fusion line negatively affected the mechanical properties of joints, and the tensile strength of the joint was only 63.6% and 75.3% of 2219 and 5A06 base metals, respectively. Chen et al. [11]. analyzed the crack propagation mechanism of TIG-2219/5A06 dissimilar aluminum alloy welded joints and found that the low-melting eutectic Al2CuMg phase that formed due to the obvious segregation of Mg and Cu in the weld became the main crack source, which adversely affected the strength and toughness of the welded joint.
Friction stir welding (FSW) has been proven to have great potential for joining dissimilar aluminum alloys [12]. Many efforts have been made to understand the microstructural evolution [12,13], material flow [14,15] and corrosion resistance [16,17,18] of FSWed dissimilar aluminum alloy joints. Asymmetric material flow and thermal field differences in the advancing side and retreating side of the nugget zone are intrinsic characteristics in the FSW process. Therefore, the base material configuration will greatly affect the material composition of the nugget zone and plastic metal flow behavior, which in turn influence the mechanical properties and corrosion behavior of the FSWed dissimilar joints. Tao et al. [19]. found that the evolution of the precipitated phase has great influence on the mechanical properties of the joint. The ultimate tensile strength (UTS) of the FSW 2060–T8 joints first increased and then decreased with increasing rotation rate or welding speed. It was found that the base material (BM) with lower solution temperatures, which is easily softened at higher temperatures, should be positioned on the retreating side (RS) where a lower temperature was detected [20]. Similarly, [21] indicated that when the BM with weaker mechanical properties was placed on the RS, a higher quality joint was fabricated. Hasan [22] believed that the tensile strength of FSW dissimilar 2021/7075 joints could be significantly improved when a BM with a higher thermal conductivity was located on the advancing side (AS). Many researchers have found that the heat-affected zone (HAZ) is usually located in the regions where the fracture takes place [23,24], which means the fracture behavior of FSW dissimilar joints is related to the base material location (AS or RS). Nevertheless, investigations on the fracture behavior of FSW dissimilar joints are still lacking. Additionally, most researchers have mainly focused on the improvement of FSW dissimilar 2XXX/7XXX joints, and the effect of the BM configuration on mechanical properties of FSWed dissimilar 2XXX/5XXX joints has not been seen in the open literature.
The objective of this work is, therefore, to identify the effect of BM configuration on the mechanical properties of the friction stir welded dissimilar 2219/5A06 joints and reveal its mechanism. The fracture behavior of tensile samples will be clarified via fracture morphology observation and microstructural analysis. The results obtained in this study will help pave the way for promoting the safe and reliable application of friction stir welded dissimilar 2XXX/5XXX joints in the aerospace industry.

2. Experimental Procedure

2.1. Material and Processing

The BMs used in this present study are 5A06 and 2219 aluminum alloys, whose chemical compositions (detected by the DF-1000D alloy component analyzer) are listed in Table 1. The dimensions of the sheets are 300 mm × 140 mm× 6 mm. This joint is known as the 2A5R joint, which consists of the 2219 aluminum alloy on the advancing side and the 5A06 aluminum alloy on the retreating side. Accordingly, the 5A2R joint is the joint in which the 5A06 and 2219 aluminum alloys are located at the AS and RS, respectively.
The welding operation was carried out on a vertical numerical control machine (Harms and Wende RPS100 refilled FSSW) (Harms and Wende, Hamburg, Germany). An FSW tool fabricated from H13 tool steel has a concave shoulder of 4.4° and a threaded, conical pin with three flat surfaces. The shoulder diameter is 14 mm, the pin diameter measures 3.4–6.0 mm and the pin length is 5.85 mm (measured from the outer edge of the shoulder). It has a 1 mm thread pitch and has three flats milled into the surface with a 0.6 mm constant depth. The schematic illustrations of the FSW are shown in Figure 1. It is worth noting that the sleeve and pin were maintained in the rotating state on the surface for 0.5 s to produce frictional heat at the beginning and end of the process so that the plunging force decreased gradually and the weld surface appearance improved.
Prior to welding, the plates were polished to remove the oxidation layer and any contaminants, and the surface was cleaned with anhydrous alcohol. Based on preliminary research, the welding speed selected for this work was 100 mm/min. The rotational speeds were 600, 800, 1200 and 1600 rpm.

2.2. Microstructure Characterizations

A cross section perpendicular to the welding direction was chosen to characterize the microstructure. After mechanical grinding and polishing, the specimens were etched with Keller’s Reagent (2 mL HF, 5 mL HNO3, 3 mL HCl and 190 mL H2O). Optical microscopy (OM) (OLYMPUS, VHX-5000 optical microscope, Tokyo, Japan) and scanning electron microscopy (SEM) (Zeiss, Supra 55, Jena, Germany) were employed. FEI Tecnai G2 F20 scanning transmission electron microscopy (STEM) (Field Electron and Ion Company, Hillsboro, OR, USA) was used to examine the precipitate morphologies. High-resolution TEM (HRTEM) (JEOL-1400Flash, Tokyo, Japan) image analysis was performed using the Digital Micrograph software package provided by Gatan Inc. (Pleasanton, CA, USA). As shown in Figure 2c, the peripheral part of the crack was cut by the wire cutting method, and some key positions were selected for slicing.

2.3. Static Mechanical Behavior

Tensile strength specimens were prepared according to the Chinese Standard GB/T228.1-2010, and their location and specific dimensions are illustrated in Figure 2a. For each test, three individual samples were used to ensure repeatability. The final result was the average of the three measurements. A Zwick Roell tester (ZwickRoell GmbH & Co. KG, Haan, Germany) was used to test the strength of the material, and the fracture surfaces were examined by scanning electron microscopy. Furthermore, the hardness of cross sections was assessed by a hardness tester (LECO, LM-247AT) (Huayin Test Instrument Co., Ltd., Laizhou, China) at 0.5 mm measurement spacing with a load of 0.3 kg applied for 15 s, as shown in Figure 2b.
Table 2 shows the tensile test results of joints under different welding process parameters. It should be noted that due to the obvious welding defects, it was not possible to conduct the test of welding joint tensile specimens at a rotation speed of 600 rpm. Table 2 shows that, in the welding process, the rotation speed and the configuration of the base metal on the forward or backward side have significant effects on the mechanical properties (tensile strength and elongation) of the joint, which is consistent with the views of published papers [6,25,26,27,28]. It is worth noting that under the same welding process parameters, when 2219 aluminum alloy is located at the forward side, the joint has stronger mechanical properties, and the fracture location of the tensile sample mainly appears in the HAZ region of the backward side. In contrast, when the 2219 aluminum alloy was located on the receding side, the mechanical properties of the joint weakened, and the fracture of the sample appeared in the transition zone of the NZ (nugget zone)/TMAZ (thermomechanically affected zone) on the receding side. This paper focuses on revealing the relationship between the positions of basic alloys and the mechanical properties of friction stir welded dissimilar 2219/5A06 joints, as well as the tensile fracture mechanism. The #1 and #2 joint specimens with good mechanical properties were studied in depth. The relevant analysis results are shown below.

3. Results and Discussion

3.1. Microstructure

The macrostructure morphology of the cross sections of the weld joints is shown in Figure 3. Figure 3a,b correspond to the 2A5R and 5A2R joints, respectively. As shown in the figures, the overall weld zone is “V” shaped. The upper part is roughly the same width as the diameter of the tool shoulder, while the lower part is almost the same width as the diameter of the pin. Three distinct zones develop on the basis of morphological characteristics, namely, the nugget zone (NZ), the thermomechanically affected zone (TMAZ) and the heat-affected zone (HAZ). In the welding process, the plastic flow direction of the AS is opposite to that of the RS, and the flow gradient on the AS is larger [29], resulting in clearer boundaries between the NZ and TMAZ on the AS side, as shown in Figure 3. The grains of the NZ are subjected to severe plastic deformation and thermal cycling and undergo dynamic recrystallization to form fine equiaxed grains [30]. At the same time, a classical onion-ring shape structure is observed in the NZ, and there are no holes or other defects, which indicates that the weld quality is ideal. Due to the high difference in heat input between the top and bottom layers of the welding area [30], the plastic flow capacity of the NZ is different, so two classical onion-rings are formed. Comparing Figure 3a,b, the width of TMAZ at the RS (~3000 μm) is significantly larger than that at the AS (~2000 μm) due to the more intense thermal-plastic rheology during welding. It should be noted that a narrow area containing the 5A06 alloy appears above the RS plate (2219 aluminum) at the weld (Figure 3b). The grains of the TMAZ were partially crushed and grew under the action of intense plastic deformation, while the rest were recovered and recrystallized under the action of the welding heat input cycle [30]. As shown in Figure 3c–h, the grains of the TMAZ are larger than those of the NZ. For the HAZ, a certain amount of growth resulted from the welding heat input.

3.2. Precipitates

There are various precipitated strengthening phases in the microstructure of 2219 and 5A06 aluminum alloys [4,5,10], and the evolution of the morphology and size of these precipitated phases significantly affects the mechanical properties of the alloys [30]. Figure 4 shows the TEM micrograph of the fracture location in the joints (along the <001> and <011> zone axes separately). As shown in Figure 4a,b, the precipitated phase is dominated by rod-shaped Mg5Si6 with a size range of 200~1200 nm (along the long axis). A few fine plate and round precipitates from Al6FeMn, Mg2Si and Al3Mg2 (<100 nm) are present, indicating the partial solution of these precipitates [31]. The reduced strengthening phase due to the solid solution increases the plasticity of the alloy but decreases the strength slightly [32].
In the 5A2R joint, there are many dispersive θ phases (Al2Cu) with a long axis size below 200 nm (along the <001> zone axis). Meanwhile, many uniformly distributed dislocation rings are found near the θ phase, as shown in Figure 4c,d. The fracture is located at the border of the NZ and TMAZ. Under the combined action of thermal cycling and mechanical agitation, the resolution phenomenon of the microstructure of the precipitated θ phase occurs, and the dispersion strengthening effect is weakened [4,32], resulting in a significant decrease in the strength and hardness of the fracture site.
Figure 5 shows the TEM micrograph of the lowest hardness on the RS. For the 2A5R joint, the minimum hardness occurs at the border between the NZ and TMAZ on the RS, and there is a significant free strengthening phase zone (FPZ) with a width of approximately 250 nm (Figure 5a,b). Additionally, there are many Mg5Si6 phases with round edges on the 5A06 side, and the size of the fine needle-like θ phase (homogeneous distribution) on the 2219 side is less than 150 nm. The θ phase disappeared in the TMAZ region near the AS-5A06 side of the 5A2R joint, and many dislocations and some rod-shaped precipitates occurred at the TMAZ near the 2219 plate, as demonstrated in Figure 5c,d.
Unlike the 2A5R joint, the rod-shaped Mg5Si6 phase in the NZ region near AS-5A06 of the 5A2R joint decreases in size and quantity, and no FPZ is found at the border between the NZ and TMAZ on the RS. The obvious differences of precipitate morphology and size at the weak border may lead to early fracture during tensile testing [30]. During this type of fracture, the metals situated on either side of the fracture path have a great difference in hardness, which results in a high yield strength [33].

3.3. Mechanical Properties of FSW Joints

3.3.1. Microhardness and Tensile Properties

The hardness of the welded joints (along the cross section) is shown in Figure 6. It is essential to locate the zero point in the center of the weld joint. The Cu element, as the major component for 2219 aluminum alloy, can refine grains and accelerate the progress of aging strength [4], so the microhardness of the weld near the 2219 BM is higher than that of the weld close to the 5A06 BM. According to the analysis in Section 3.1 above, in all dissimilar welding joints, the grains of NZ were fine equiaxed grains, which can effectively offset the softening effect of the plate during welding [30]. Consequently, the hardness of the NZ (108 HV0.3) is higher than that of the TMAZ (82~93 HV0.3). Due to the effect of the weld thermal cycle and plastic deformation [33], some grains of the TMAZ are elongated and coarsened, and its hardness (130 HV0.3) is slightly less than that of the 2219 BM (138 HV0.3). It has been reported that the precipitated phases are partly dissolved or coarsened resulting in the lowest hardness in the HAZ [30,33]. According to the Hall–Petch relationship, the reduction of hardness in the HAZ can be attributed to the coarsening of precipitates and grains due to the effect of the thermal cycle during welding, which resulted in a lower hardness than that of the BM. Based on the analysis in Section 3.2 above, it can be seen that the precipitated phase at the fracture has a partial solid solution, and the FPZ is formed. The FPZ lacks a dispersion strengthening effect and becomes the weak area of the welded joint [34]. As a result of large and abrupt variations in hardness, a weak transition occurs. In this region, there is a transition between alloy zone 2219 and alloy zone 5A06. The hardness of the NZ and TMAZ diminished with increasing thickness, and the lowest weld hardness (~80 HV0.3) occurred in the TMAZ of the RS. The hardness in the HAZ on the near 2219 side is 90~100 HV0.3, while the hardness near the 5A06 side is 80~90 HV0.3, as demonstrated in Figure 6a,b. Further analysis of the hardness in the NZ found that the softening zone size of the top region in the NZ is approximately 8~10 mm, and the counterpart in the bottom region in the NZ is approximately 5~7 mm, which is similar to the “V-shaped” morphology of the NZ in Figure 3.
In summary, FSW led to significant microstructural changes of 2219/5A06 dissimilar joints both across the weld and in the thickness direction. The initial second-phase particles along the grain boundaries of the BM were broken up into fine particles uniformly dispersed in the NZ where the grain size became considerably finer due to dynamic recrystallization [33]. The particles became even finer and grain size and hardness increased in the NZ along the thickness from bottom to top. Low hardness zones occurred in the TMAZ at the top and HAZ at the middle or bottom due to the presence of coarsened grains and particles.

3.3.2. Tensile Properties

Figure 7 and Table 3 show the tensile curves and elongation of the welded joint. The 2A5R joints have greater tensile strength and elongation at fracture than the 5A2R joints, but only to a limited extent. The strength coefficients of the 2A5R and 5A2R joints are 79.8% (343 MPa) and 78.4% (337 MPa), respectively, when compared to those of the BM of 2219. The elongation of the 2A5R and 5A2R joints is 81.6% and 51.4%, respectively, of that of the base metal of 5A06. In this work, when the stronger BM of 2219 is placed on the AS, it is beneficial for the mechanical properties of joints. These results are consistent with most research [35,36]. At the same time, it is known that the alloy positioning has a great influence on the heat inputs and the width of the softened zone during the welding process. Simar et al. [21]. found that a lower temperature was measured on the RS of dissimilar welds but not on the AS, which reduced the width of the softened zone at the RS. In this paper, the 5A06 alloy is susceptible to weakening due to welding. Therefore, when the 5A06 alloy is placed on the RS, the width of the softened zone is reduced, thus improving the tensile strength of the joint.

3.4. Fracture Analysis

Figure 8 shows the typical fracture locations of the 2A5R and 5A2R joints. The fracture positions of the joints are close to the RS, which exhibits a shear fracture of 45°. Figure 8a,c demonstrate two fracture modes, mode I and mode II. In mode I, failure occurred at the HAZ on the RS. In mode II, failure occurred at the boundary between the NZ and TMAZ on the RS, as shown in Figure 8b,d. There are three fracture zones (A, B and C) in the two fracture modes, as shown in Figure 8c,d. These zones correspond to crack formation zones, crack expansion zones and shear fracture zones. The 2A5R joint has a rougher fracture surface, and its proportion of zone B in the whole fracture area is higher (Figure 8c). The fracture surface of the 5A2R joint is bright, and the proportion of zone C in the whole fracture area is greater than that of the 2A5R joint.
Figure 9 shows the SEM micrographs of the fracture surfaces. There are many dimples and tearing edges in the fracture of the 2A5R and 5A2R joints, which is characterized by ductile fracture. There are many small dimples with uniform distribution in the fracture of the 2A5R welding joint, and most of the plastic pull-out holes are found, as shown in Figure 9a,b. Larger and deeper dimples are observed in the fracture of the 2A5R joint compared to the 5A2R joint (Figure 9c,d), indicating that the 2A5R joint has higher strength. However, the dimple is larger in size in the fracture of the 5A2R joints, and the presence of the dimple easily causes local stress concentration [15], as shown in Figure 9c,d. The grain size and precipitated phase at the fracture are responsible for this phenomenon [33]. There are long rod-shaped Mg5Si6 phases and fine Al6FeMn, Mg2S and other strengthening phases in the fracture of 2A5R (Figure 4), which can deflect and inhibit crack development and effectively promote the deformation capacity of the joint [5]. In the fracture of the 5A2R joint, grains are slightly elongated and coarsened compared with the BM of 2219, and the dislocation is obviously looped around the θ phase, which leads to local stress concentration and adversely affects the ductility of the alloys [37,38]. Therefore, the joint of 2A5R has better ductility (Table 3).

3.5. Crack Behaviors

The above analysis shows that there are obvious differences in the vertical microstructures of joint welds. The strengthening precipitates and grain size may play a dominant role in the crack initiation process. The precipitation state plays a decisive role in the hardness because the submicroscopic Al6FeMn, Mg2Si, Al3Mg2, Mg2Zn and θ precipitates give rise to a high hardness in the alloy [39]. Compared to the HAZ, the grains in the TMAZ and SZ undergo severe intense plastic deformation in addition to frictional heat; in particular, the SZ undergoes dynamic recrystallization, which induces the appearance of a fine equiaxed grain structure. Meanwhile, a larger amount of precipitate in the SZ was dissolved due to the higher temperature [30]. Hence, the hardness in the SZ and TMAZ can be attributed to the comprehensive effect of variations in the grain sizes and strengthening precipitates [33].
Microstructural heterogeneities, such as the precipitation of coarse particles along the grain boundary, continuous particles on the grain boundary and excessively wide of FPZs, have a great influence on the mechanical properties of the joint [40]. Based on many studies [40,41,42] on the effect of microstructural heterogeneity on the initiation and propagation of a crack, and combined with experimental results, a schematic diagram of the crack propagation mechanism of the 2219/5A06-FSW joint during the tensile process was proposed in this paper (Figure 10).
Finally, due to high differences in the thermal expansion coefficient and hardness, a residual tensile stress is generated at the border of the NZ/TMAZ or TMAZ/HAZ during postweld cooling [29], and then a crack tends to initiate at and propagate along the borders between the region with large grains (HAZ) or those with small grains (NZ/TMAZ) during the tensile test. The small grain boundaries may hinder the propagation of intergranular crack tips by causing crack closure (Figure 10b) whereas the large grain boundaries can change the propagation path of an intergranular crack (Figure 10c).

4. Conclusions

Through FSW, dissimilar welds between 2219-T6 and 5A06-H112 Al alloys were produced. A comparison of the mechanical properties and fracture behavior of the joints was carried out. The following conclusions were drawn:
(1)
Due to the difference in plastic flow and thermal field in the configuration of basic materials, the solid solution behavior of the precipitated phase in different areas of the joint changes, leading to the formation of FPZs and microstructural heterogeneity. Friction stir welded 2219/5A06 dissimilar joints with stronger tensile properties were obtained when the welding speed was 100 mm/min, the load-depth was 0.6 mm and the rotational speed was 800 rpm.
(2)
The mechanical properties of the joint showed higher values when 2219 Al alloys were placed at the advancing side. The average tensile strength of 343 MPa (2A5R joints) reaches 79.8% of that of the BM of 2219. The strength coefficient of the 5A2R joints is 78.4% (337 MPa) of that of the BM of 2219.
(3)
The formation of the FPZ and microstructural heterogeneity produced a low-hardness texture component at the border between the NZ and TMAZ. The border with the lowest hardness is the crack initiation for the friction stir welded 2219/5A06 dissimilar joints.
(4)
Regardless of the arrangement in the 2A5R joints or 5A2R joints, fracture occurs at the RS during the tensile test. A crack usually propagates along the borders of heterogeneous microstructure regions.

Author Contributions

Literature rearch, J.G.; figures, J.G.; writing, J.G.; study design, W.X.; data collection, W.X.; data analysis, D.H.; data interpretation D.H.; All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Key Research and Development Project of China (grant number 2019YFA0709002) and Postdoctoral Foundation of Central South University (140050079).

Data Availability Statement

Due to the nature of this research, participants of this study did not agree for their data to be shared publicly, so supporting data is not available.

Conflicts of 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.

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Figure 1. Schematic illustration of FSW process (a–c) tool pin profile.
Figure 1. Schematic illustration of FSW process (a–c) tool pin profile.
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Figure 2. Schematic diagram of tensile specimen (a), hardness test (b) and sections of the welded structure observed by metallographic examination (c) 2A5R, (d) 5A2R.
Figure 2. Schematic diagram of tensile specimen (a), hardness test (b) and sections of the welded structure observed by metallographic examination (c) 2A5R, (d) 5A2R.
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Figure 3. Micromorphology taken at different locations of welded joints (rotational speed of 800 rpm and welding speed of 100 mm/min). (a) 2A5R-joint, (b) 5A2R-joint, (c–h) correspond to the position in (a,b).
Figure 3. Micromorphology taken at different locations of welded joints (rotational speed of 800 rpm and welding speed of 100 mm/min). (a) 2A5R-joint, (b) 5A2R-joint, (c–h) correspond to the position in (a,b).
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Figure 4. Transmission electron microscopy micrograph of the fracture location in the joint (rotational speed of 800 rpm and welding speed of 100 mm/min): position 1 of 2A5R joint (a,b) and position 3 of 5A2R joint (c,d) from Figure 2c,d. HR-TEM (e,f) correspond to the selected diffraction pattern of (c,d).
Figure 4. Transmission electron microscopy micrograph of the fracture location in the joint (rotational speed of 800 rpm and welding speed of 100 mm/min): position 1 of 2A5R joint (a,b) and position 3 of 5A2R joint (c,d) from Figure 2c,d. HR-TEM (e,f) correspond to the selected diffraction pattern of (c,d).
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Figure 5. Transmission electron microscopy micrograph of the lowest hardness in the joint: position 2 of 2A5R joint (a,b) and position 4 of 5A2R joint (c,d) from Figure 2c,d.
Figure 5. Transmission electron microscopy micrograph of the lowest hardness in the joint: position 2 of 2A5R joint (a,b) and position 4 of 5A2R joint (c,d) from Figure 2c,d.
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Figure 6. Microhardness distribution of cross section of welded joint (a,c) 2A5R, (b,d) 5A2R.
Figure 6. Microhardness distribution of cross section of welded joint (a,c) 2A5R, (b,d) 5A2R.
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Figure 7. Stress–strain curves of the tree welding joint with one welding parameter (rotational speed of 800 rpm and welding speed of 100 mm/min): (a) 2A5R, (b) 5A2R.
Figure 7. Stress–strain curves of the tree welding joint with one welding parameter (rotational speed of 800 rpm and welding speed of 100 mm/min): (a) 2A5R, (b) 5A2R.
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Figure 8. Fracture location and macroscopic fracture surface morphology of tensile specimens (a,c) 2A5R, (b,d) 5A2R.
Figure 8. Fracture location and macroscopic fracture surface morphology of tensile specimens (a,c) 2A5R, (b,d) 5A2R.
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Figure 9. Fracture surface micrographs of the welding joint: (a,b) 2A5R, (c,d) 5A2R.
Figure 9. Fracture surface micrographs of the welding joint: (a,b) 2A5R, (c,d) 5A2R.
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Figure 10. Schematic diagram of crack propagation: (a) crack source, (b) small-grain zone, (c) large-grain zone. (b,c): Bar = 200 μm.
Figure 10. Schematic diagram of crack propagation: (a) crack source, (b) small-grain zone, (c) large-grain zone. (b,c): Bar = 200 μm.
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Table
Table 1. The chemical composition of alloys (wt.%).
Table 1. The chemical composition of alloys (wt.%).
ElementsCuMnMgZnTiZrFeSiAl
5A06-H1120.10.5~0.85.8~6.80.20.02~0.1–0.40.4Bal.
2219-T65.8~6.80.2~0.40.020.10.02~0.10.1~0.250.30.2Bal.
Table
Table 2. Mean tensile test results of FSWed joints (welding speed of 100 mm/min, 0.6 mm load-depth).
Table 2. Mean tensile test results of FSWed joints (welding speed of 100 mm/min, 0.6 mm load-depth).
NumberRotational Speed
(rpm)		Tensile Strength
(MPa)		Elongation Rate
(%)		Fracture Position
1#-2A5R80034319.70HAZ of RS
2#-5A2R80033712.40NZ/TMAZ of RS
3#-2A5R12002369.65HAZ of RS
4#-5A2R12002256.42NZ/TMAZ of RS
5#-2A5R160024310.21HAZ of RS
6#-5A2R16002327.64NZ/TMAZ of RS
Table
Table 3. Tensile properties of FSWed joints (welding speed of 100 mm/min, 0.6 mm load-depth and rotational speed of 800 rpm).
Table 3. Tensile properties of FSWed joints (welding speed of 100 mm/min, 0.6 mm load-depth and rotational speed of 800 rpm).
SampleUltimate Tensile Stress
(MPa)		Elongation Rate
(%)
BM5A0634024.13
221943012.23
Joints2A5R34319.70
5A2R33712.40
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Gu, J.; Xue, W.; He, D. Mechanical Properties and Tensile Failure Mechanism of Friction Stir Welded 2219-T6 and 5A06-H112 Joints. Metals 2023, 13, 578. https://doi.org/10.3390/met13030578

AMA Style

Gu J, Xue W, He D. Mechanical Properties and Tensile Failure Mechanism of Friction Stir Welded 2219-T6 and 5A06-H112 Joints. Metals. 2023; 13(3):578. https://doi.org/10.3390/met13030578

Chicago/Turabian Style

Gu, Jinghong, Wei Xue, and Diqiu He. 2023. "Mechanical Properties and Tensile Failure Mechanism of Friction Stir Welded 2219-T6 and 5A06-H112 Joints" Metals 13, no. 3: 578. https://doi.org/10.3390/met13030578

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