Microstructure and Mechanical Properties of Friction Crush Welded 1145 Aluminum Sheets with Flanged Edges

Abstract

The past two decades have witnessed prompt advances in aluminum alloy welding methods. Friction crush welding (FCW) has been recommended to be one of the key solutions to join these particular alloys with a range of plate thickness. This study aims to contribute to this welding technique by conducting several experiments to investigate the effect using three traverse speeds (120, 140, and 160 mm/min); and two rotational speeds (1400 and 1500 rpm) on the produces joint. These parameters were considered in a welding 1145 Aluminum sheets with 1mm thickness. The produced joints were evaluated using optical micrographs, micro-hardness, SEM, and tensile tests properties. The results showed that the best joint has 41 MPa tensile strength, 24 HV micro- hardness, and the best microstructure were obtained at 1400 rpm rotational speed and160 mm/min traverse speed.

Keywords:
(1145)Aluminum; Friction crush welding; Mechanical properties; Microstructure

1. Introduction

A dramatic increase in the metals alloys joining process has been seen in the last century. One of the most important processes is the friction welding, it has been widely used to produce almost defect free joint. It has been rapidly utilized by the jet engines, railways, automobiles and spaceship industry¹. Due to the need for defect-free and high-quality joints in recent decades, the welding defects formed during fusion welding were significant exciting research subject. The friction welding was an essential joining solution for aluminum alloys that has difficulty during welding². Recent developments in friction welding and friction stir welding have renewed the interest in inventing a new solid state joining method called Friction Crush Welding (FCW). The experience and in-depth knowledge gained from heat generated by high-pressure friction contact led to the development of FCW³. It is well known that the FSW process is an outstanding welding process for similar and dissimilar alloys. Nevertheless, tool wear in FSW was an essential issue, it affects the flow behavior particularly in the joint weld root and causes low stirring action due to tool degradation or self-optimization^4,5. Advances in FSW have allowed the researcher to overcome the tool wear issue and invent a new process for FCW to be used for the increasingly demanding weld sector.

A large amount of literature has reported the importance of the Aluminum alloys and its significant role that has been played in the traditional industrial sector and the military sector. This includes both various products that have been using in the infrastructures, automobiles, ships building, and aircraft. These particular alloys have a numerous applications due to their specific properties, such as machinability, a wide range of strength value and availability at a relatively affordable cost. In addition, Aluminum alloys have chemical stability and great metallurgical properties which leads to produce an efficient joint during welding in different joint techniques⁶. It has been documented that there is a wide range of alloys; some of them have an outstanding properties during different welding techniques. Whereas, some of these alloys are likely to produce some cracks and liquation during melting and solidification, which will affect the weld joint properties^7,8.

Unalloyed Aluminum belongs to the 1xxx series and has several applications, especially in the chemical and electrical fields. It is well-known that this particular alloy has good corrosion resistance, high electrical and thermal conductivities, excellent workability, and low mechanical properties. Its uses include packaging foil, heat exchangers, reflectors, electrical conductors, chemical equipment, decorative trim and architectural applications⁹. A schematic diagram of the FCW process that has been modified by Besler et al.¹⁰ is presented in Figure 1, it is able to produce sound joint for many alloy such as steel, Cu and Al alloys. The most important requirements for this process is the sheets edges, which need to be flanged at 90º with a particular height, and a specific gap between the edges. From Figure 1 it can be seen that the rotational disc has a profile which include disc shoulder and contour. It rotates with specific rotational speed while the work peace moves with particular traverse speed. This movement combination generates heat due to friction contact. After that edges gap will be filled by the crushed hot deformed materials. The obtained sound weld has almost more than 90% of the base metal yield strength¹¹. A number of research analyses have looked at the relationship between process parameters and the joint strength as shown below. A study by Besler et al.¹¹ did an experimental work using FCW, it employed additional metal wire in to weld gap of three different alloys which are joint separately (Steel, Al and CU). From the study a temperature distribution in weld zone was obtained. For all three alloys it has been concluded that a low distortion in joint can produced by considering low heat input with high speed of welding. In the microstructure of the steel joint a fine grain was obtained with 98 pct. On the other hand, Al and CU alloys weld joint showed bond strength value 77 and 69 pct for both alloys, correspondingly. An experimental effort was conducted by Brar et al.¹² to weld 304 stainless steel using FCW. A range of tool rotational velocity, travers speed, and FCW tool configuration were considered as process parameters, the ranges were specified using Taguchi method. The study reported that both weld residual stress and distortion were improved. According to this analysis of parameters, it was concluded that profile of the tool has been determined as a main factor that affects the joint bond strength, best strength was achieved at 740 rpm and 45mm/min rotational rate and traverse speed, respectively. Brar and Jamwal¹³ studied the effect of using spherical profile FCW disc on the joint strength for the 6061T-6 Al alloy. The study noticed that optimum bond strength of the weld joint was obtained at 740 rpm and 45 mm/min process parameters using the suggested tool profile. Their analysis revealed that this type of Al alloy was effectively welded using spherical tool configuration. An experimental investigation was conducted by Jomah et al.¹⁴ to explore the effect of using a range of process parameters on the mechanical properties and the microstructure of the oxygen-free copper joint. The investigated parameters included the rotational and traverse speeds; the range was from 220 to 1500 rpm and 20 to 150 mm/min correspondingly. The study reported that to improve the weld joint strength, the weld cracks must be reduced, and weld gap must be uniformly filled. In order to produced crack free joint surface; weld parameters need to be intensely investigated. Studies reported that speeds of 1500 rpm and 115 mm/ min could provide best joint with a 105 MPa tensile joint strength and 63 HV hardness. Jomah et al.¹⁵ reported a significant relationship between the height of the flanged edge the edge gaps. Three values of the height of the FCW flanged were considered to weld 1 mm thickness of Cu alloy. The results revealed that best value of the joint strength and hardness were found in case of considering 2.5 mm height and 0.5 mm flanged gap. It is worth to mention that the peak tensile strength value was reached to 115 MPa; also, they found both brittle and ductile fractures were revealed by using scanning electron microscopy (SEM) analysis.

Figure 1
A schematic illustration of the FCW process¹⁰.

Another study by Kumar and Brar⁸ developed a numerical modeling approach, using explicit transient finite element thermomechanical, on ABAQUS to predict the temperature distribution of copper and aluminum joints in the FCW. Johnson-Cook materials law was employed in the model to conduct the numerical investigations after it has been verified using experimental data.

In same field of study, it has been documented that friction welding technique has been wieldy and successfully conducted to join pipes^16-18, which showed a significant achievement in terms of defect free pipe joint for many alloys such Ti and steel. So far FCW has not been only applied for the metals sheets but also for the metals pipes; many attention has been paid to employing FCW to produce effective sound joint for the pipes welding^19-21.

There are quite a few research studies on FCW. However, studies on the process parameters of this welding technique are rare to find in the literature. Thus, more experimental work needs to be conducted to provide more insight into FCW process. In this current work an experimental investigation was conducted to examine the FCW processing parameters effect (tool rotational speed and feed rate) on the microstructure and mechanical properties of the 1145 pure Aluminum joint. Additionally, the failure mechanism of this particular joint has been investigated.

2. Experimental Work

In this current study 1145 Al alloy was considered as welded sheet. Two rectangular sheets with a dimension of 150 mm × 75 mm × 1 mm were chosen as base welded metal, they have a chemical composition shown in Table 1. A 90º angle was chosen to be a flange angle for the sheets with a 0.5 mm gap and 2.5 mm joint flanged height, the two sheets were adjacent to each other for welding using FCW as presented in Figure 1. A spherical profile FCW tool was selected, it made of A514/A517 grade R alloy steel which is essentially a type of high strength steel alloy, and the configuration of the considered tool is shown in Table 2. Process parameters of this welding trail are presented in Table 3. After the weld has been conducted, samples were prepared according to the properties that need to be investigated, which are the micro hardness and micro structure tests.

Table 1
The base material chemical composition.

Base Material	Chemical Composition (wt.%)
Al 1145	Al	Fe	Sn	Mn	Mg	Cr	Ni	Zn	Ag	Pb	Si	Cu
	Balance	0.379	0.005	0.04	0.007	0	0.007	0.04	0.002	0.005	0.116	0.05

Table 2
Geometrical properties of the FCW tool.

Tool Geometry	Specification
Tool/disc profile	Spherical
Material	High-strength low alloy steel
Diameter	80 mm
Width	8.5 mm
Shoulder(S)	2 mm
(Wc)	4.5 mm

Table 3
Specimen numbering and FCW process considered parameters.

Specimen Symbol	Rotational speed (rpm)	Feed rate (mm/min)
1	1400	160
2	1400	140
3	1400	120
4	1500	160
5	1500	140
6	1500	120

Welded samples were polished by polishing papers have a grade range of 150 to 2000 and then cloth polish was done. Etched process was then performed using Keller's Regent (1 ml, 1.5 ml, 2.5 ml, and 95 ml of HF, HCL, HNO₃, and distilled water, respectively). An average of three measurements of the micro hardness was taken; the test was done using a 0.9806 N load at different weld joint zones with a 20 sec dwelling time. Figure 2 shows the FCW tensile samples, a universal testing machine model WDW-200E was used to perform the tensile test according to the EN ISO 4136 testing standard. A high resolution SEM equipment type FEI 9922650 was utilized to examine the microstructure and the fracture of the surface.

Figure 2
Similar Al-Al tensile test specimens.

3. Results and Discussion

Figure 3 shows the weld microstructure of similar AL joint. Three weld zones are recognized in the Figure, they are formed during the FCW process and they have different grain size. Figure 3 shows the base metal (BM -a), while Figure 3-d the crushing zone (CZ -B) that formed due to the welding process is noticed. Due to the crushing process of the disk groove and the workpiece, extensive deformation will form and fill this gap.

Figure 3
Micrographs show the macro and microstructure of specimen 1 welded by FCW using a rotation speed of 1400 rpm and feeding rate of 160 mm/min.

Figure 3-c and -e show the thermodynamically affected zone (TMAZ), which is the main feature of the FCW process zone. It is formed due to the high plastic deformation caused by the mechanical effect of the tool. The main feature of this important zone is that it has a refined microstructure, which is formed due to the hot deformation and recrystallization that occurs during tool rotational and friction heating. The last zone that is formed during the welding process is shown in (Figuer.3b-f), it is identified as a heat-affected zone (HAZ). This zone is essentially formed due to heat that extended from the weld center zone and TMAZ, and it is formed without any mechanical effect.

Figure 4 (1-6) show the shape of the FCW weld with different feed rates and rotation speeds. It can be noticed that a good sound weld has been formed without any cracks or holes, and it seems to be uniform along the joint. By increasing the tool’s rotational speed from 1400 to 1500 rpm, the heat generated due to friction was increased. Consequently, the high deformation was seen as rotation speed increased from 1400 to 1500 rpm, as shown in Figure 4. Figure 4 (1) shows the bounded line that fills the gap between the two plates at a feed rate of 160 mm/min and 1400 rpm rotational speed . It is apparent from this figure, the selected process parameters led to produces a sufficient joint and the gap between the two sheets was fully filled.

Figure 4
Optical micrograph of FCWed Al-Al joints prepared using different rotational speeds and feeding rates.

Figure 4 (2-3) Shows that crack and micro-crack were formed probably due to the heat reduction resulting from the decrease in the feed rate

Figure 4 (4-6) shows an increase in the number of cracks, in addition to their length and width, which is due to the increased input heat and the tool rotation speed.

Figure 5 shows the profile of the Vickers micro-hardness in a direction transverse to the welding line. Also, it depicts the relationship between the hardness and the distance of the weld center for different welding process parameters. It can be seen from the figure there is a slight decrease in the hardness profile along the weld center. A value of 31 HV was reported at the base metal zone, reaching a range between 24 to 16 HV with different process parameters.

Figure 5
The distribution of the hardness profile along the Al-Al FCW joint at different tool rotational speeds and feed rates.

As mentioned previously, the defects may be the prime reasons for the hardness decrease in the CZ. The hardness of the CZ zone of weld 1 was 24 HV, which is the highest hardness. Welds 2 to 6 had hardness value of 21 HV, 20 HV, 19 HV, 17 HV, and 16 HV, respectively. The weld defects were cracks due to increased input heat because it increases tool rotation speed or decreases the generated heat because it decreases feed rate. These parameters may be the reason hardness decreases in the CZ.

Figure 6 noticeably shows the comparison between stress- strain curve of the base metal compared with six cases of welding considered in this study. In Figure 6 there is a clear trend of decreasing of the maximum value of stress which was noticed at 0.05 strain values. It reached to about 81 MPa, whereas it reduced by almost approximately 50% when it compared with case 1 of the weld. It can be argued this good sound weld that obtained in case 1 and 2 due to the process parameter of this cases have provided, equiaxed dynamic recrystallized grains with grain refining. This finding has been recognized as the main important advantage of using crush welding process.

Figure 6
Stress-strain curves of pure Al(1145)FCWed Al-Al joints using different tool rotational speeds, and different feed rates, measurement error (±3 to each curve).

The differences between cases1 to 6 are highlighted in this figure, it can be seen that the peak values of the tensile strength for cases 2 and 3 were about 30 MPa. On the other hand, for cases 4 to 6 the average value of strength was about less than 25 MPa. Due to the high rotational speed of the tool the input heat in the weld zone increases, which increases the weld zone cracks and weld defects. This could be the reason behind the reduction in strength.

The microstructure of crushed zones of the samples 1 and 6 are shown in Figure 7 , it presented the SEM micrographs. From the Figure 7 (1) it can be noticed a complete welding of the weld joint with some micro-crack width (1.5µm to 3.5µm), and a full gap filling between the aluminum sheets of crush zone. This is attributed to the increased feed rate that led to complete weldability. From Figure 7 (6) it has been concluded that as cracks found which mainly reported in this work a crack width from (7µm to 24µm) lead to a reduction in the weld quality.

Figure 7
SEM images in the CZ of Al-Al joints of specimens (1) 1400 rpm and 160 mm/min, and (6) 1500 rpm and 120 mm/min.

A fracture surface is seen in Figure 8 by using SEM micrographs of the FCW Al-Al joint of the specimen (1) at different regions. A cup and cone fracture been noticed, an elevated zone is shown, and the mode of failure was ductile fracture with large dimples. The large dimples come from the non-homogeneous structure of the little grains at the failure position and more significant plastic deformation.

Figure 8
Scanning electron microscopy images of the fractured surface after the tensile test of the Al-Al joint of the specimen (1) 1400 rpm and 160 mm/min.

4. Conclusion

In this experimental investigation, the intention was to assess the weld joint obtained by using FCW of similar Al alloy using a range of process parameters. The following conclusions are obtained from the current work:

1. 1

   A good sound weld was performed using FCW process to join similar metal of Aluminum sheets at feed rates 120 mm/min,140 mm/min, 160 mm/min and tool rotation of 1400 rpm, 1500 rpm.

2. 2

   According to optical micro-structural and SEM results; the rotational speed of 1400 rpm and the feed rate of 160 mm/min were the best operating parameters compared to other speeds.

3. 3

   It has been found that in case of increasing the tool rotational speed, a reduction in the joint strength and hardness occurs. However, the joint strength and hardness are increased when the feed rate is increased.

4. 4

   The evidence from this study suggests that by using toll rotation speed and feed rate of 1400 rpm and160 mm/min; best values of both hardness and strength which had a peak value of 24 HV, and 41 Mpa, correspondingly. Moreover, a ductile fracture mode was recognized under these operating parameters.

5. References

• ¹
  Singh P, Deepak D, Brar GS. Optical micrograph and micro-hardness behavior of dissimilar welded joints of aluminum (Al 6061-T6) and stainless steel (SS 304) with friction crush welding. Mater Today Proc. 2021;44:1000-4.
• ²
  Kah P, Rajan R, Martikainen J, Suoranta R. Investigation of weld defects in friction-stir welding and fusion welding of aluminium alloys. Int J Mech Mater Eng. 2015;10(1):1-10.
• ³
  Dinesh A, Ramakrishna VSMR. Friction crush welding: an innovative and cutting edge fabricating technology. In: National Conference on Research and Developments in Material Processing, Modelling and Characterization 2020; 2020 Aug 26-27; Jharkhand. Proceedings. Utraula: AIJR Publisher; 2021. p. 111.
• ⁴
  Hasan A, Bennett C, Shipway P. A numerical comparison of the flow behaviour in Friction Stir Welding (FSW) using unworn and worn tool geometries. Mater Des. 2015;87:1037-46.
• ⁵
  Hasan A, Bennett CJ, Shipway PH, Cater S, Martin J. A numerical methodology for predicting tool wear in Friction Stir Welding. J Mater Process Technol. 2017;241:129-40.
• ⁶
  Zandsalimi S, Heidarzadeh A, Saeid T. Dissimilar friction-stir welding of 430 stainless steel and 6061 aluminum alloy: Microstructure and mechanical properties of the joints. Proc ImechE L: J Mat Des Appl. 2019;233(9):1791-801.
• ⁷
  Kou S. Solidification and liquation cracking issues in welding. JOM. 2003;55(6):37-42.
• ⁸
  Kumar A, Brar GS. Numerical investigation of friction crush welding aluminium and copper sheet metals with flanged edges. In: E3S Web of Conferences. Proceedings. Hyderabad: EDP Sciences; 2021.
• ⁹
  Jomah A, Hashim F, Subhi A. Metallurgical investigation and mechanical properties of dissimilar friction crush welded Cu-Al sheets with flanged edge. J Phys Conf Ser. 2021;1973:012116.
• ¹⁰
  Besler FA, Schindele P, Grant RJ, Stegmüller MJR. Friction crush welding of aluminium, copper and steel sheetmetals with flanged edges. J Mater Process Technol. 2016;234:72-83.
• ¹¹
  Besler FA, Grant RJ, Schindele P, Stegmüller MJR. Advanced process possibilities in friction crush welding of aluminum, steel, and copper by using an additional wire. Metall Mater Trans, B, Process Metall Mater Proc Sci. 2017;48(6):2930-48.
• ¹²
  Brar GS, Singh M, Jamwal AS. Process parameter optimization of friction crush welding (FCW) of AISI 304 stainless steel. In: ASME International Mechanical Engineering Congress and Exposition. Proceedings. Washington, D.C.: American Society of Mechanical Engineers; 2017.
• ¹³
  Brar GS, Jamwal AS. Friction crush welding of aluminium alloy 6061 T-6. IJAMR. 2017;9(2):101-4.
• ¹⁴
  Jomah AS, Subhi AD, Hashim FA. Microstructure and mechanical properties of friction crush welded joints of oxygen-free Copper (C1020) Sheets. DJES. 2020;13(3):58-65.
• ¹⁵
  Jomah A, Subhi A, Hashim F. Effect of friction crush welding parameters on the properties of welded joints of C1020 copper sheet. J Phys Conf Ser. 2021;1973:012048.
• ¹⁶
  Beloshapkin G, Beloshapkin MV, Pisarov VK, Stolberov VE, Chernov VA. Friction welding of pipes. Weld Int. 2007;21(6):458-9.
• ¹⁷
  Vyas H, Mehta KP, Badheka V, Doshi B. Pipe-to-pipe friction welding of dissimilar Al-SS joints for cryogenic applications. J Braz Soc Mech Sci Eng. 2020;42(2):1-12.
• ¹⁸
  Palanivel R, Laubscher R, Dinaharan I. An investigation into the effect of friction welding parameters on tensile strength of titanium tubes by utilizing an empirical relationship. Measurement. 2017;98:77-91.
• ¹⁹
  Abdullah ME, Elmetwally HT, Yakoub NG, Elsheikh MN, Abd-Eltwab AA. Effect of orbital friction crush welding parameters on aluminum tubes. Int J Sci Technol Res. 2020;9:4483-6.
• ²⁰
  ElMetwally HT, Yakoub NG, ElSheikh MN, Abdeltwab AA, Abdullah ME. Influence of friction crush welding tool profiles on theweldability of commercial aluminum tubes. IJMPERD. 2020;10(3):5579-88.
• ²¹
  Joma A, Subhi AD, Hashim FAHA. Properties of welded copper tubes fabricated via friction crush welding. Eng Tech J. 2022;40(6):1-10.

Publication Dates

• Publication in this collection
  27 Feb 2023
• Date of issue
  2023

History

• Received
  17 Sept 2022
• Reviewed
  15 Jan 2023
• Accepted
  29 Jan 2023