Sharma, Lee, Ban, Shin, and Jung: Effect of Various Factors on the Brazed Joint Properties in Al Brazing Technology
Last few decades have seen a rapid increase in the fabrication and characterization of Al alloys for automobiles, heat exchangers and aerospace industries. Aluminium alloys are popular because of their high specific strength, light weight, excellent wear and high oxidation resistance. The development of aluminium alloys in these applications makes their study and research of utmost importance. Brazing is applied to the aluminium alloys for joining various aluminium parts together in most of the industrial applications. Various parameters affect the joining process of these aluminium alloys. In this article, various types of processing parameters have been discussed, and special attention has been given to the category of aluminium brazing alloys. The article reviews on the various parameters that affect the brazing property in various scientific and technological applications.
The brazing refers to the joining process of heating a joint to the liquidus temperature of the used filler metal over 450 °C, and below the solidus temperature of the base material. During this process, the base metals are not affected due to a lower brazing temperature than their melting points1,2)
. It should be also noted that brazing temperature is always lower than welding temperature. Though brazing is similar to the soldering procedure yet the temperatures involved are even lesser than in brazing process, i.e. <450 °C. However, the welding temperature of a filler metal may be significantly higher than the melting point of the base material3,4)
. Brazing provides a metallurgical bonding between the contact surfaces and the filler metal without melting the base metal3-5)
. There are various types of brazing processes such as dip brazing, induction brazing, laser brazing, resistance brazing, furnace brazing, and oxyacetylene flame brazing6-11)
. A summary of different types of joining processes in metallurgy is described in Fig. 1
Different types of metallurgical joining processes
A major advantage of brazing is that we can join dissimilar metals or ceramics with full perfection. There are various examples reported in literature where ceramic to metal joints are successfully brazed and investigated12-15)
. Direct or active metal brazing has been investigated where an active element like Ti or Zr is used in conjunction with the filler metal to wet the contacting surfaces. As a consequence, the need for conducting coating is minimized12)
2. Experimental steps in brazing
Brazing process generally composed of a series of steps depending on the joint to be brazed. The surface to be joined should be properly cleaned to avoid any defect in the brazed joint. The number of steps can be as follows:
Proper fit and clearance
Use of suitable flux (NOCOLOK flux etc.)
Fixing the two parts to be joined
Heating the parts to the particular brazing temperature
Cleaning of the joint to avoid the residues, if any
3. Brazing parameters
Brazing parameters play an important role in the brazed joint characteristics. All the brazing joint parameters should be dealt with great care to produce a fruitful joint. Some of the important brazing parameters can be classified as follows:
3.1 Brazing temperature
Brazing temperature is the most widely investigated parameter. Temperature has a strong effect on the final brazed strength and the corrosion properties. A high temperature can change the brazed joint morphology and even may cause softening, cracks generation, ultimately leading to the joint failure. For example, in the active metal brazing of Al2
/Cu joint with Ag-Cu-Zr-Sn filler, low brazing temperature is usually beneficial to maintain the superior bonding strength16)
. It is also reported that the interface thickness rises with the increase in temperature of silicon nitride joints using Ag-Cu-Ti-Mo filler metal under vacuum17)
. Yang et. al
. found that different types of reaction products are formed while brazing Al2
/Ti-6Al-4V with Ag-Cu-Ti-B filler. Different reaction products (i.e., TiCu, Ti(Cu, Al), Ti2
Cu and Ti2
(Cu, Al)) have their own growing speed towards the interface; which is a function of the brazing temperature, brazing duration and additive content, affect the overall joint strength directly18)
. Jiang et. al
. have found that the brazing of stainless steel (304 grade) to fins with nickel based filler, the strength is increased with brazing temperature. The microstructures in brazed joints are changed with brazing temperature and brittle phases are found to decline with the increase in brazing temperature19)
. For aluminium based applications, low melting point braze fillers are generally used in the literature. For example, the popular Al-Si filler has been consistently researched and developed. In a recent study, Sharma et. al
. incorporated ZrO2
nanoparticles in Al-Si-Cu filler to obtain improved joint properties as well as low melting point of the filler20)
3.2 Interfacial/multilayers at the interface
The formation of various interaction layers affects the brazed joint strength. It has been generally observed that interaction layers containing CuTi and Cu2
Ti are formed in Ti-6Al-4V/ZrO2
using an Ag-Cu-Sn-Ti filler 12,21-22)
. It has been already discussed that various multilayers or reaction products form at different temperatures. Generally, Cu2
Ti forms at low brazing temperature and increases at high temperature, thus imparting highest hardness value23)
. Therefore, a control of these reaction layers is important for achieving the best set of joint properties. A smaller thickness of these layers or IMCs corresponds to a higher brazed joint strength. An increase in the brazing temperature causes an increase in IMC thickness and vice versa24)
One of the very important criteria for any metal to be used as a filler in the brazing process is that it should wet and spread well over the contacting surfaces. Wetting can be defined as the ability of the molten filler metal to spread uniformly onto the surface of a metal after reflow procedure, and it should make a perfect bond with the base metal25)
. Figure 2.3 shows examples of wetting and de-wetting phenomena25)
Generally wetting depends on the wetting angle (θ) as shown in Figure 2
. The wettability is an important factor in brazing applications. The contact surfaces to be joined should be wet enough to make a bond and avoid any faulty joining. The addition of Sn, and Ti in Al-Si alloy improves the brazeability by increasing the fluidity of the filler alloy26-27)
. However, a high amount of Sn is not desirable as it may increase pitting and can be deleterious for the joints26)
. Magnesium is also an important element that is used to increase the wetting in some operations. It provides additional strengthening to the alloy and improves work-hardening rate in multiple brazing filler operations. Magnesium containing metal is assumed as candidate replacement for high strength alloys, or steel, primarily in view of the excellent elongation, toughness, as well as better working characteristics28-30)
Schematic diagram to show the wetting phenomena as a function of wetting angle
The wetting properties provided by the magnesium are generally due to the reaction of Mg with oxygen or moisture impurities as given by the following equations 31)
In the case of ceramic-metal brazing, wettability is a crucial factor due to poor wetting properties of engineering ceramics. It has been observed that the poor wettability of ceramic can be improved by using alloys such as modifiers and wetting promoters32)
. Various grain refiners such as, Ti, B, Sr, Na, Ca, P, Sb, Be, Ni, rare earth elements, oxides, etc. in brazing fillers are also added to increase the wetting and brazeability, and improve the quality of brazed joint and to produce minimum cracks and pores which may arise due to the non-uniform microstructures in Al-Si alloys33-39)
3.4 Manufacturing route
Various changes in the processing routes or employing an additional/sequential step may also reduce the cost and time. This can also affect the brazing microstructure as well as strength considerably. For example, the brazing of the extra pure Ti/Al2
joint brazed by the introduction of titanium hydride, the need for additional steps like metallization, electrodeposition and heating steps to the desired brazing temperature may be eliminated40)
Brazing in a vacuum is relatively economical method to provide a controlled brazing environment. It is an excellent way of protecting the workpiece from oxidizing agents as well as foreign impurities. The vacuum level generally used for this type brazing falls in the range ≈ 10-3
. Other commonly used atmospheres are nitrogen, hydrogen, argon, etc. It has been reported that the brazing under controlled nitrogen atmosphere reduces the amount of flux required (NOCOLOK flux) 41-42)
. Reducing atmospheres too prevent the formation of surface oxides and reducing the metal oxides during brazing1)
3.6 Overlapped width
It has been reported that the shear strength of brazed joints is highly dependent on the lap width to a greater extent. The brazed shear strength of the joints increases with the decrease in the lap width. Similar results are observed when the lap joint of a highly pure titanium plate to a low-carbon steel plate is obtained under a vacuum furnace using silver-based filler23)
. It is suggested to employ a lap width up to a maximum of thrice of the thickness of the base metal for a superior brazed joint strength23,43)
The effect of mechanical vibration also affects the strength of the brazed joint and the joining process. It has been reported that with an increase in vibration frequency from 0 to 400 Hz (and amplitude of 20 µm), the shear strength increases appreciably during induction brazing44).
3.8 Brazing duration
When the vacuum brazing of Ti-Al-based alloy to 40Cr steel using Ag-Cu-Zn filler is performed, it is observed that a change in brazing duration causes a change in brazing strength as well as a change in the joint microstructure and vice versa45)
. The brazing duration combined with the brazing time also affects the joint properties to a greater extent18,45)
3.9 Effect of different filler materials.
Many different varieties of filler alloys are available in brazing applications. Some of the brazing filler materials and their effects are tabulated below31)
4. Summary of the effect of different brazing parameters
Brazing is a technologically efficient process for the joining of the metal, nonmetals and ceramics to one another. Brazing has a wide promising future in automobiles, automotive, and aerospace industrial applications. More specialized methods are expected to emerge in future due to a vast development in the automotive and aerospace vehicles. Therefore, this paper throws a light on the effect of various parameters on the various brazing techniques and materials for a better understanding of the overall technological aspects. There are following conclusions that can be drawn from the present review.
Summary of the effect of additional elements in Al based brazing filler31)
Al-Cu, Al-Zn, Al-Mg etc.
Fluidity and brazeability improve. However, the formation of big Si needles is not desired due to crack generation problem.
Al-Si, Al-Zn, etc.
Improves age hardening mechanism, formation of GP zones, however CuAl2 is not good for a good brazing joint.
Al-Si, Al-Cu, Al-Zn, etc.
Work hardening, better corrosion resistance (less than 1wt% Mg is desired in brazing)
Al-Mg, Al-Cu, Al-Si, etc.
Increase in strength if added in minute quantities.
Al-Cu-Al-Si, Al-Mg, etc.
Ni enhances the elevated temperature strength and hardness.
Al-Cu, Al-Si, Al-Mg, etc.
Reduces friction, improves brazeability
Al-Cu, Al-Si, etc.
Ca, NA, Sr, P, S, Sb
Improves the morphology of the needle type Si and distributes the CuAl2 IMCs
Al-Cu, Al-Si, Al-Mg, Al-Si-Fe, etc.
Improves the corrosion resistance, morphology of iron complexes in the presence of Fe
Al-Si, Al-Cu-Fe, Al-Mg-Fe, etc.
Neutralizes the bad effects of Fe impurities and improves strength.
Al-Cu, Al-Si, Al-Mg, etc.
Depression of melting point, not desirable for heat exchangers due early to a quick vaporization nature.
Al-Si, Al-Mg, Al-Cu, etc.
Rare earth elements
Eutectic modification, refinement of microstructure
Al-Si, Al-Cu, Al-Mg, etc.
Refinement of microstructure, reduction of melting point, improvement of strength.
Temperature has a vital role in the brazing process. Increase in temperature improves the brazeability, however, it should not be too high to cause enough formation of IMCs that decreases the joint strength.
Brazing duration should be enough to cause a proper reaction between the joints otherwise the wetting will be poor.
Formation of interfacial layers is crucial for the brazing technology. Therefore, a strict control of IMCs is required via temperature or time optimization.
Agitation during the brazing process improves the shear strength of the joint by eliminating the impurities and cracks.
A proper lap width should be selected to exercise the maximum benefit of the brazed strength.
Manufacturing route also affects the brazing process. Brazing is different in vacuum and in inert atmospheres depending on the materials to be joined.
Wetting of the surfaces is also an important factor. The braze filler should have proper wetting, that is further dependent on the number of additional elements present in the filler. Therefore, a proper brazing filler with a proper amount of the additive is required.
This work was supported by the Energy Efficiency & Resources Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20142020104380).
1. Schwartz M.M, Brazing . 2nd ed. The Materials Information Society. ASM International; Ohio, USA: (2001)
2. Brazing Manual, American Welding Society, Committee on Brazing and Soldering. Reinhold Publishing Corporation; New York, USA: (1963)
3. Pritchard D, Soldering , Brazing , Welding . Crowood Press. (2001)
4. Kelly Ferjutz, Joseph R Davis. ASM Handbook:Volume 6:Welding, Brazing, and Soldering. 10th ed. ASM International; (1993)
5. O'Brien R. L. Welding Handbook: Welding Processes, 2, Welding Handbook. 8th ed. American Welding Society; (1991)
6. Woods R. A, Robinson I.B. Flow of Aluminum Dip Brazing Filler Metals. Weld. J. Res. Suppl. 440s–445s (1974)
7. Daly B. Basics of Brazing With Induction Heating. Weld. J. 52–54 (2013)
8. Riedelsberger H. Laser Brazing in The Automotive Industry. AWS Welding Show Atlanta. (2006)
9. Steinmeir D. Resistance Brazing Basics. Microjoining solutions; Arcadia, CA: (2003)
10. Introduction to Furnace Brazing, Air Products, Air Products and Chemicals, Inc. (2001)
12. Kee S.-H, Park S.-Y, Heo Y.-Ku, Jung J.-P, Kim W.-J. Brazing Characteristics of ZrO2 and Ti-6Al-4V Brazed Joints With Increasing Temperature. J. Kor.Acad. Prosthodont. 50 (2012), 169–175 (in Korean)
13. Zhang J. X, Chandel R. S, Seow H. P. PTLP Joining of Al2O3-Stainless Steel 304 Using Ni-Cr Foil—The Microstructure Morphologies of Joint Interfaces. Mater. Manuf. Proc. 18 (2) (2003), 181–193
14. Singh M, Ohji T, Asthana R. Ceramic Integration and Joining Technologies:From Macro to Nanoscale, American Ceramic Society. New Jersey: John Wiley and Sons; (2011)
15. Singh M, Shpargel T.P, Morscher G.N, Asthana R. Active Metal Brazing and Characterization of Brazed Joints in Titanium to Carbon-Carbon Composites. Mat. Sci. Eng. A
. 412 (1-2) (2005), 123–128
16. Kim J.-H, Yoo Y.-C. Bonding of Alumina To Metals With Ag-Cu-Zr Brazing Alloy. J. Mat. Sci. Lett
. 16 (1997), 1212–1215
17. He Y. M, Zhang J, Wang X, Sun Y. Effect of Brazing Temperature on Microstructure and Mechanical Properties of Si3N4/Si3N4joints brazed with Ag-Cu-Ti +Mo Composite Filler. J. Mater. Sci. 46 (2011), 2796–2804
18. Yang M, He P, Lin T. Effect of Brazing Conditions on Microstructure and Mechanical Properties of Al2O3/Ti-6Al-4V Alloy Joints Reinforced by TiB Whiskers. J. Mater. Sci. Technol. 29 (2013), 961–970
19. Jiang W, Gong J, Tu S.T. Effect of Brazing Temperature on Tensile Strength and Microstructure For A Stainless Steel Plate-Fin Structure. Mater. Des
. 32 (2011), 736–742
20. Sharma A, Roh M.H, Jung D.H, Jung J.P. Effect of ZrO2 Nanoparticles on The Microstructure of Al-Si-Cu Filler For Low-temperature Al Brazing Applications, Metall. Mater. Trans. A. 47 (2016), 510–521
21. Kee S.H, Xu Z, Jung J.P, Kim W.J. Joining of Ceramic and Metal Using Active Metal Brazing. J. Microelectron. Packag. Soc. 18 (3) (2011), 1–7 (in Korean)
22. Liu Y, Hu J, Zhang Y, Guo Z, Yang Y. Joining of Zirconia and Ti-6Al-4V Using A Ti-Based Amorphous Filler. J. Mater. Sci. Technol. 27 (2011), 653–658
23. Elrefaey A, Tillmann W. Interface Characteristics and Mechanical Properties of The Vacuum-Brazed Joint of Titanium-Steel Having A Silver-Based Brazing Alloy. Metall. Mater. Trans. A
. 38 (2007), 956–2962
24. Kim H.-J, Lee J. Y, Paik K.-W, Koh K.-W, Won J, Choe S, Lee J, Moon J.-T, Park Y.-J. Effects of Cu/Al Intermetallic Compound (IMC) on Copper Wire and Aluminum Pad Bondability. IEEE Trans. Comp. Packag. Manuf. 26 (2003), 367–374
25. Kogi S, Kajiura T, Hanada Y, Miyazawa Y. Wetting and Spreading Behavior of Molten Brazing Filler Metallic Alloys on Metallic Substrate. IOP Conf. Series:Mater. Sci. Eng
. 61 (2014), 012017
26. Li J, Liu Y, Tan Y, Li Y, Zhang L, Wu S, Jia P. Effect of Tin Addition on Primary Silicon Recovery in Si-Al Melt During Solidification Refining of Silicon. J. Cryst. Growth
. 371 (2013), 1–6
27. Zor S, Zeren M, Özkazan H, Karakulak E. Effect of Titanium Addition on Corrosion Properties of Al-Si Eutectic Alloys. Prot. Met. Phys. Chem. Surf
. 48 (2012), 568–571
28. Aucote J, Evans D.W. Effects of Excess Silicon Addition on Ductility of Al-0.95% Mg2Si Alloy. Mat. Sci. Technol. 12 (1978), 57–63
29. Dahle A.K, Nogita K, McDonald S.D, Dinnis C, Lu L. Eutectic Modification and Microstructure Development in Al-Si Alloys. Mat. Sci. Eng. A
. 413–414 (2005), 243-248
30. Polmear I.J. Light alloys From Traditional Alloys to Nanocrystals. 4th ed. Elsevier-Butterworth Heinemann; (2006)
31. Sharma A, Shin Y.S, Jung J.P. Influence of Various Additional Elements in Al Based Filler Alloys For Automotive and Brazing Industry. J. Welding and Joining
. 33 (5) (2015), 23–30 (in Korean)
32. Calliari I, Ramous E, Brunelli K, Favaron P. Characterization of Vacuum Brazed Joints for Super-conducting Cavities. Microchim. Acta. 147 (3) (2004), 141–146
33. Ware T. N, Dahle A. K, Charles S, Couper M. J. Effect of Sr, Na, Ca & P on the Castability of Foundry Alloy A356.2. In: ASM Materials Solutions, 2002 Conference & Exposition, 2nd International Aluminium Casting Technology Symposium; Columbus, Ohio, USA. October 2002; 1–10
34. Wang Y, Xiong Y. Effects of Beryllium in Al-Si-Mg-Ti Cast Alloy. Mat. Sci. Eng. A
. 280 (2000), 124–127
35. Jaradeh M, Carlberg T. Effect of Titanium Additions on the Microstructure of DC-Cast Aluminium Alloys. Mat. Sci. Eng. A
. 413–414 (2005), 277-282
36. Krasovskii1 M. O, Lavrenko V. O. Effect of Antimony and Bismuth on the Electrochemical Corrosion of the Cast Aluminium Silicon Alloys in 3% NaCl Solution, Powder Metall. Met. Ceram. 49 (2011), 716–721
37. Stadler F, Antrekowitschn H, Fragner W, Kaufmann H, Pinatel E.R, Uggowitzer P.J. The Effect of Main Alloying Elements on the Physical Properties of Al-Si Foundry Alloys. Mat. Sci. Eng. A
. 560 (2013), 481–491
38. Xiao D.H, Wang J.N, Ding D.Y, Yang H.L. Effect of Rare Earth Ce Addition on the Microstructure and Mechanical Properties of an Al-Cu-Mg-Ag Alloy. J. Alloy. Compd
. 352 (2003), 8488
39. Tao Lu, Ye Pan, Ji-li Wu, Shi-wen Tao, Yu Chen. Effects of La Addition on the Microstructure and Tensile Properties of Al−Si−Cu−Mg Casting Alloys. Int. J. Min. Met. Mater. 22 (4), (2015), 405–410
40. Paiva O. C, Barbosa M. A. Production, Bonding Strength and Electrochemical Behavior of Commercially Pure Ti/Al2O3Brazed Joints. J. Mat. Sci. 32 (1997), 653–659
41. Timsit R. S, Janeway B. J. A Novel Brazing Technique For Aluminum. Weld. J. Res. Suppl. 119s–128s (1994)
42. Andersson R, Holm T, Wiberg S, Astrom A. Furnace Atmospheres, No. 4, Brazing of Metals. Special Edition. Germany: Linde Gas; p. 1–43
43. Ganjeha E, Sarkhoshb H, Bajgholic M.E, Khorsanda H, Ghaffarid M.H. Increasing Ti-6Al-4V Brazed Joint Strength Equal to the Base Metal by Ti and Zr Amorphous Filler Alloys. Mater. Charact. 71 (2012), 31–40
44. Wu X, Li H, Chandel R. S, Seow H. P. Effect of Mechanical Vibration on TLP Brazing With BNi-2 Nickel-Based Filler Metal. J. Mater. Sci. Lett. 18 (1999), 1615–1617
45. Huijie L, Jicai F. Vacuum Brazing TiAl-Based Alloy to 40Cr Steel Using Ag-Cu-Zn Filler Metal. J. Mater. Sci. Lett. 21 (2002), 9–10