An Investigation of the Effect of Intermetallic Compounds on the Mechanical and Electrical Properties of Friction Stir Welded Al and Cu Busbar for Battery Pack Applications

Abstract

Aluminium and copper (Al-Cu) busbar is widely used as a core component in Lithium-Ion (Li-ion) batteries. The Al-Cu busbar is challenging to fabricate with the traditional welding processes because of its high thermal conductivity. In the present study, the Al-Cu busbar is fabricated using the friction stir welding method. The effect of temperature and vibration generated during the welding process on the formation of intermetallic compounds (IMCs) is studied by using the effective formation model and found that Al2Cu is the first to form at the interface. The IMC formation at the joint interface had both detrimental (Al-rich IMC) and beneficial (Cu-rich IMC) effects. The presence of detrimental IMCs affects the joint strength of about 36 % as compared to the sample with the highest tensile load. The surface electrical conductivity is measured by using a Gaussian profile method and found in the range of 0.94 – 5.37 μ Ω·mm. The welded samples with the presence of Al2Cu3 and Al4Cu9 IMC at the interface are found to have higher electrical conductivity. Interestingly, the sample with a higher tensile load had observed higher electrical conductivity due to the formation of Cu-rich IMC, i.e., Al4Cu9.

A review on recent development in aluminium-copper friction stir welding

“…When Al-Cu is welded without interlayer either through butt configuration or lap configuration, the IMCs formed are AlCu, 2,7,11,16,20,22,26 Al 2 Cu, 2,7,11,16,[20][21][22]26,110,111,113,114 Al 2 Cu 3 , 7,11,20,22,112 Al 3 Cu 4 , 20,22 and Al 4 Cu 9 . 7,11,12,16,20,22,26,109,[111][112][113][114] Mechanical properties of FSWed Al-Cu joints Sahu et al investigated the hardness of dissimilar friction stir welded Al-Cu joints. They reported that the bottom layer's hardness was higher than the upper and middle layers, as well as the thickness of the weld, due to the faster cooling rate and the presence of different IMCs.…”

“…The higher the welding speed, the more vibration was generated, resulting in the formation of larger Cu-rich intermetallic Al 4 Cu 9 , which improved tensile strength and electrical characteristics. 112 Muhammad and Wu produced the joints of Al-Cu by placing Al in RS and AS and named as I joint and II joint, respectively. They compared the electrical conductivity with UTS of different type joints formed by FSW and UVaFSW as shown in Supplementary Figure 39, and their given results are as follows 124 :…”

“…When Al-Cu is welded without interlayer either through butt configuration or lap configuration, the IMCs formed are AlCu, 2,7,11,16,20,22,26 Anormall2Cu, 2,7,11,16,20-22,26,110,111,113,114 Anormall2Cnormalu3 , 7,11,20,22,112 Anormall3Cnormalu4 , 20,22 and Anormall4Cnormalu9. 7,11,12,16,20,22,26,109,111-114…”

“…The higher the welding speed, the more vibration was generated, resulting in the formation of larger Cu-rich intermetallic Anormall4Cnormalu9, which improved tensile strength and electrical characteristics. 112…”