A preliminary investigation on microstructure and mechanical properties of dissimilar Al to Cu friction stir welds prepared using silver interlayer

Abstract

Due to its solid-state nature, friction stir welding (FSW) process can be considered a better alternative for dissimilar welding metals. However, like fusion welding techniques, in friction stir welding growth of thick layers of brittle intermetallics -Cu9Al4 and CuAl2 is a significant issue. One solution to this problem is the use of the suitable interlayer material. Use of interlayer material modifies the joint microstructure with the replacement of thick, brittle intermetallics by more ductile intermetallics in a thin layer or particle form. The present study is a preliminary investigation about joining of AA6082-O to pure copper joints with and without silver (Ag) wire interlayer. Friction stir welded joints were characterized regarding optical microscopy, X-Ray Diffraction (XRD) analysis, microhardness measurement, tensile testing and Scanning Electron Microscopy (SEM) based fractography. The Al-Cu weld prepared using silver interlayer was stronger than without it. The higher strength of the weld with silver interlayer is attributed to the formation of a composite type of structure with intercalation of more ductile Ag2Al intermetallics along with dispersion of Ag particles in stir zone.

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.…”

“…Al, and this, along with the Al matrix, forms a composite structure. 12 In an effort to reduce the production of Al-Cu intermetallics, Pandya and Menghani electroplated a thin layer (nearly 15 µm) of pure Zn on the abutting edge of pure Cu sheets before welding. However, at extremely high heat input, intermetallic production was still inevitable.…”

“…An entrapped Al particle was detected within the top region of the Cu side TMAZ, and a slight thinning of the sheet from the top can also be seen due to plunging off the tool. 12 The intermetallics and intercalated layers of Al, Cu, and Age appear in the microstructural image of the FSWed Al/ Ag/Cu stir region (Supplementary Figure 49). The diffused lustrous particles within Al matrix in the stir region, near the weld interface (on the Al side), may be Ag or IMCs of Ag, Al, and Cu (Supplementary Figure 50).…”

“…[1][2][3][4][5][6] It produces lots of brittle intermetallic compounds (IMCs) at the joint interface. [7][8][9][10][11][12] The industries currently replace copper (Cu) with aluminium (Al), either fully or partially due to its high density and costlier nature. The replacement of Cu by Al fully is not possible in most applications so the preparation of their joint is necessary.…”

“…Unlike fusion welding, friction stir welded joints have a microstructure and mechanical properties that are very similar to the base materials (BMs). 1,12,13,19,29,[32][33][34][35][36] Figure 1 shows the main component of the FSW process, a non-consumable rotating tool consisting of a shoulder and pin.…”