Enhancing metallurgical and mechanical properties of friction stir butt welded joints of Al-Cu via cold sprayed Ni interlayer

Intermetallic compounds (IMCs) formation is a key factor which limits the strength of dissimilar friction stir welded joints. To suppress the formation of brittle phases at the interface, a cold sprayed Ni interlayer was introduced to the copper surface before applying friction stir butt welding of Al alloy to Cu. The results indicated that when no Ni interlayer was added, the IMCs formed at the interface were Al2Cu and Al4Cu9, each of which had a thickness of similar to 0.6 mu m. When a Ni interlayer was used, a single Al3Ni2 layer was generated with a thickness of similar to 200 nm. With the addition of Ni interlayer, the average tensile strength of the joint was increased from 152 MPa to 190 MPa. The joint ductility was also significantly improved from similar to 5.5% to similar to 10.5%. The improvement of ductility is a result of a fracture path change from the Al/Cu interface, to through the Al alloy stir zone instead.