Effects of different adding methods of Cu nanoparticle on the properties of Al/Cu joints with ultrasonic assistance

A mixture of 65% SAC0307 and 35% Zn was employed as the solder , with nano-Cu particles being incorporated through three distinct methodologies to investigate their effects on Al/Cu joint performance under ultrasonic assistance. The results indicate that the addition of nano-Cu particles in different ways has varying impacts on the performance of Al/Cu joints. With the addition of nano-Cu particles, the Al/Cu joints exhibit good forming quality, with no cracks, voids, or other obvious defects observed. At the Al-side interface, no reaction occurs between Al and Cu, and only an Al-Zn solid solution is formed. At the Cu-side interface, a complete and continuous Cu₅Zn₈ layer is formed. Under the ratio of (65-x) % SAC0307 + 35 % Zn + x % Cu, as the content of Cu particles increases and the content of SAC0307 particles decreases, the strength of the Al/Cu joint first increases and then decreases. When the Cu content is 10 %, the shear strength of the joint reaches a maximum of 26.09 MPa, which only increases by 6.8 % compared to the shear strength of the joint without nano-Cu particles (24.43 MPa), indicating an insignificant improvement. Under the ratio of 65 % SAC0307 + (35-x) % Zn + x % Cu, increasing the nano-Cu content while reducing the Zn particle content decreases the shear strength of the Al/Cu joint. When the Cu content reaches 15 %, the shear strength of the joint drops to a minimum of 12.42 MPa, representing a 49.16 % reduction compared to the shear strength of the joint without nano-Cu (24.43 MPa) . By maintaining the optimal ratio of SAC0307 particles and Zn particles, increasing the nano-Cu content achieves the best strengthening effect. When the nano-Cu content increases to 10 %, the shear strength of the joint reaches a maximum of 27.65 MPa, which is a 13.2 % increase compared to the shear strength of the joint without nano-Cu.