Improved strength and interfacial microstructure of dissimilar Al/steel weld via combined addition of Zn and Ni

• The weld strength was improved by 193% through the combined addition of Zn and Ni. • Additional Ni along with Zn further reduced the hardness of the IMC layer. • Fe–Zn phases formed in the IMC layer contributed to the softening of the IMC layer. • Orientation relationships between IMCs were revealed by HRTEM. • Strengthening mechanism of the weld was clarified. The effect of the combined addition of Zn and Ni on the mechanical properties and microstructures of an intermetallic compound (IMC) layer of dissimilar welds of Al alloy 5052 to low-carbon steel was systematically investigated. A maximum weld strength of 120 MPa was achieved with the combined addition of Zn and Ni, which was 193 % higher than that of the weld produced without the addition of Zn or Ni. The addition of Zn resulted in the formation of soft Fe–Zn IMCs in the IMC layer, which reduced the hardness of the IMC layer. Additionally, the combined addition of Zn and Ni promoted the formation of Fe–Zn IMCs, which further softened the IMC layer. Further softening of the IMC layer, reduction in the thickness of the IMC layer, and suppression of the formation of defects in the IMC layer, achieved by the combined addition of Zn and Ni, drastically improved the weld strength.