Method for manufacturing clad material

1. A method for manufacturing a clad material, comprising:

performing a Ni plating treatment on a Cu material made of Cu or a Cu-based alloy to make a Ni-plated Cu material in which the entire surface of the Cu material is covered with a Ni plating layer;

softening the Ni-plated Cu material by performing a softening heat treatment as a first heat treatment on the Ni-plated Cu material at a holding temperature of 650° C. or higher and 850° C. or lower before rolling;

bonding an Al material made of Al or an Al-based alloy and the softened Ni-plated Cu material on which the softening heat treatment has been performed to each other by rolling to make the clad material after performing the softening heat treatment; and

performing diffusion annealing as a secondary heat treatment on the clad material at an annealing holding temperature of 500° C. or higher and 600° C. or lower which is lower than the holding temperature after rolling.

2. The method for manufacturing the clad material according to claim 1 , wherein the Al material and the Ni-plated Cu material on which the softening heat treatment has been performed are bonded to each other by the rolling at a rolling reduction of 40% or more and 90% or less.

3. The method for manufacturing the clad material according to claim 2 , wherein the Al material and the Ni-plated Cu material on which the softening heat treatment has been performed are bonded to each other by the rolling at a rolling reduction of 60% or more and 80% or less.

4. The method for manufacturing the clad material according to claim 1 , wherein the holding temperature is 700° C. or higher and 850° C. or lower.

5. The method for manufacturing the clad material according to claim 1 , wherein the softening heat treatment is performed on the Ni-plated Cu material at the holding temperature for 0.5 minutes or more and 5 minutes or less.

6. The method for manufacturing the clad material according to claim 1 , wherein

each of the Al material and the Ni-plated Cu material is plate-shaped, having a side end face perpendicular to a thickness direction, and

the side end face of the plate-shaped Al material perpendicular to the thickness direction and the side end face of the plate-shaped and heat-treated Ni-plated Cu material perpendicular to the thickness direction are made adjacent to each other and bonded to each other by the rolling.

7. The method for manufacturing the clad material according to claim 6 , wherein the clad material is a bus bar for a lithium-ion secondary battery.

8. The method for manufacturing the clad material according to claim 1 , wherein

each of the Al material and the Ni-plated Cu material is plate-shaped, and

a surface of the plate-shaped Al material in a thickness direction and a surface of the plate-shaped and heat-treated Ni-plated Cu material in the thickness direction are made adjacent to each other and bonded to each other by the rolling.

9. The method for manufacturing the clad material according to claim 8 , wherein the clad material is a terminal for a lithium-ion secondary battery.