A component, which may be an automotive chassis structure, includes first and second sub-part main bodies. The first sub-part main body is formed of a first material, and the second sub-part main body is formed of a second material. The first material is a steel alloy, and the second material is aluminum or an aluminum alloy. A transition layer is attached to and contacts the first sub-part main body. The transition layer is formed of a third material, where the third material contains at least a majority of copper. A mixed layer is disposed between the transition layer and the second sub-part main body, and the mixed layer is formed of a mixture of the second material and the third material. A disclosed method includes forming the component by friction stir welding the transition layer to the second sub-part main body.