BACKGROUND

Joining of dissimilar metals in the automotive industry is typically accomplished through the use of adhesives or mechanical fasteners. However, mechanical fasteners require added weight, cost, parts, and assembly time. Adhesives require specialized equipment, increased takt time, and a separate thermal cycle to cure the adhesive to full strength. Changing to a different joining process often requires new infrastructure in factory assembly lines, costing additional capital investment, line re-design, and personnel training.

Fusion welding is also often used to join two metal pieces. However, a barrier to fusion welding dissimilar metal materials is the formation of intermetallic compounds (IMCs), as well as solidification or “hot” cracking induced by different solidification temperature ranges of different molten compounds in the weld pool and galvanic corrosion. IMCs are often brittle and can result in weak joint strength, while hot cracking creates fractures in the weld pool as the weld cools, and galvanic corrosion can result in joint failure as one of more of the base metals erode due to exposure to an electrolytic solution while in electrical contact with each other.

One method of averting the problems of formation of IMCs and solidification cracking is through the addition of a filler material that dilutes the weld pool, preferentially forms acceptable compounds, or provides physical separation of the incompatible elements in the weld pool. Filler material is typically preplaced in a joint prior to welding or added to the weld pool during welding as in Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW) and some instances of Gas Tungsten Arc Welding (GTAW).

Galvanic corrosion can be prevented by accommodating the change in electronegativity between the base metals by incrementally using intermediate materials that have electronegativity between that of the two base metals. Additionally, by placing additional filler material between the base metals, physical separation makes simultaneous contact by an electrolytic solution less likely, thereby preventing galvanic corrosion.

BRIEF DESCRIPTION

According to one aspect, a welded assembly comprises a first component including a first metal material, a second component including a second metal material that is different from the first metal material, a transition material arranged between and contacting the first component and the second component. The transition material comprises one or more of a high entropy alloy, a pure element, and an alloy that is not a high entropy alloy. The assembly also includes an ultrasonic weld joining the transition material to the first component, and a fusion weld joining the first component to the second component. The fusion weld contacts the first component, the second component, and the transition material. The amount or level of one or more of galvanic corrosion, intermetallic compounds, and solidification cracking in the fusion weld is less than if the first component was fusion welded directly to the second component without having the transition material arranged between and contacting the first component and the second component.

According to another aspect, a method of making a welded assembly comprises providing a transition material ultrasonically welded to a first component, arranging the transition material between the first component and a second component such that the transition material contacts the second component, and joining the first component to the second component by forming a fusion weld between the first component and the second component. The first component comprises a first metal material, the second component comprises a second metal material that is different from the first metal material, and the transition material comprises one or more of a high entropy alloy, a pure element, and an alloy that is not a high entropy alloy. The fusion weld contacts the first component, the second component, and the transition material. Upon joining, the amount or level of one or more of galvanic corrosion, the formation of intermetallic compounds, and solidification cracking in the fusion weld is reduced as compared to if the first component was joined directly to the second component without having the transition material arranged between the first component and the second component.

