When joining dissimilar metals, there can be certain advantages coming from laser welding simply because of the relatively low, concentrated heat input and accompanying rapid cooling rates in the weld. These contribute to limited heat affected zone and fine structure with lower tendency for formation of brittle intermetallic compounds that may occur depending upon the materials being joined.
The wonderful characteristic of the Cu-Ni alloy system is that the copper and nickel atoms are completely soluble within each other both in the liquid and solid phases – see the figure below. This makes welding these two materials easy from the materials standpoint – of course, fixturing, and developing the correct laser parameters are still key to a successful application.
|Phase diagrams, such as that for the Cu-Ni alloy system pictured here, can be useful in predicting the welding behavior of dissimilar metal combinations. However, it is important to recognize that phase diagrams assume slow cooling, whereas laser welding typically results in much faster cooling which can modify the as-welded structure.|
It is also important – more important than for welding steels – that the material in the area around the weld joint be thoroughly pre-cleaned. Cleaning must remove grease, oil, inks and similar contaminants. Also, if the joint edges are cleaned by abrasives, it is important that they not have been used for cleaning other materials so as to avoid introducing other metals into the weld.
|Lap weld of 1mm Cu to 1.5mm pure nickel produced using a CW (continuous wave) fiber laser. The picture on the right shows the weld fusion zone within the thickness of the copper. Note the mixing of the nickel (gray color) from the lower portion of the joint into the copper.|