Sometimes when it comes to product design, joining dissimilar metals becomes unavoidable. We don’t need to cover ALL of the possible reasons, but the more common ones are thermal management and mechanical characteristics (strength, corrosion resistance, etc.). Yes, those are very broad topics.
Perhaps it would be best to look at two scenarios:
Case 1: Sensor weldment for corrosion resistance
In this project, the designer has a temperature sensor that is ideally suited for the temperature range and temperature change rate of a fluid (Hydrochloric acid). However, the sensor is not well suited for the medium and would corrode due to its sheath material (304L stainless). In order to achieve a reasonable service life, a sheath of Inconel 625 would be much more appropriate. In this situation, it is not feasible for the sensor manufacturer to make a custom unit out of Inconel. Good news – Inconel 625 and 304L, despite being different alloys, are readily welded together. For a rapid resolution, a sensor sleeve of Inconel 625 can be welded to the 304L sensor, and so long as the 304L portion stays clear of HCl exposure, the life expectancy is excellent.
Case 2: Oven heating element
Specialty heating elements can be made out of a variety of materials, many of them very expensive. For this heating element, the designer needed a section of the unit, which would be exposed to extremely high temperatures, to be made from molybdenum. Making the entire element from “moly” was cost prohibitive, so making the business end from “moly” and the mounting end from 300 series stainless ended up being the solution that fit the bill. This element now has a melting point of almost 4800° F at the working end, and even though the stainless end has a melting point of 2600° F, because of intelligent design and planning it never even gets close. The customer saves money, AND has a highly reliable heating element with no difference in performance over a 100% moly part.
Not all materials can be welded to all other materials, but a surprising number of combinations ARE possible. Stay tuned for some special content in the near future on this very topic. If you have an immediate question about laser welding dissimilar metals – contact us at 860.653-0111!