In some specific markets, for example battery and medical device manufacturing, there is an increasing need to weld dissimilar materials. The trend is also found across general manufacturing, as a way to maximize part performance as individual component material can be selected for optimized operational properties rather than compromising functional properties of a lesser material to ensure weldability.
It is important to assess the metallurgy of the weld when considering two materials to weld, as many desirable dissimilar material combinations create intermetallic regions that can cause brittleness. Brittle welds are weaker than either of the two materials in the weld. Therefore, it is critical to conduct fitness for purpose testing. When assessing if a material combination is viable for a specific application, it is important to minimize heat input and laser time on the part.
Table under provides general guidelines on dissimilar material selection:
|Material 1||Material 2||Comments|
|Aluminium||Cold rolled steel||Can be bonded - brittle intermetallics are created at the interface. Fitness for purpose testing essential.|
|Aluminium||Copper||Can be bonded - brittle intermetallics are created at the interface. Fitness for purpose testing essential.|
|Stainless steel||Nitinol||Can be bonded - brittle intermetallics are created at the interface. Fitness for purpose testing essential.|
|Stainless steel||Inconel||OK with certain alloys (304 with 600/700), need to watch for cracking. When welding, offset into the steel to promote high Cr/N ratio in weld metal|
|Titanium||Aluminium||OK with certain aluminium alloys (1xxx & Ti-6Al-4V)|
Welding different alloys within the same family of metal should also be considered as dissimilar welding – and approached with the same caution. The common families are stainless steel and aluminum.
Welding stainless steels within the 3XX series is generally successful, but it is worth noting that 303 and 316 are problematic materials. Because 303 is a free-machining steel containing sulfur, it is poor for welding, causing cracking and porosity. However, pairing it with 304L can produce a weldable combination – providing the mixing ratio favors the 304L. This can be further mitigated by using a CW rather than pulsed laser, as the CW laser reduces the thermal cycling of the parts.
For the 316, the final chromium/nickel ratio of the weld material must be greater than 1.7 to ensure reliable welds devoid of cracking. Again, the use of a CW laser helps in welding of 316.
Welding the 4XX series can be problematic, due to its carbon content and the other alloying elements for ferrite stabilization. However, welding is generally helped by welding to 3XX steels.
Welding different aluminum alloys can be considered dissimilar material welding, due to the large differences among these alloys. The important factor is ensuring that the percentage of the alloy elements in the weld does not promote cracking. With electronic packages, seam welding is routinely completed between 6061 and 4047 aluminum alloys, because the level of Silicon (Si) in the 4047 moves the overall alloy percentage into the safe 7-8 percent range.
Joining two different aluminum alloys that are each weldable must be undertaken with an understanding of the final alloy composition. For example, when two weldable alloys such as 3003 and 5052 are welded together, they are prone to cracking.