8 September 2014

Laser welding dissimilar materials

The growing desire to join dissimilar metals is offering significant challenges for many welding methods. In principle, laser welding can be applied to any material(s) – similar or dissimilar - which can be successfully joined by other processes. The weldability of dissimilar metals depends on many different factors. The physical properties of the resultant weld are influenced by the amount of energy coupled in and the heat transfer. Most important for sound weld properties is that there be good solubility of the various elements of the metals and alloys in the finished weld joint.

When joining dissimilar materials, there can be certain advantages in using laser welding even though brittle intermetallic compounds may tend to form. Since the weld is narrow, the volume of intermetallic may be reduced to acceptable limits. Also, it may be possible to offset the beam favouring one material or the other, thus allowing some control over composition of the resulting alloy.

Within the past weeks, extensive development has been performed at Prima Power Laserdyne for welding a range of materials used in electronics applications. Materials and material combinations which were part of this development included aluminum alloys, pure copper, aluminum to copper, stainless steel to copper, copper to nickel, aluminum to nickel, and nickel coated steels. It should be noted that most of these materials pose particular challenges to be joined together. Laser and processing parameters were optimised to produce welds which exhibited sound mechanical and electrical properties.

One application for dissimilar metal welding that helped Laserdyne define the materials for this experimental work is the construction of Li-ion batteries for electric vehicles. Automobile manufacturers throughout the world are focusing on electric vehicles. The battery technology currently in use is lithium ion because this leads to batteries that are smaller and lighter than current automotive power batteries (generally, Nickel Metal Hydride). The Li-ion technology can provide power equivalent to current technology at a smaller size and lighter weight, or more power at an equivalent size and weight.

The batteries used in the electric vehicle batteries (EVB) are composed of many components (i.e. interconnect cover, bus bar, control and cover plate electronics and lithium ion prismatic cell) and these are constructed from a combination of different materials. The good news is that we have demonstrated successful welding of a significant number of similar and dissimilar metal alloys.

Image: Overlap weld of 0.75 mm, 50 µm, and 0.75 mm thick copper alloy C110 (99.9% pure copper)

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