TLP Brazing of Aluminum to Steel Using Cu, Ni and Ti Interlayer

Aluminum and steel are the most frequently applied construction materials. They feature well known and complementary material properties and are increasingly used in dissimilar material structures. Hence, it is major importance to provide appropriate joining techniques in order to exploit the full potential of these hybrid structures.

An auspicious approach for the manufacturing of aluminum-steel joints is TLP brazing. Due to moderate process temperatures and controlled diffusion within the joint area, the formation of brittle intermetallics such as Fe₂Al₅ can be prevented to the lowest possible extent.

Within these investigations copper layers has been applied by means of PVD coating on both joining partners, which form a liquid phase with aluminum at 548°C and therefore allow brazements at 580°C. Additionally, diffusion barriers consisting of nickel or titanium were deposited onto the steel in order to decrease the generation of iron aluminides, which initiate cracks due to their immanent brittleness and thus force a premature fracture of the joints. In this regard, nickel as a diffusion barrier shows no significant improvement regarding the joint microstructure compared to copper single layers, whereas joints containing titanium interlayers feature very thin layers of intermetallic precipitates (less than 3 µm) even at high dwell times.