Laser surface alloying of an A356 aluminium alloy using nickel and Ni-Ti-C: A corrosion study

An A356 aluminium alloy was laser surface alloyed with nickel and Ni-Ti-C. A microstructure composed of aluminium–nickel intermetallics in an aluminium silicon matrix was produced when the surfaces were alloyed using nickel. Alloying using Ni-Ti-C resulted in an additional Al-Si-Ti intermetallic and TiC particles that formed by an in situ reaction directly in the melt pool. Corrosion testing was performed to determine any effects on the corrosion resistance due to the alloying process. The testing showed that the alloyed surfaces had reduced corrosion resistance compared to the untreated material. The presence of the intermetallics weakened the protective oxide and resulted in interdenritic corrosion. The surfaces alloyed with a low alloying content of Ni-Ti-C showed better resistance to localised corrosion extending deeply into the material as compared to the surfaces alloyed with nickel. On the other hand, the surfaces alloyed with nickel proved to resist better generalised widespread corrosion.