Microstructural characterisation of alloyed surface layers of an Al-Si alloy laser alloyed with nickel and titanium

Microstructural characterisation of a cast Al-Si alloy was carried out after laser surface alloying with Ni and Ti. When Ni rather than Ti was used for alloying, more severe segregation of the alloying element in the surface alloyed layer was observed. This segregation was attributed to the higher density of Ni. The phases found in the alloyed layer in both cases could be explained by assuming the ternary systems to be equivalent to the corresponding pseudobinary systems, i.e. Al-Si-Ni and Al-Si-Ti ternary systems being equivalent to (AI,Si)-Ni and (AI,Si)-Ti pseudobinary systems, respectively. Segregation of Ni in the alloyed layer resulted in the formation of high Ni-containing phases and low Ni-containing phases in close proximity, whereas the uniform distribution of Ti yielded a single primary phase in the alloyed layer.