Surface modification of Al–Si alloy by excimer laser pulse processing

• Coarse Si and β phase intermetallic are melted and the constituent elements dispersed into the matrix during re-solidification.
• The solid solubility of the Si at the surface enhanced after the laser treatment.
• The Cellular structure with the size range ∼30–50 nm observed in α-Al after 45 laser pulses.
• Si nano particles in size ∼ 2–15 nm were observed in the intercellular region.
• Surface hardness increased after laser processing.

The laser irradiation on Al-Si alloy sample is carried out by excimer laser in ambient conditions for 30 or 45 pulses. Microstructural investigation of laser treated sample is done by OM, SEM and TEM and the surface hardness is evaluated by Vickers micro indentation. Laser treated, samples suggested the dissolution of coarse primary Si and β-AlFeSi particle in α-Al matrix. The SEM/EDS study shows the enhancement of retained Si in α-Al matrix. The interface analysis of laser treated sample suggested the effected modified depth is ∼6 μm. TEM investigation shows the formation of nanocrystalline Si in size ∼2–15 nm. The cellular structures of size range ∼30–50 nm are observed after 45 pulses. The α-Al cells and Si precipitates sizes were considerably refined at higher number of pulses. The fine Si precipitates are found to be dispersed in the intercellular boundaries. An improvement in surface hardness from ∼1.6 to 1.8 is observed 30 and 45 pulse treatment, respectively. The mechanism involves for improvement in surface properties are non-equilibrium solidification, metastable phase formation and microstructural refinement.