Laser remelting of AlSi10Mg(-Ni) alloy surfaces: influence of Ni content and cooling rate on the microstructure

Abstract

AlSi10Mg alloys are widely employed in a variety of industries, including aerospace, automotive, and microelectronics. This is because of its low density, acceptable mechanical properties, acceptable corrosion resistance, and inexpensive application cost. Advantageous fluidity, a short solidification period, and minimal volumetric contraction are beneficial characteristics under processing such alloys. Despite being used as commercial alloys, the mechanical properties of the AlSi10Mg alloys still need to be improved. In line with this, the current focus of Al-based alloy development is mostly on modifying commercially available alloys. Under such context, Ni was used as an alloying element in this study to generate the Al3Ni intermetallics, distinguished by its improved mechanical strength. Furthermore, the thermal stability of the Al3Ni may be a benefit, particularly for high-temperature applications. The present study aims to investigate the solidification under low and high cooling rates of four alloys: AlSi10Mg, AlSi10Mg-1Ni, AlSi10Mg-2Ni, and AlSi10Mg-3Ni (wt.%). Samples were obtained by directional solidification (DS) and laser surface remelting (LSR) processes. The cooling rates were calculated for the DS samples and with extrapolation for LSR samples as well as with the use of a model from the literature. After testing several laser conditions, the results also include an examination of microstructural and hardness changes in the treated and untreated zones. The produced gradient of microstructures is fully characterized as well as used to evaluate cooling rates inside the laser molten pools. For energy densities of 400 J/mm2 and 100 J/mm2, the mean dendritic spacings, λ, of the three Ni-containing alloys at the laser molten pool yielded estimated cooling rates of approximately 1.5 × 104 °C/s and 4.7 × 104 °C/s, respectively. A model explaining the reversion of λ across the molten pool will be outlined.