Laser Treatment of Al Parts Used for Engines by Surface Alloying with Fe Powder

The combustion engine elements of automobiles are often built from aluminium alloy pistons that slide against cylinders made of cast iron with oil lubrication. For reducing friction and preventing scuffing between pistons and the cylinder, the pistons are sometimes coated. Another possibility is to create a specially treated surface layer, using ceramic particles and laser technology. Using a laser beam makes it possible to locally melt the surface of a piston and incorporate ceramic particles into the molten material. Since ceramic particles are significantly harder than aluminium alloys, this laser-based technology enhances a piston’s resistance to abrasive wear. Furthermore, a laser can be used to create microscopic indentations on the piston surface. This increased roughness helps retain an oil film, which improves lubrication and reduces the risk of dry friction and engine seizure. For this reason, in this work the influence of fibre laser processing parameters on the microstructure and mechanical properties of the aluminium–silicon alloy, especially the crystallographic structure changes, were studied. For alloying, iron powder was used with a size of approximately 60 µm. For investigation of the crystallographic structure, electron diffraction was used on the transmission electron microscope. The hardness measurement was performed using microhardness Vickers at a load of 150 mN and 15 s loading time. Compressive strength, plateau stress, and energy absorption were calculated using a universal testing machine. The highest value of hardness of 192.78 Hv was found when the stress relieving process is set with the following parameters: heating (500 °C); holding time (120 min); and stabilisation temperature (450 °C). Higher heating temperatures and longer holding times have been shown to lead to grain growth, which adversely affects the hardness of the material. Conversely, improvements in the material’s mechanical properties during fibre laser processing were achieved by shortening the holding time and increasing the stabilization temperature. In summary, the results indicate that the heat treatment parameters, such as heating temperature, holding time, and stabilisation temperature, have a significant impact on the mechanical properties of the resulting samples.