Surface performance of laser-polished low-pressure die casting Al alloy

Low-pressure die-casting (LPDC) aluminum (Al) alloys have been widely utilized in emerging sectors such as new energy vehicles, owing to their benefits in integrated casting and lightweight design. However, the surface quality of LPDC Al alloys often fails to meet direct application requirements. This study applies laser polishing to enhance the surface quality of LPDC A356 alloy. A continuous-wave fiber laser (1060 nm) was used at a fixed scanning speed of 1000 mm/s, with laser power varied from 260 to 340 W to examine its effect on the surface quality. Results indicate that laser polishing significantly reduces surface roughness of the LPDC Al alloy from an initial 6.44 ± 1.70 down to 0.65 ± 0.06 μm, while small deep holes on the as-cast surface are no longer observed after polishing. Microstructural analysis reveals that the surface layer transitions from a structure consisting of α-Al and eutectic Si to α-Al and dispersed Si phases within the grains. The microhardness of the laser-polished layer increases by 89% compared to the substrate, which is consistent with the refined grain structure resulting from the high cooling rate. However, attention is required regarding the corrosion performance of laser-polished surface as it could be influenced by microstructural features such as the nonuniform distribution of fine Si particles in the remelting layer.