Effect of the Composition of Absorbing Coatings on the Structure and Properties of a Cast Aluminum Alloy Subjected to Surface Laser Heat Treatment

摘要

The microstructure, microhardness, surface roughness and chemical composition of the AK7ch cast aluminum alloy are studied after surface laser heat treatment, which is performed using new dextrin-based absorbing coatings of different compositions, namely, composition 1 (the water solution of dextrin + Na2O(SiO2)n) and composition 2 (the water solution of dextrin + ZnO). It has been established that, for the best surface quality (Ra = 1.03–3.60 μm) and the greatest depth (0.7–1.16 mm) of the molten zone to be achieved, it is expedient that laser heat treatment of the AK7ch alloy should be carried out using an absorbing coating of composition 1, both with a CO2 laser (radiation wavelength λ = 10.6 μm) and a fiber laser (λ = 1.070 μm). At that, laser heat treatment decreases the sizes of α-Al dendritic cells from 50–190 μm to 5.0–11.5 μm and the sizes of silicon crystals from 5–30 μm to 0.5–2.0 μm, whereas microhardness increases by a factor of 1.11–1.22 from that of the as-cast alloy (90 HV0.025). An even distribution of alloying elements in the molten zone is also ensured.