Laser Remelting Technology-ShangHai RunQia Electronics Technology Co.,Ltd.

Laser Remelting Technology

Laser remelting is also called laser melting quenching. It is a surface modification technology that uses a laser beam to heat and melt the workpiece surface to a certain depth. The molten layer then solidifies through self-cooling, so as to obtain a refined and homogeneous microstructure as well as desired surface properties.

The principle of laser remelting is basically consistent with that of laser amorphization. However, both the laser energy density and scanning speed adopted in laser remelting are much lower than those in laser amorphization.

Different from laser alloying, laser remelting generally does not add any alloying elements during surface melting. The remelted layer forms a natural metallurgical bonding with the material substrate. In the laser remelting process, impurities and gases can be eliminated. Meanwhile, the microstructure obtained by rapid cooling and recrystallization possesses high hardness, wear resistance and corrosion resistance, and the depth of its surface molten layer is far greater than that of laser amorphization.Microstructure of Laser Remelted LayerThe microstructure of the laser remelted layer depends on the base metal. For alloys capable of solid-state phase transformation such as iron-based and titanium-based alloys, the remelted microstructure in the laser-affected zone consists of three layers: the surface molten zone, the subsurface solid-state phase transformation zone, and the inner transition zone.

For alloys unable to undergo solid-state phase transformation (such as nickel-based alloys and austenitic stainless steel), the remelted microstructure only contains a single molten zone. The microstructure of the molten zone is similar to that of the laser alloyed zone, generally presenting ultra-fine eutectic structure or fine dendritic structure.

Laser grain refinement is especially applicable to cast alloys. Taking cast aluminum alloy AA390 containing coarse primary silicon particles (about 60 μm) with an Al–Si eutectic matrix as an example, after laser remelting with a 3.5 kW laser beam, a spot diameter of 4 mm and a scanning speed of 8.47 mm/s, fine silicon particles of 1–4 μm are uniformly distributed in the matrix, and the hardness is significantly improved.

For pearlitic ductile iron treated by laser remelting, a dendritic microstructure can be obtained under ultra-short irradiation time (corresponding solidification rate > 5×10⁴ K/s), while a lamellar ledeburite microstructure forms with longer irradiation time (solidification rate < 10⁴ K/s).

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