Refined Microstructure and Enhanced Anticorrosion Properties of Mg–4Y–3Nd–0.5Zr Alloy Fabricated by Laser Surface Remelting

Laser surface remelting (LSR) is widely used in the surface modification of magnesium alloys. In the present research, the effects of LSR on the microstructure, phase structure, mechanical properties, and corrosion properties of Mg–4Y–3Nd–0.5Zr alloys are investigated. The experimental results reveal that the LSR treatment considerably refines the grain structure and leads to the formation of metastable eutectic phase (β₁ phase). Compared to as-cast alloys, the grain size after the LSR treatment is refined from 44.8 to 4 μm. The distribution of eutectic phase at grain boundary is changed from discontinuous manner of coarse β phase to continuous manner of fine β₁ phase. Grain refinement is induced by the combined effects of both solute effect of dissolved Zr element and high cooling-rate-induced thermal undercooling intrinsic to LSR. Sharp interface model simulations show that since the movement of solidification front significantly lags the liquidus line, the cooling-rate-induced thermal undercooling is much higher than the critical nucleation undercooling and promotes enormous heterogeneous nucleation. The formation of the network β₁ phase at the intergranular area contributes to the improvement of corrosion resistance, as it acts as a robust barrier and stops corrosion propagation. The present work sheds light on developing high-corrosion-resistance Mg–RE alloys by laser processing techniques such as LSR.

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