关键词: LA91镁锂合金, 退火处理, 微观组织, 腐蚀行为

Abstract: Microstructure and corrosion behavior of the extruded LA91 magnesium lithium alloy after annealing at 150-350 ℃ were investigated. The results indicate that the extruded LA91 alloy is a (α+β) biphasic alloy, with the β-Li phase distributing in a filamentous manner in the elongated α-Mg substrate. The electrode potential of β-Li in both the phases is more negative, indicating that the typical corrosion morphology of the extruded alloy is the preferred filamentous corrosion of β-Li along the extrusion direction. As the annealing temperature rises from 200 ℃ to 300 ℃, the β-Li phase and the α-Mg phase undergo equiaxial transformation successively. When annealed at 250 ℃, the original filamentous β-Li phase transforms into fine equiaxed grains, and when the annealing temperature further increases, the β-Li grains start to grow. As the annealing temperature increases, the corrosion resistance of the alloy first increases and then decreases. At an annealing temperature of 250 ℃, the corrosion resistance of the LA91 alloy is optimal, with a corrosion rate of 0.46 mg·cm^-2·d^-1, a self-corrosion current density of 9.73×10^-4A·cm^-2, and a hydrogen evolution rate of 1.01 mL·cm^-2·d^-1. Compared with the extruded alloy, the corrosion resistance is significantly improved. The reason for the improved corrosion resistance is that the β-Li phase is composed of fine equiaxed grains with more grain boundaries, which to some extent hinders the preferred filamentous corrosion of the β-Li phase.

Key words: LA91 magnesium lithium alloy, annealing treatment, microstructure, corrosion behavior