退火处理对挤压态LA91 镁锂合金组织与耐蚀性的影响

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 ^{- 4} A·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.