Mg-4Nd和Mg-4Nd-0．7Zr合金显微组织和力学性能

Microstructures and mechanical properties of extruded Mg-4Nd and Mg-4Nd-0.7Zr alloys

制备了Mg-4Nd和Mg-4Nd-0.7Zr两种合金,并系统研究了它们在各种状态下的组织和性能.研究结果表明:铸态的二元Mg-4Nd合金由α-Mg基体和中间相Mg12Nd组成,少量Zr(0.7%质量百分数)的加入使合金铸态组织得到明显细化,且使Mg12Nd相呈网状连续分布于晶界.合金经热挤压加工后,强度和塑性均得到大幅度改善.由于在合金挤压及热处理过程中,Zr明显提高了再结晶温度并抑制了再结晶后晶粒的长大,因此Zr的加入使Mg-4Nd合金在挤压和时效处理后强度都有不同程度的提高.直接时效(T5)处理工艺能产生形变强化和时效硬化双重作用,使合金呈现良好的综合力学性能.在对合金时效组织的TEM观察中发现了β′和β两种沉淀颗粒,其尺度均在10～100nm之间,它们都对合金产生了沉淀硬化作用.

Two alloys, Mg-4Nd and Mg-4Nd-0. 7Zr, have been prepared in a mild steel crucible. The microstructures and mechanical properties of these two alloys are investigated. The as-cast microstructure of Mg-4Nd alloy consists of α-Mg matrix and an intermetallic compound Mg12Nd. Small amount of Zr addition greatly refines the as-cast microstructure, and results in consecutive distribu- tion of Mg12 Nd along grain boundaries. Hot extrusion causes significant improvement of tensile properties of both alloys. Zr addition to the binary Mg-4Nd alloy raises the recrystallization temperature of the alloy and inhibits the growth of the matrix grains. Therefore, the strengths of extruded and aged specimens of the Mg-4Nd-0. 7Zr alloy are notably higher than that without Zr addition. Direct aging（ T5 treatment） of extruded samples at 225℃ leads to remarkable improvement of tensile properties due to the combined effect of work hardening and age hardening. Transmission electron microscopy （TEM） observations reveal two kinds of precipitates, β＇ and β, from the aged sample. The size of both precipitates are in the range of 10 to 100 nm. The precipitates exhibit significant effect of age hardening on the alloy.