不同增强相对挤压态Mg-Zn-Mn-Y合金动态再结晶影响分析

Influence of Secondary Phases on Dynamic Recrystallization Mechanisms in Extruded Mg-Zn-Y Magnesium Alloy

采用Gleeble-3800热模拟试验机进行压缩试验,在温度250～400℃,应变速率0.001～10s-1范围内,研究了变形Mg-Zn-Mn-Y合金中含有不同增强相(I相和W相)对该合金高温流变行为及变形过程中动态再结晶行为的影响。结果表明:只含I相的合金I在较低温度下,表现出明显的加工硬化,峰值应力后发生断裂;在中高温度下,由于发生动态再结晶而表现出明显的流变软化。只含有W相的合金II在中低温度下变形时,峰值应力之前出现加工硬化,随后随动态再结晶的发生而出现软化;在高温下,加工硬化不明显。含有I相合金在变形量较小时(0.1和0.3),其动态再结晶以常规动态再结晶为主,较大变形量时(0.5)的动态再结晶机制为连续动态再结晶。含有W相合金变形量较小时的动态再结晶方式为连续动态再结晶,变形量较大时为旋转动态再结晶。由于含有不同增强相的合金动态再结晶机制不同,含有I相合金在高温下变形可获得均匀细小的再结晶晶粒;而含有W相合金在高温下变形时,晶粒长大。

The combination of low density and moderate strength makes wrought magnesium alloys well suited for the application where weight is of critical importance. In recent years, magnesium alloys containing rare earth Y element have been developed and extensively investigated. Mg-Zn-Y alloys have high specific strength and good creep resistance due to the presence of quasicrystals. The aim of the present study is to investigate DRX behavior and mechanism in extruded Mg-Zn-Y magnesium alloys with different secondary phases （ I- phase and W-phase） using Gleeble-3800 thermo mechanical simulator at the temperature range of 250 -400℃ （in step of 50℃ ） and in the strain range of 0. 001 - 10s 1. The mierostructures of the alloy in the different stages of processing were examined by optical microscopy （OM） and transmission electronic microscopy （TEM）. The conclusions have been drawn from investigation are ： at high temperature of 400℃ and strain rate of ls 1 , when true strain was low （0.1 or 0.3） , DRX mechanism of alloy with I-phase is normal as the ordinary DRX. When the true strain was high （0.5） , the DRX mechanism of alloy with W-phase is CDRX. At temperature of 300℃ and strain rate of 1s -1 , when the true strain was low, DRX mechanism of alloy with W-phase is CDRX, and when true strain was higher, and its DRX mechanism was the RDRX. Because of the DRX mechanisms of alloys with different secondary phases are dif- ferent, the effect of temperature on microstructure of the alloy after deformation were also different. For alloy with I-phase, grain size of DRX was decreased with deformation temperature increased but for alloy with W-phase, DRX grain grows abnormally. The microstructure of alloy with W-phase after deformation could be refined efficiently by increasing the strain.