时效对Mg-Y-Nd合金的影响

研究了Mg-Y-Nd合金时效过程中的硬化软化现象．在时效初期(-473K／2h左右)出现了一次明显的时效硬化峰，之后硬度急剧下降；然后合金的硬度缓慢增加，出现小幅二次硬化现象；523K／600h后，合金出现软化现象微观结构的分析结果表明，初次时效峰是合金中析出了5nm大小的MgY弥散分布沉淀相所致；随后弥散相溶解消失，材料出现软化；在时效过程中β沉淀相的析出、增多和板条状组织的形成导致材料二次硬化．长时间时效后β沉淀相的聚集长大，以及在α／β界面产生纳米晶MgO区导致材料再次软化。

Effect of ageing on Mg-Y-Nd alloys

The effect of ageing on the hardening and softening of Mg-Y-Nd alloys has been studied. An obvious age hardening occurs in alloys aged at 473 K for about 2 h, and then the hardness decreases sharply. A second hardening occurs during the following ageing. But alloys started softening after being aged at 523 K for 600 h. The microstructure investigations by TEM reveal that the first hardening owes to the occurrence of the dispersed precipitate, and the sharp fall of the hardness results from the dissolution of MgY phase. The occurrence and increasing of the precipitate phase and the forming of lathy structure in alloys result in the second hardening. The enlargement of j3 precipitate phase and the formation of nano-size MgO grains at the interface between matrix and (3 phase result in the softening of the Mg-Y-Nd alloy.