简介概要

往复挤压Mg-4Al-2Si镁合金的晶粒细化

来源期刊:中国有色金属学报2010年第4期

论文作者:宋佩维

文章页码:606 - 612

关键词:镁合金;Mg-4Al-2Si合金;往复挤压;动态再结晶;晶粒细化

Key words:Mg alloy; Mg-4Al-2Si alloy; reciprocating extrusion; dynamic recrystallization; grain refinement

摘    要:研究往复挤压Mg-4Al-2Si (AS42)合金的显微组织和晶粒细化机制。结果表明:挤压过程中发生受位错攀移控制的动态再结晶,随挤压道次的增加,合金的晶粒尺寸迅速减小;对合金挤压8道次后,得到晶粒细小、均匀分布的等轴晶组织,晶粒尺寸由铸态的45 μm减小至1.5 μm,此时,合金组织的细化趋于稳定,达到细化极限;晶粒细化机制是在往复挤压过程中通过累积动态再结晶,使再结晶得以彻底完成;增加位错密度和加剧晶界畸变使再结晶形核数目增多;大量挤压破碎、均匀分布的Mg2Si第二相颗粒成为再结晶形核核心,从而使晶粒得以细化;往复挤压11道次时,由于挤压温度过高,导致晶粒发生异常长大,最大尺寸约为10 μm。本试验条件下晶粒发生异常长大的温度阀值约为400 ℃。

Abstract: The microstructures and grain refinement mechanisms of Mg-4Al-2Si (AS42) alloy by reciprocating extrusion (RE) were investigated. The results show that the dynamic recrystallization controlled by dislocation climbing occurs during the RE process. The grain size of the alloy decreases rapidly with increasing RE pass. The grain size of the as-cast alloy deceases from 45 μm to 1.5 μm after RE 8 passes, here the grain refinement is up to the limit. The mechanisms of grain refinement are that, during RE, the recrystallization is completed thoroughly by accumulative dynamic recrystallization, the nucleation numbers of recrystallization increases with increasing dislocation density and grain boundaries distortion severity, and the massive broken Mg2Si particles become nucleating center of dynamic recrystallization, thus, resulting in the grain refinement. The grain begins to coarse up to 10 μm due to high temperature after RE 11 passes. Under the experimental conditions, the blow-threshold temperature of the grain coarse is about 400 ℃.

基金信息:陕西理工学院专项科研基金资助项目



详情信息展示

可见,界面能愈大、晶粒尺寸愈小,则晶粒长大的驱动力愈大,则长大的倾向愈大。2) 晶粒长大主要表现为晶界的移动,实质上就是原子在晶界附近的扩散。而原子的扩散受加热温度、保温时间、第二相颗粒的性质、大小和数量等因素的影响。由于随挤压道次的增加,合金挤压温度逐步提高,当挤压11道次时,挤压温度已经从2道次时的375 ℃提高到11道次时的400 ℃,此时,晶界扩散和晶界迁移能力增强,且挤压时间较长,导致晶粒发生异常长   大[17];同时,原来细小、弥散分布的Mg2Si相颗粒也发生粗化,其颗粒总数相应减少,则基体晶粒发生再结晶形核位置数目也就相应减少,且粗化的第二相对晶界的钉扎作用减弱,这也导致晶粒发生快速长大;3) 往复挤压产生的应变更进一步加速原子的扩散,促使晶粒长大。

总而言之,挤压温度过高是晶粒长大的主要原因。可以推断,在本研究的挤压条件下,晶粒发生异常长大的温度阀值约为400 ℃。

3  结论

1) 往复挤压可显著细化AS42合金的显微组织。挤压过程中α-Mg基体组织发生了受位错攀移控制的动态再结晶,随挤压道次的增加,动态再结晶速度加快,晶粒尺寸迅速减小。挤压8道次时,得到晶粒细小、均匀分布的等轴晶组织,晶粒尺寸由铸态的45 ?m减小至1.5 ?m。此时,合金组织的细化趋于稳定,达到了细化极限。

2) 通过累积动态再结晶,使再结晶得以彻底完成;增加晶内缺陷(如增加位错密度和加剧晶界畸变)使再结晶形核数目增多;提供大量均匀分布的Mg2Si第二相颗粒,使其成为再结晶形核核心。通过上述几方面的作用使晶粒得到细化。

3) 往复挤压11道次时,由于挤压温度过高,导致晶粒发生粗化,最大尺寸达10 ?m;本试验条件下,晶粒发生异常长大的温度阀值约为400 ℃。

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(编辑  龙怀中)


                                 

基金项目:陕西理工学院专项科研基金资助项目(SLGQD0746)

收稿日期:2009-04-27;修订日期:2009-08-21

通信作者:宋佩维,副教授,博士;电话:13892633273:E-mail:spwsyh@163.com

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