半固态处理工艺参数对挤压AZ91镁合金微观组织的影响

Effects of Semi-Solid Treatment Process Parameters on Microstructure of Extruded AZ91 Magnesium Alloy

摘要:

研究了半固态等温处理温度和时间对挤压AZ91镁合金微观组织演变的影响。挤压AZ91镁合金的微观组织为流线带状组织，由分布于其间的细小再结晶α-Mg等轴晶组成。在半固态温度区间进行等温处理时，合金内的低熔点相及溶质元素富集区优先开始熔化，然后沿着晶界渗透，形成液相包围固相晶粒的半固态组织。随着等温温度的升高，固相晶粒熔化分离的速度加快。在等温温度为560 ℃时，随着等温时间的延长，液相不断增加，固相晶粒分离并不断趋于圆整。等温处理20 min后，合金达到了固/液平衡状态，Ostwald熟化机制开始明显，晶粒长大成为主要机制。挤压AZ91镁合金较佳的等温处理工艺为等温温度560 ℃，等温时间20~30 min

Abstract:

The effects of semi-solid isothermal heat treatment temperature and holding time on microstructures evolution of extruded AZ91 magnesium alloy were studied. The microstructures of hot extrusion AZ91 magnesium alloy are characterized by streamline structure and small recrystallized α-Mg equiaxed grain. In the semi-solid isothermal treatment, the phase of low melting point begins to melt firstly, then permeates along the grain boundary, and finally the semi-solid structure which is liquid phase surrounded by solid-phase particles is formed. With the increase of isothermal temperature, melt and separation of the solid phases become faster. At the isothermal temperature of 560 oC, with the extension of isothermal holding time, the liquid phases increase obviously, solid phases separate and tend spheroid constantly. After holding for 20 min, the alloy reaches the solid-liquid equilibrium state, Ostwald ripening mechanism begins to be clear, and grains coarsening become the main mechanism. The better semi-solid processing technological parameters of extruded AZ91 alloy are 560 oC and 20~30 min