The effects of extrusion temperature, extrusion speed and extrusion passes on microstructure of the as-cast Mg-5Sn-1.5Al-1Zn-1Si magnesium alloy were studied. The results indicate that the uniformity of alloy microstructure increases firstly, and then reduces with the increase of extrusion temperature. When temperature is lower, the dynamic recrystallization is slow and the grain sizes are uneven; when the temperature is higher, the dynamic recrystallization process is accelerating and grains are coarse. With the increase of extrusion speed, the grain size decreases firstly and then increases, a slower or faster extrusion speed will cause inhomogeneous distribution of the microstructure. When the extrusion speed is slower, the secondary recrystallization processes occur easily, while the faster extrusion speed causes insufficiency of recrystallization process. With the increase of extrusion passes, the microstructure uniformity improves gradually and the grain size decreases firstly and then increases. After reciprocating extrusion (REX) for more than 7 passes, the refining effect becomes weaken and large grains appear in the microstructure again, and the dislocation configuration transforms from dislocation walls to dislocation cells.%研究挤压温度、挤压速度及道次对铸态Mg-5Sn-1.5Al-1Zn-1Si合金显微组织的影响。结果表明：合金显微组织的均匀性随着挤压温度的升高表现出先提高后降低的趋势。当温度较低时，动态再结晶过程缓慢，晶粒尺寸不均匀；当温度较高时，动态再结晶过程速度加快，晶粒较粗大。晶粒尺寸随着挤压速度的增加表现出先减小后增大的趋势，速度较小或较大均会造成合金显微组织的不均匀。当挤压速度较小时，容易出现二次再结晶过程；当挤压速度较大时，再结晶过程不充分。随着挤压道次的增加，合金显微组织的均匀性逐渐提高，晶粒尺寸表现出先减小后增大的趋势。往复挤压超过7道次后，晶粒细化效果减弱，合金显微组织中重新出现大尺寸的晶粒，位错组态由位错墙向位错胞转化。
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