采用往复挤压工艺细化Mg-4A1-2Si（AS42）镁合金组织，研究了挤压过程中Mg2Si颗粒的细化效果、破碎特征、分布规律及破碎机制。结果表明：从铸态到挤压8道次态，随挤压道次的增加，颗粒不断细化，均匀度和弥散度逐渐提高；挤压11道次时，颗粒发生粗化；合金在400℃、应变速率0．0lS^-1条件下的压缩峰值应力约为75MPa，大于Mg2Si颗粒的断裂应力（48MPa），挤压使颗粒发生开裂；随挤压道次的增加，位错密度逐渐增大，位错在Mg2Si颗粒处的数量增多，应力集中急剧增大，从而导致颗粒发生破碎。
Microstructure of Mg-4A1-2Si（AS42） magnesium alloy was refined by reciprocating extrusion（RE） process. Refinement effect, breaking feature, regularity of distribution and breaking mechanism of Mg2 Si particles were investigated. The results show that the particles dimension decreased constantly, the eveness and dispersity of Mg2 Si particles increased with increasing the passes of RE from as-cast to 8 passes, however the particles coarsened at RE-11 passes. The peak value of compression stress was about 75 MPa, which was greater than the fracture stress （48 MPa） of Mg2Si particles at 400℃ and strain rate of 0. 01 s^-1, resulting in the particles fractured after RE. The density and amount of the dislocation which assembled around Mg2 Si particles increased with increasing the RE passes, and the stress concentration increased rapidly that led to the particles breaking.
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