Mg2Si/Mg-5Zn-2.5Er composites were fabricated by repeated plastic working （RPW） via solid state reaction and hot extrusion. Number of RPW was 100

200

300 and 400

respectively. Effects of RPW times on microstructure and mechanical properties of the composites were investigated by XRD （X-ray diffraction）

SEM （scanning electron microscope） and OM （optical microscope）. The results show that with increasing in RPW times

size of Mg2Si phase is gradually decreased with more uniform distribution. With 200 times RPW

the composites exhibit desirable comprehensive mechanical properties

and average grain size in the composites reaches 1.8 μm

decreased by 81.6% compared with that of samples without RPW

which is attributed to the grain refinement caused by repeated plastic deformation and grain growth caused by dynamic recrystallization during solid state reaction and hot extrusion. In addition

tensile strength reaches 394MPa

increased by 25.4% compared with that of ones without RPW

and elongation makes 5.5%. The strengthening mechanism of the prepared composites is characterized by grain refinement.