Effects of compound modification and isothermal heat treatment on microstructure and properties of in-situ Mg2Si/Al composites were investigated by compound modification of P and mischmetall and adjusting the insulation temperature and holding time of semi-solid isothermal treatment.The results indicate that after P and mischmetall compound modification

the massive cross-shaped morphology of Mg2 Si primary phase in the composites is transformed into irregular polygons

which are uniformly distributed in Al substrates.The average size of primary phase is decreased from about 83μm before modification to about 17μm.The morphology of Mg2 Si primary phase andα-Al phase is transformed into near-spheric shape after semi-solid isothermal treatment at 570℃for 90 min

and the shape factor of Mg2 Si primary phase reaches up to approximately 0.96 with an average size of about 16μm.Meanwhile

the brinell hardness of the composites reaches a maximum of 106 HB.