M92Si reinforced Mg-Al based composite with high amount o/silicon was prepared by permanent mould casting, and then extruded by reciprocating extrusion （RE） after the composite was processed by homogenization heat treatment. The effect of RE processing on the morphology and size of M92Si and the mechanical properties of the com- posite were investigated, to develop new ways to refine the M928i phase and improve its shape. The result showed that RE was very useful in refining the M92Si phase. The more the RE processing passes, the better the refining effect would be. Moreover, the uniform distribution of M928i phases would be more in the composite. After the composite was processed by RE for 12 passes, most M92Si phases were equiaxed, with granular diameter below 20 μm, and distributed uniformly in the matrix of the composite. The mechanical properties of the composite could be increased prominently by RE processing, and were much higher than that in the as-cast state. As the temperature rises, the tensile strength is reduced. For the composite RE processed for 12 passes, the tensile strength, yield strength, and elongation are 325.9 MPa, 211.4 MPa, and 3.3% at room temperature, whereas, 288.2 MPa, ,207.7 MPa, and 7.8%, respectively, at 150℃. In comparison with the properties at room temperature, the tensile strength and yield strength are high and only decrease by 11.6% and 1.8% at 150℃. The M928i reinforced Mg-Al based composite possesses good heat resistance at 150℃. The excellent resistance to effect of heat is attributed to the high melting tempera- ture and good thermal stability of fine Mg2Si phases, which are distributed uniformly in the composite, and effectively hinder the grain boundary gliding and dislocation movement.
Mg68Zn28Y4 alloys with stable icosahedral quasicrystals(Zn60Mg30Y10)were prepared by cast method.By simulating the environment of ocean,the alloy was eroded in 3.5%(mass fraction)NaCl for 2,4 and 30 h.The microstructures of the samples and eroded alloys were analyzed by OM and SEM.The compositions and the quasiperiodic structures were identified respectively by EDS and TEM.And the corrosion potential and corrosion current density before and after immersion were measured by potentiodynamic polarization measurements in 3.5%NaCl.The results show that I-phases grow in the mode of conglomeration, piling and transfixion.The Mg7Zn3 matrix andα(Mg)solid solution are eroded badly,while W-phase is eroded partially.At the same time,the I-phases exhibit excellent corrosion resistance property.The resistance to corrosion of Mg68Zn28Y4 alloy is improved by increasing exposed I-phases.With adding element Y to Mg68Zn32 alloy,the corrosion current is decreased by one order of magnitude. And after the immersion of as-cast Mg68Zn28Y4 alloy for 30 h,the corrosion current density is reduced by two orders of magnitude compared with that of uneroded Mg68Zn32 alloy.
