| Magnesium alloys are the most promising light materials, for which they have low density, high specific strength, high specific stiffness, great shock absorption and good electromagnetic shielding effects. At present, magnesium alloys are applied to aeronautics and astronautics, automotive power train, computer, communication, consumerelectronics fields. Conventional casted magnesium alloys can merely meet those requirements with low strength and not too high emperature situations, for its crystal structure determines its poor mechanical performances. One rare earth magnesium alloy was developed, but due to its high cost, this alloy could only used on those aeronautics, astronautics and military condidions that they don’t care for the expenses. The advantages of the magnesium alloys can’t be fully employed in civil industries, which forces us to exploit one kind of low-cost heat-resistant magnesium alloy.Nonmetallic element silicon is of great amount in the nature and of low cost. Mg2 Si generates when silicon reacts with magnesium. Mg2 Si phase has a high melting point(1085 celcius), high hardness and high elastic modulus. Mg2 Siphase exists as two shapes, one as polygonal blocks and one as Chinese-characterlike. We can control the melting procedure to reduce the amount of polygonal block Mg2 Si to produce as much as Chinese-character-like Mg2 Si phase. Mg2 Si phase can be refined by equal channel angular pressing(ECAP) process. Crushed Mg2 Si becomes small particles and will reinforce the magnesium alloy.We employ conventional casting to melt ZAM84-xSi(x=0, 1, 2, 3, 4) alloys, then we apply ECAP to refine the alloys and discuss which alloy treatment process is the best.In ZAM84-xSi alloys, Mg2 Si shape varies from the content of silicon. Mg2 Si appears as small Chinese-character-like, there appears some filamentous Mg2 Si when the Si content is 1wt%. Mg2 Si shows as well-disspersed Chinesecharacter-like with 2wt% Si. With silicon content of 3wt%, half of the Mg2 Si appears as polyganol block and half Chinese-character-like. When the silicon content increases to 4%, most of the Mg2 Si exists as polyganol block. Polyganol block are hardly to be refined. After 1 pass ECAP, the grains of ZAM84、ZAM84-1Si、ZAM84-2Si were refined to some extent. The ?-Mg matrix of the ZAM84-3Si、ZAM84-4Si were refined, while the Mg2 Si wasn’t notably refined because of the large amount of polyganol block. For as cast ZAM84-xSi alloys, ZAM84-2Si has the highest UTS(208MPa), and the highest yield strength(79MPa). As cast ZAM84-2Si has the best room temperature mechanical properties. After 1 pass ECAP, ZAM84-1Si has the highest UTS(273MPa), ZAM84-2Si has the highest yield strength(128MPa), ZAM84-2Si has the maximum elongation(7.48%). ZAM84-2Si has the best mechanical properties.The creep stress exponent of as cast ZAM84-4Si alloy is 2.32 at 200 ℃. The creep deformation is dominated by grain boundary sliding mechanism accompanied with viscous dislocation motion mechanism. The creep stress exponent of as cast ZAM84-4Si alloy is 3.56 at 225 ℃. The creep deformation is dominated by the combination of dislocation climb and viscous dislocation motion mechanism. The creep stress exponent of ZAM84-4Si alloy ECAPed for 1 pass is 2.13 at 200 ℃. The creep deformation is dominated by combination of grain boundary sliding and viscous dislocation motion mechanism. The creep stress exponent of ZAM84-4Si alloy ECAPed for 1 pass is 3.85 at 225 ℃. The creep deformation is dominated by combination of dislocation climb and viscous dislocation motion mechanism. The creep stress exponent of ZAM84-4Si alloy ECAPed for 1 pass is 5.10 at 250 ℃. The creep deformation is dominated by combination of dislocation climb mechanism. The steady creep stress exponent increases with the elevating of the temperature. Creep activation energy increases with increasing temperature. ZAM84-xSi magnesium alloys ECAPed for 1 pass ZAM84-1Si has the longest creep life, and its elongation after creep rupture is the maximum. |
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