【作者】 张新平；

【导师】 袁广银；

【作者基本信息】 上海交通大学 ， 材料学， 2009， 硕士

【摘要】 Mg-Zn系合金是镁合金中最早开发和应用最广的合金系之一,但与铝合金相比,其较低的强度限制了它的广泛应用,为了改善Mg-Zn系合金的性能,本文尝试通过添加Gd、Y元素引入准晶来强化Mg-Zn系合金,Mg -Zn -Gd -(Y)系准晶是一种有独特对称结构、高温下稳定的FK型电子金属间化合物,在Mg-Zn系合金中添加适量的Gd、Y或(Gd+Y)元素可使合金中的主要强化相为准晶相。本文对Mg-Zn-Gd和Mg-Zn-Gd-Y系合金的显微组织及力学性能进行了研究,并就后一种合金的热变形行为进行了详细分析。研究表明:1.当Zn元素含量不变,随着Gd含量增加,Mg -Zn -Gd合金中的第二相依次从准晶相+Mg7Zn3相到准晶相再到准晶相+W相转变,Mg -Zn -Gd -Y系合金在Zn/(Gd+Y)在5～7的范围内,合金中的第二相主要为准晶相,准晶相的成份接近Mg30Zn60(Gd+Y)10;2.准晶相相对Mg7Zn3相、W相而言,在对Mg -Zn -Gd -(Y)合金性能的改善方面具有比较优势,第二相为准晶相的Mg-Zn-Gd-(Y)合金具有较好的综合力学性能,挤压态Mg- 3.5Zn- 0.6Gd(at.%)合金的的抗拉强度、屈服强度和延伸率分别为284Mpa,187 Mpa和13.3%,挤压态Mg -8Zn -2Gd -1Y(wt.%)合金的抗拉强度、屈服强度和延伸率分别为281Mpa,176Mpa和15%。同时,挤压态高准晶含量Mg -Zn -Gd -Y合金比低准晶含量的合金织构弱,但Mg -Zn -Gd -Y合金中形成的织构对合金力学性能的影响较弱,析出相多少和晶粒大小是两种合金力学性能差异的主要原因;3.在热压缩塑性变形过程中,准晶有利于孪晶的生成,可以促进Mg-Zn-Gd-Y合金的动态再结晶,高准晶含量的Mg-Zn-Gd-Y合金具有更好的塑性变形能力。更多还原

【Abstract】 Mg-Zn alloys are one of the well developed and applied Magnesium alloys. However, the use of Mg-Zn alloys has been limited because of their poor mechanical properties in comparison with aluminum alloys.To improve mechanical properties of Mg-Zn alloys, icosahedral quasicrystalline phase (I-phase) is introduced with the addition of Gd、Y. The Mg -Zn -Gd -(Y) I-phase possesses unique fivefold symmetry and a quasiperiodic structure and turns out to be a stable FK-type electron compound. Two phase (I-phase andα-Mg) microstructure of Mg-Zn-Gd-(Y) alloys can be formed with the fixed amount of Gd、Y.The microstructures、mechanical properties of Mg - Zn - Gd alloys and Mg - Zn - Gd - Y alloys、the hot compression deformation behavior of Mg -Zn -Gd -Y alloys have been investigated in this paper.The main conclusions can be summarized as follows:1.With the increasing content of Gd, the second phase transformation was observed as Mg7Zn3+ I-phase→I-phase→I-phase+W-phase,when the Zn/(Gd+Y) of Mg - Zn - Gd - (Y) alloys is fixed between 5～7, the second phase turns out to be I-phase and the I-phase precipitates has a composition of Mg30Zn60(Gd+Y)10 (at.%), belonging to F-type icosahedral structure;2.In comparison with Mg7Zn3 and W-phase, I-phase has better effect on strengthing Mg -Zn -Gd -(Y) alloys, ultimate tensile strength (UTS)、yield strength (YS) and elongation of as-extruded Mg -3.5Zn -0.6Gd(at.%) is 284 Mpa, 187Mpa and 13.3%, that of as-extruded Mg -8Zn -2Gd -1Y(wt.%) is 281Mpa, 176Mpa and 15%.Meanwhile, Mg -Zn -Gd -Y alloy with high content of I-phase exhibits weak basal texture, but the amount of I-phase and the grain size rather than basal texture dominates the mechanical properties of Mg-Zn-Gd-Y alloy;3. I-phase is beneficial to the formation of twins and the dynamic recrystallization of Mg -Zn -Gd -Y alloys can be promoted by I-phase during compression deformation and Mg-Zn-Gd-Y alloy with high content of I-phase shows better plasticity.更多还原