Development of High Strength Magnesium Alloys with Long Period Ordered Structure

(1) Mg-TM-RE （TM=Co, Ni, Cu, Zn， RE= Y, Dy, Ho, Er, Dy, Tb， TM）合金形成长周期有序堆积（LPSO）结构。Y、Dy、Ho、Er稀土凝固形成LPSO相，Gd、Tb、Tm稀土在773 K退火析出。(2)在Mg-TM-RE合金中，TM和RE元素形成LPSO结构的标准可以用原子半径、混合焓、晶体结构和在Mg中的固溶度来表示。(3) Mg-TM-RE合金的LPSO结构为10H、18R、14H和24R，其中每隔5、6、7和8周期分别存在两个富集TM和RE的原子层。(4)采用铸锭挤压法制备了室温屈服强度为440 MPa、伸长率为6%、473 K屈服强度为330 MPa的Mg-TM-RE合金。采用切屑挤压固结法制备了室温屈服强度为515 MPa、伸长率为3%、473 K屈服强度为367 MPa的Mg-TM-RE合金。(5) LPSO Mg-TM-RE合金塑性加工的强化机制可能是由于强度较高的LPSO相形成扭结带，基体相（α-M相）通过连续动态再结晶细化晶粒。这种机理不同于一般的加工硬化，是材料强化机理的新概念。

(1) Long period stacking ordered (LPSO) structure was formed in Mg-TM-RE TM=Co, Ni, Cu, Zn, RE= Y, Dy, Ho, Er, Dy, Tb, Tm) alloys. The LPSO phase was formed during solidification for RE of Y, Dy, Ho and Er, and precipitated by annealing at 773 K for RE of Gd, Tb and Tm.(2) In Mg-TM-RE alloys, the criteria of TM and RE elements for forming of LPSO structure can be expressed by atomic radius, mixthing enthalpy, crystal structure and solid solubility in Mg.(3) The LPSO structure recognized in Mg-TM-RE alloys was 10H, 18R, 14H and 24R, in which two atomic layers enriched with TM and RE existed every 5, 6, 7 and 8 periods, respectively, on closed-packed plane.(4) Mg-TM-RE alloy with a yield strength of 440 MPa and an elongation of 6 % at room temperature and a yield strength of 330 MPa at 473 K was developed by extrusion of cast ingot. Moreover, Mg-TM-RE alloy with a yield strength of 515 MPa and an elongation of 3 % at room temperature and a yield strength of 367 MPa at 473 K was developed by extrusion-consolidation of chips.(5) The strengthening mechanism of LPSO Mg-TM-RE alloys through plastic working seems to be due to the formation of kink bands in LPSO phase with relatively high strength, and the grain refinement of matrix phase (α-M phase) by continuous dynamic recrystallization. This mechanism is different from the ordinary work hardening and new concept for strengthening mechanism of materials.