Mg-Ni-Zn-Y非晶复合材料的组织与性能研究

发布时间：2018-06-21 16:36

本文选题：组织 + 性能　；参考：《沈阳工业大学》2016年博士论文

【摘要】：镁合金具有低密度、高比强度、易回收利用等优点,在电子、汽车、航空航天等领域得到了广泛的应用。但是一般晶态Mg合金强度相对较低,塑性较高,而非晶态Mg合金强度较高,塑性几乎为零,因此发挥晶态合金的塑性优势和非晶态合金的强度优势,成为本文研究Mg基非晶复合材料的出发点。长周期(LPSO)结构不仅可以作为晶态合金中的增强相,也可作为非晶态合金的增强相,成为人们关注的研究热点。本文采用铜模铸造法制备了LPSO结构增强的Mg-Ni-Zn-Y系列非晶复合材料,通过改变元素含量、样品尺寸,探讨成分、冷却速率对非晶复合材料的组织结构和力学性能的影响,确定非晶复合材料综合力学性能最佳的区域。通过改变热处理温度,研究LPSO结构演化规律。主要结论如下:直径为2 mm的铸态Mg_(77)+xNi_(12)-xZn_5Y_6(x=0,2,4,6,8)系列合金均为非晶复合材料,在非晶基体中分布着黑色针状相。当Ni8%时,针状相细长,主要晶态相为α-Mg相、Mg_(12)YZn长周期相;当Ni8%时,针状相粗大,主要晶态相为α-Mg相、Mg_(12)YZn长周期相和Mg_2Ni相。当Ni=8%时,形成了大小、分布均匀的LPSO相。随着Ni含量的降低,复合材料的塑性先增加再减小,Mg_(81)Ni_8Zn_5Y_6的塑性最好,塑性应变和总应变分别达到20.23%和22.34%。直径为2 mm的Mg_(73)+xNi_(12)Zn_5Y_(10-x)(x=0,2,4,6,8)系列复合材料,当Y8%时,非晶基体中分布着片状α-Mg相和少量针状Mg)*(12)YZn相;当Y8%时,形成粗大针状相,主要晶态相为α-Mg相、Mg_(12)YZn长周期相和Mg_2Ni相。直径为2 mm的Mg_(77+x)Ni_8Zn_5Y_(10-x)(x=2,4,6,8)系列复合材料,当Y4%时,非晶基体中分布着针状相,主要晶态相为α-Mg相和Mg_(12)YZn长周期相;当Y4%时,非晶基体中分布着树枝状α-Mg相、部分Mg_(12)YZn长周期相和Mg2Ni相。随着Y含量的降低,两类复合材料的强度均先降低再升高,Mg_(73)Ni_(12)Zn_5Y_(10)复合材料的断裂强度最高,达到846 MPa。直径为2 mm的Mg_(77)Ni_(12)Zn_(9-x)Y_(2+x)(x=0,2,4,6)系列复合材料,当Zn/Y0.83时,在非晶基体中分布着针状相,主要晶态相为α-Mg相、Mg_(12)YZn长周期相和Mg_2Ni相。随着Zn/Y比的增加,针状相尺寸、含量增加,样品的强度先减小再增加,塑性均较低。直径分别为2 mm、3 mm、5 mm的Mg_(75)Ni_(12)Zn_5Y_8和Mg_(77)Ni_(12)Zn_3Y_8系列复合材料,主要晶态相为α-Mg相、Mg_(12)YZn相和Mg_2Ni相。随着样品直径的增加,针状相的尺寸、含量增加,强度下降,塑性先增加再减小。模拟分析了非晶复合材料中非晶、a-Mg和LPSO等不同相冷却速率与合金凝固组织的对应关系,模拟结果与实验结果相符。Mg-Ni-Zn-Y非晶复合材料的形成机制为:快速冷却过程中,α-Mg相和Mg_(12)YZn相作为领先相先析出,Mg_2Ni相可伴随Mg_(12)YZn相的析出同时形核,随温度降低晶态相长大;当温度降低到Tg以下时,剩余液相形成非晶,最终形成以非晶为基体,晶态相分布其上的非晶复合材料。铸态、473 K热处理5 h、773 K热处理5 h后Mg_(81)Ni_8Zn_5Y_6非晶复合材料的LPSO相分别为14H、18R、6H结构。LPSO相的稳定顺序为14H18R6H,Ni含量适当提高,有利于形成更稳定的LPSO结构。Mg-Ni-Zn-Y非晶复合材料中的针状LPSO相具有空间网络结构。随着Ni含量的降低,LPSO相数量增加,尺寸变细。随着Y含量的降低,LPSO相数量减少、尺寸变大。随着Zn/Y的增加,LPSO相数量减少,尺寸变大。Mg-Ni-Zn-Y非晶复合材料的强度和塑性与LPSO相的形态和体积分数有关,LPSO相尺寸适当、分布均匀、体积分数较高时有利于复合材料塑性的提高。随着LPSO相体积分数的增加,复合材料的塑性明显增加,强度变化不大。力学性能最佳的成分范围为一个三角形,其三个顶点的合金成分分别为Mg_(8)3Ni_6Zn_5Y_6、Mg_(79)Ni_8Zn_5Y_8和Mg_(79.68)Ni_8Zn_5Y_(7.32)。获得了Mg-Ni-Zn-Y非晶复合材料的断裂机制和断口特征。断裂机制表现为非晶剪切带滑移受到长周期相阻碍,长周期相变形诱发新的剪切带产生,当这个过程贯穿整个样品滑移面时,样品便发生断裂。Mg-Ni-Zn-Y非晶复合材料的断口可分为晶态相特征区、撕裂特征区、脉状纹特征区,其中晶态相特征区可表现为针状相或光滑的α-Mg相滑移区,撕裂特征区与锯齿状不连续应力-应变曲线相对应,脉状纹特征区是绝热剪切所造成的非晶基体熔化聚集的结果,断口出现裂纹可抑制这一区域的出现。
[Abstract]:Magnesium alloy has many advantages, such as low density, high specific strength, easy recovery, and so on. It has been widely used in the fields of electronics, automobile, aerospace and other fields. But the strength of the general crystalline Mg alloy is relatively low, the plasticity is higher, and the strength of the amorphous Mg alloy is higher and the plasticity is almost zero, so the plastic advantage of the crystalline alloy and the strength of the amorphous alloy are strong. The degree advantage is the starting point for the study of Mg Based Amorphous Composites. The long period (LPSO) structure not only can be used as an enhanced phase in crystalline alloy, but also as an enhanced phase of amorphous alloy. This paper has prepared a Mg-Ni-Zn-Y series amorphous composite with enhanced LPSO structure by copper mold casting. The influence of the element content, sample size, composition and cooling rate on the structure and mechanical properties of amorphous composites was investigated, and the best comprehensive mechanical properties of amorphous composites were determined. By changing the heat treatment temperature, the evolution law of LPSO structure was studied. The main conclusions are as follows: the cast Mg_ (77) +xNi_ (12) -xZn_5 with diameter of 2 mm Y_6 (x=0,2,4,6,8) alloys are Amorphous Composites with black needle like phase in the amorphous matrix. When Ni8%, the needle like phase is long, the main crystalline phase is alpha -Mg phase, Mg_ (12) YZn long period phase; when Ni8%, the acicular phase is large, the main crystalline phase is alpha -Mg phase, Mg_ (12) YZn long period phase and Mg_2Ni phase. When Ni=8%, the size, distribution are formed. With the decrease of the content of Ni, the plasticity of the composite increases first and then decreases, the plasticity of Mg_ (81) Ni_8Zn_5Y_6 is the best, the plastic strain and the total strain reach 20.23% and the 22.34%. diameter is 2 mm Mg_ (73) +xNi_ (12) Zn_5Y_ (10-x) (x=0,2,4,6,8) series. When Y8%, the amorphous matrix is distributed in the amorphous matrix and a small amount. Needle like Mg) * (12) YZn phase; when Y8%, a large needle like phase is formed, the main crystalline phase is alpha -Mg phase, Mg_ (12) YZn long period phase and Mg_2Ni phase. The diameter of Mg_ (77+x) Ni_8Zn_5Y_ (10-x) series is 2 mm. The matrix is distributed in the dendrimer like alpha -Mg phase, part Mg_ (12) YZn long period phase and Mg2Ni phase. With the decrease of Y content, the strength of the two kinds of composite materials decreases first and then increases. The fracture strength of Mg_ (73) Ni_ (12) Zn_5Y_ (10) composite is the highest, and the 846 MPa. diameter is 2 mm Mg_ (12) series composite material. At n/Y0.83, the needle like phase is distributed in the amorphous matrix, the main crystalline phase is alpha -Mg phase, Mg_ (12) YZn long period phase and Mg_2Ni phase. With the increase of Zn/Y ratio, the size and content of the needle phase increase, the strength of the sample decreases first and then increases, the plasticity is lower. The diameter is 2 mm, 3 mm, 5 mm Mg_ (75) Ni_ (12) Zn_5Y_8 and 77 (12). The main crystalline phase is the alpha -Mg phase, the Mg_ (12) YZn phase and the Mg_2Ni phase. With the increase of the sample diameter, the size, the content, the strength and the plasticity of the acicular phase increase and then decrease. The corresponding relationship between the cooling rate of amorphous, a-Mg and LPSO in Amorphous Composites and the solidification structure of the alloy is simulated and analyzed, and the simulation results and experiments are carried out. The result shows that the formation mechanism of.Mg-Ni-Zn-Y Amorphous Composites is that in the rapid cooling process, the alpha -Mg phase and the Mg_ (12) YZn phase precipitate as the leading phase, and the Mg_2Ni phase can accompany the precipitation of Mg_ (12) YZn phase at the same time, and the crystal phase grows with the temperature. When the temperature is below Tg, the remaining liquid phase forms amorphous, and finally forms the amorphous base. The crystalline phase is distributed on the amorphous composite. As cast, 473 K heat treatment 5 h, 773 K heat treatment 5 h, LPSO phase of Mg_ (81) Ni_8Zn_5Y_6 composite material is 14H, 18R, 6H structure.LPSO phase is 14H18R6H, the content is improved, which is beneficial to the formation of a more stable amorphous composite material in the amorphous composite material SO phase has space network structure. With the decrease of Ni content, the number of LPSO phase increases and the size becomes thinner. With the decrease of Y content, the number of LPSO phase decreases and the size becomes larger. With the increase of Zn/Y, the number of LPSO phase decreases and the size of.Mg-Ni-Zn-Y amorphous composite is related to the morphology and volume fraction of LPSO phase, and the LPSO phase size is suitable. When the distribution is uniform and the volume fraction is higher, the plasticity of the composite is improved. With the increase of the volume fraction of the LPSO phase, the plasticity of the composite increases obviously and the strength changes little. The optimum composition range is a triangle, and the alloy components at its three vertices are Mg_ (8) 3Ni_6Zn_5Y_6, Mg_ (79) Ni_8Zn_5Y_8 and Mg_ (7), respectively. 9.68) Ni_8Zn_5Y_ (7.32). The fracture mechanism and fracture characteristics of Mg-Ni-Zn-Y amorphous composites are obtained. The fracture mechanism shows that the slip of the amorphous shear band is hindered by the long periodic phase and the new shear band is induced by the long period phase deformation. When this process runs through the whole sample slip surface, the sample will break the.Mg-Ni-Zn-Y amorphous composite. The fracture can be divided into crystal phase characteristic area, tearing characteristic area and pulse pattern feature area, in which the crystalline phase characteristic area can be acicular phase or smooth alpha -Mg phase slip zone. The tearing characteristic area is corresponding to the sawtooth discontinuous stress strain curve, and the characteristic area of the pulse pattern is the result of the melting and aggregation of the amorphous matrix caused by the adiabatic shearing. The occurrence of this area can be suppressed by the occurrence of cracks.
【学位授予单位】：沈阳工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG139.8

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