| Mg-Sn-Zn(Al)系镁合金的组织与力学性能 | |
| Alternative Title | Microstructures and Mechanical Properties of Mg-Sn-Zn(Al) Magnesium Alloys |
| 周吉学 | |
| Subtype | 博士 |
| Thesis Advisor | 杨院生 |
| 2006-12-26 | |
| Degree Grantor | 中国科学院金属研究所 |
| Place of Conferral | 金属研究所 |
| Degree Discipline | 材料加工工程 |
| Keyword | 镁合金 Mg-sn-zn合金 Mg-sn-al合金 组织 力学性能 热处理 挤压 |
| Abstract | 镁合金是目前广泛应用的工程结构材料中密度最小、比强度最高的金属材料，在航空工业、汽车工业和电子通讯工业中具有巨大的应用潜力。但是，镁合金由于绝对强度低、变形能力弱以及耐腐蚀性能差等原因，至今未得到大规模应用。镁合金的成分设计，作为镁合金发展的基础工艺，可以为镁合金的后续处理及加工提供良好的基础，促进镁合金的快速发展。因此设计具有良好的综合性能的新型镁合金非常有必要。本文重点研究Mg-Sn-Zn(Al)系镁合金在铸态、热处理以及变形状态下的组织、力学性能和断裂行为，为研制新型高性能镁合金提供实验和理论依据。 首先明确了Mg-Sn二元系中Mg-7Sn合金的凝固过程及凝固组织。Mg-7Sn合金凝固组织由α-Mg基体、(Mg + Mg2Sn)共晶与离异共晶相Mg2Sn以及二次析出相Mg2Sn组成，Sn在枝晶间明显偏析。在本文实验条件下，Mg-7Sn合金的凝固序列为：L L1 + 初生相(-Mg) -Mg + 离异共晶(Mg2Sn) + 共晶(Mg + Mg2Sn) -Mg +离异共晶(Mg2Sn) + 共晶(Mg + Mg2Sn) + 二次析出相(Mg2Sn)。 实验考察了Mg-xSn-5Zn系列合金的凝固组织和力学性能。其中，Mg-5Sn-5Zn(TZ55)合金凝固组织由基体α-Mg、网格状(Mg + MgZn)共晶组织与离异共晶相Mg2Sn以及二次析出Mg2Sn相组成。离异共晶Mg2Sn主要分布在晶界处，其中一部分与网格状(Mg + MgZn)共晶连接生长，另外一部分单独分布。二次析出Mg2Sn相依附于MgZn相或者离异共晶相Mg2Sn析出，或者在晶粒内部析出。TZ55铸态合金的室温抗拉强度、屈服强度以及延伸率分别为236.5MPa、90.5MPa与12.7%；150℃抗拉强度、屈服强度以及延伸率分别为141.3MPa、75.8MPa与39.2%，表现出优异的塑性。 考察了Mg-Sn-Al系列合金的凝固组织和力学性能。其中，Mg-4Sn-5Al(TA45)合金凝固组织由枝晶α-Mg、层片状共晶与离异共晶(Mg+β-Mg17Al12)、离异共晶相Mg2Sn以及二次析出Mg2Sn相组成。离异共晶Mg2Sn主要分布在晶界处，其中一部分与层片状(Mg+β-Mg17Al12)共晶或者离异共晶Mg17Al12连接生长，另外一部分单独分布。二次析出Mg2Sn相依附于离异共晶Mg17Al12相或者离异共晶相Mg2Sn析出，或者在晶粒内部析出。TA45合金性能最优，室温抗拉强度、屈服强度与延伸率分别为242.5MPa、102.4MPa与14.4%，150℃抗拉强度、屈服强度以及延伸率分别为167.0MPa、87.0MPa与22.0%。 分别对TZ55合金与TA45合金进行了不同条件下的固溶与时效处理。固溶处理后两种铸态合金组织中的MgZn相或者-Mg17Al12相以及大部分Mg2Sn相被固溶到基体中，组织中只残余少量的不规则的Mg2Sn相，同时合金元素分布均匀，微观偏析消除。固溶处理显著提高了合金的抗拉强度与延伸率，与铸态相比，TZ55合金的室温抗拉强度与延伸率提高到270.1MPa与20.0%，TA45合金的室温抗拉强度与延伸率提高到260.1MPa与17.0%，但屈服强度有所降低。经过时效处理，TZ55合金的室温抗拉强度与屈服强度分别进一步提高到291.6MPa与183.3MPa，合金的延伸率则降低到10.5%；TA45合金室温抗拉强度与屈服强度分别进一步提高到282.6MPa与163.7MPa，延伸率降低到8.2%。 分别对TZ55合金与TA45合金进行了热挤压以及挤压后时效处理。合金挤压变形后，组织中形成了挤压纤维织构，合金晶粒明显细化，力学性能显著提高。TZ55与TA45合金的抗拉强度、屈服强度、延伸率分别达到了294.2MPa、188.2MPa、20.0%与283.9MPa、187.7MPa、20.0%。经时效处理后，晶粒内部及晶界上析出大量细小弥散析出相，晶界存在的细小和均匀分布的弥散析出相阻碍晶界滑移而使合金性能提高。时效后TZ55与TA45合金的抗拉强度、屈服强度、延伸率分别达到了329.3MPa、294.7MPa、8.8%与288.9MPa、195.8MPa、16.0%。 Sr可以明显细化TZ55与TA45，以及AZ91D、AZ80、AS31等镁合金晶粒，Sr的细化晶粒作用主要是由于Sr在凝固过程中在固-液界面前沿富集，从而阻碍初生相生长导致的。添加Sr后由于镁合金凝固组织的改善导致TZ55、TA45等镁合金的力学性能提高。 |
| Other Abstract | Magnesium alloys are particularly attractive for the aerospace and automotive industries due to their low densities, high strength to weight ratio and good machinability. However, magnesium alloys have not been widely used as a main structural material because of their low tensile strength, low deformation ability and bad corrosion resistance. Therefore, it is necessary to design a new type of magnesium alloy which exhibits good properties. For developing a new magnesium alloy, the composition design is the precondition and foundation for the subsequent processing to improve properties. The present paper is to study the microstructures and mechanical properties of a new series of Mg-Sn-Zn(Al) magnesium alloys as well as the strengthening mechanism for the alloys. The microstructure of as-cast Mg-7Sn alloy consists of -Mg primary, Mg+Mg2Sn eutectic, divorced eutectic Mg2Sn and secondary precipitation Mg2Sn. The solidification sequence of Mg-7Sn alloy is as follows: L L1 + -Mg -Mg + Divorced eutectic (Mg2Sn) + Eutectic (Mg+Mg2Sn) -Mg + Divorced eutectic (Mg2Sn) + Eutectic (Mg+Mg2Sn) + Secondary precipitation (Mg2Sn). It is observed there exists dendritic segregation of Sn in this alloy. The microstructures and tensile properties of as-cast Mg-xSn-5Zn alloys are investigated. The solidified microstructure of Mg-5Sn-5Zn (TZ55) alloy is composed of -Mg primary, Mg+MgZn eutectic, divorced eutectic Mg2Sn and secondary precipitation Mg2Sn. Some divorced eutectic Mg2Sn phase adheres to the eutectic MgZn phase, and some distributes alone. Secondary precipitation Mg2Sn appears within the -Mg grains or adhering to the eutectic MgZn and divorced Mg2Sn. The tensile strength, yield strength and the elongation of the TZ55 alloy are 236.5MPa, 90.5MPa, 12.7% at room temperature and 141.3MPa, 75.8MPa, 39.2% at 150℃, respectively, which indicates that TZ55 alloy has high ductility. The microstructures and tensile properties of as-cast Mg-Sn-Al alloys are investigated as well. The solidified microstructure of Mg-4Sn-5Al (TA45) alloy consists of -Mg primary, Mg+β-Mg17Al12 eutectic, divorced eutectic Mg2Sn and secondary precipitation Mg2Sn. Some eutectic Mg2Sn adheres to Mg+β-Mg17Al12 eutectic or divorced eutectic β-Mg17Al12, and some distributes alone. Secondary precipitation Mg2Sn appears within grains or adheres to β-Mg17Al12 and divorced Mg2Sn. The tensile strength, yield strength and the elongation of TA45 alloy at room temperature and 150℃ are 242.5MPa, 102.4MPa, 14.4% and 167.0MPa, 87.0MPa, 22.0%, respectively. The solution treatment and solution-aging treatment are carried out for TZ55 and TA45 alloys. After solution treatment, all the MgZn (or -Mg17Al12 ) particles and the majority of Mg2Sn particles are dissolved into the matrix, and the solute distribution within the matrix is homogeneous. The tensile strength and the elongation of TZ55 and TA45 alloys are improved obviously to 270.1MPa and 20.0%, respectively, for TZ55, and 260.1MPa and 17.0%, respectively, for TA45 alloy. However, the yield strength of the two alloys is decreased. After aging, the yield strength and the tensile strength of TZ55 alloy increase to 183.3MPa and 291.6MPa, respectively, while the elongation decreases to 10.5%. The yield strength and the tensile strength of the aged TA45 alloy increase to 163.7MPa and 282.6MPa, respectively, while the elongation decreases to 8.2%. The microstructures and tensile properties of as-extruded TZ55 and TA45 alloys as well as the two aged alloys are investigated. The results show that the tensile properties of TZ55 and TA45 alloys are significantly improved due to the extrusion texture and fine microstructures. The tensile strength, yield strength and the elongation of the extruded TZ55 alloy reach to 294.2MPa, 188.2MPa and 20.0%, respectively, and that of the extruded TA45 alloy are 283.9MPa, 187.7MPa and 20.0%, respectively. After aging, many fine precipitates distributes within the matrix and along the grain boundaries in the extruded TZ55 and TA45 alloys and these fine precipitates can strengthen the alloys by blocking dislocation slipping. The tensile strength, yield strength and the elongation of the extruded and aged TZ55 alloy reach to 329.3MPa, 294.7MPa, 8.8%, respectively, and 288.9MPa, 195.8MPa, 16.0%, respectively, for TA45 alloy. The addition of Sr can refine the grains of TZ55, TA45, as well as AZ91D, AZ80, and AS31 alloys, obviously. The grain refinement mechanism is attributed to the enrichment of Sr at the solidification interface front which restricts the growth of α-Mg. The tensile properties of these alloys are improved by Sr addition. |
| Pages | 133 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.imr.ac.cn/handle/321006/17243 |
| Collection | 中国科学院金属研究所 |
| Recommended Citation GB/T 7714 | 周吉学. Mg-Sn-Zn(Al)系镁合金的组织与力学性能[D]. 金属研究所. 中国科学院金属研究所,2006. |
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