锻后热处理对镁合金组织和性能的影响
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摘要
镁合金具有重量轻、比强度高、阻尼减震性好等优点,广泛应用于工业领域,而AZ系列变形镁合金因其高的变形工艺性能而成为最主要工业应用变形镁合金。
作为“挤锻复合成型工艺研究”专利技术研究的一部分,本文采用时效过程硬度检测、金相观察、X-衍射(XRD)、拉伸实验、扫描电镜(SEM)断口分析等方法,重点研究了挤压AZ81、AZ61、AZ61E材料经模压变形及模压后时效热处理过程中的材料时效热行为、显微组织演变、力学性能变化及断裂失效机制,为挤锻复合成形工艺生产高强韧镁合金结构件奠定组织性能调控基础。
研究结果表明:
①等温模锻能显著提高合金的综合力学性能。在本实验通过对AZ81采取在60%变形量下,在400℃变形温度,5.6mm/s变形速度条件下对试样进行等温模锻成形,锻后试样强度进一步提升,合金抗拉强度达到337.6MPa,屈服强度达到227.9MPa,延伸率达到15.83%,硬度(HRE)74.8。
②等温模锻态材料AZ81在400℃×0.5h固溶+200℃×20h人工时效后,合金达到硬化峰值(HRE)86.7,综合力学性能最好,合金抗拉强度达到355.8MPa,屈服强度达到255.28MPa,延伸率达到10.3%。对人工时效后力学性能的分析发现,抗拉强度和屈服强度先是升高,然后随着保温时间延长再降低,延伸率则是随着保温时间延长一直减小,但是在低温150℃降低的幅度最小,随温度的升高降低的幅度越来越大。合金内β-Mg17Al12相在晶内和晶界弥散析出。试样的室温拉伸断裂,由锻压时的韧性解理断裂转化为热处理后的韧脆性混合断裂。
③在AZ61基础上添加稀土制备成的等温模锻态材料AZ61E在400℃×0.5h固溶+200℃×15h人工时效(T6)处理,合金达到硬化峰值(HRE)75.8,综合力学性能最好,合金抗拉强度达到304.78MPa,屈服强度达到258.73MPa,延伸率达到9.12%。
④AZ61中Ce稀土的加入,由于对Al的“钉扎”使得Al4Ce相的扩散速度大大降低,α-Mg中Al的浓度减小,使AZ61镁合金的硬度峰值出现滞后,且较AZ61力学性能有所降低,但是其延伸率的下降幅度比AZ61小。
Magnesium alloys have found wide variety of applications in different industries, due to its low density, high specific strength& stiffness and good damping capacity. Among the commercial magnesium alloys, AZ series wrought Mg alloys have become one of the most important wrought Mg alloys in the field of industries because of its good processing property.
As a part of the“Net-shape forming via close die pressing of extruded perform”patent. The microstructure and properties of AZ61, AZ61E and AZ81 alloy in as forged and aging states were investigated with hardness test, optical microscopy, X-ray diffraction (XRD), tensile test and scanning electron microscopy (SEM) analysis. Laid the foundation of using extrusion-forging forming process to produce high toughness magnesium alloy
The main conclusions are as follows:
①The obtained results indicate that during the isothermal forging, At 60% compression ratio, 400℃deformation temperature, 5.6mm/s deformation velocity isothermal forging in this study, the strength of the sample AZ81 alloy further enhanced. The tensile strength, yield strength, elongation and hardness of the specimens after extruded-forging compound deformation reach 337.6MPa, 227.9MPa, 15.83% and 74.8.
②Artificial aging after isothermal forging obtained the hardness peak (HRE) 86.7, the best mechanical properties of tensile strength of 355.8MPa, the yield strength of 255.28MPa, extension rate of 10.3% at 400℃×0.5 solution +200℃×20h artificial aging condition,. analysed the mechanical properties found that tensile strength and yield strength increased firstly, then as time prolonging, the elongation is reduced, and at low temperature 150℃the smallest decrease, with the temperature elevated elongation reduced increasingly. The forged specimens, Alloy phase of theβ-Mg17Al12 precipitated in the grain and grain boundaries. The room temperature tensile fractures show tough in as-forged condition while becomes a mixed ductile-brittle fracture in as- heat treatment condition.
③AZ61 magnesium alloy with RE contents after isothermal forging, the best mechanical properties of tensile strength of 304.78MPa, the yield strength of 258.73 MPa, extension rate of 9.12% at 400℃×0.5 solution +200℃×15h artificial aging condition.
④AZ61 magnesium alloy with Ce content, due to its pinning to the Al element, makes the diffusion speed of Al4Ce reduced greatly, the concentration of Al inα-Mg decreased. All those lead the hardness peek of AZ61 lag behind, mechnical properties also reduced, but the rate of elogation decline is lower than AZ61.
作为“挤锻复合成型工艺研究”专利技术研究的一部分,本文采用时效过程硬度检测、金相观察、X-衍射(XRD)、拉伸实验、扫描电镜(SEM)断口分析等方法,重点研究了挤压AZ81、AZ61、AZ61E材料经模压变形及模压后时效热处理过程中的材料时效热行为、显微组织演变、力学性能变化及断裂失效机制,为挤锻复合成形工艺生产高强韧镁合金结构件奠定组织性能调控基础。
研究结果表明:
①等温模锻能显著提高合金的综合力学性能。在本实验通过对AZ81采取在60%变形量下,在400℃变形温度,5.6mm/s变形速度条件下对试样进行等温模锻成形,锻后试样强度进一步提升,合金抗拉强度达到337.6MPa,屈服强度达到227.9MPa,延伸率达到15.83%,硬度(HRE)74.8。
②等温模锻态材料AZ81在400℃×0.5h固溶+200℃×20h人工时效后,合金达到硬化峰值(HRE)86.7,综合力学性能最好,合金抗拉强度达到355.8MPa,屈服强度达到255.28MPa,延伸率达到10.3%。对人工时效后力学性能的分析发现,抗拉强度和屈服强度先是升高,然后随着保温时间延长再降低,延伸率则是随着保温时间延长一直减小,但是在低温150℃降低的幅度最小,随温度的升高降低的幅度越来越大。合金内β-Mg17Al12相在晶内和晶界弥散析出。试样的室温拉伸断裂,由锻压时的韧性解理断裂转化为热处理后的韧脆性混合断裂。
③在AZ61基础上添加稀土制备成的等温模锻态材料AZ61E在400℃×0.5h固溶+200℃×15h人工时效(T6)处理,合金达到硬化峰值(HRE)75.8,综合力学性能最好,合金抗拉强度达到304.78MPa,屈服强度达到258.73MPa,延伸率达到9.12%。
④AZ61中Ce稀土的加入,由于对Al的“钉扎”使得Al4Ce相的扩散速度大大降低,α-Mg中Al的浓度减小,使AZ61镁合金的硬度峰值出现滞后,且较AZ61力学性能有所降低,但是其延伸率的下降幅度比AZ61小。
Magnesium alloys have found wide variety of applications in different industries, due to its low density, high specific strength& stiffness and good damping capacity. Among the commercial magnesium alloys, AZ series wrought Mg alloys have become one of the most important wrought Mg alloys in the field of industries because of its good processing property.
As a part of the“Net-shape forming via close die pressing of extruded perform”patent. The microstructure and properties of AZ61, AZ61E and AZ81 alloy in as forged and aging states were investigated with hardness test, optical microscopy, X-ray diffraction (XRD), tensile test and scanning electron microscopy (SEM) analysis. Laid the foundation of using extrusion-forging forming process to produce high toughness magnesium alloy
The main conclusions are as follows:
①The obtained results indicate that during the isothermal forging, At 60% compression ratio, 400℃deformation temperature, 5.6mm/s deformation velocity isothermal forging in this study, the strength of the sample AZ81 alloy further enhanced. The tensile strength, yield strength, elongation and hardness of the specimens after extruded-forging compound deformation reach 337.6MPa, 227.9MPa, 15.83% and 74.8.
②Artificial aging after isothermal forging obtained the hardness peak (HRE) 86.7, the best mechanical properties of tensile strength of 355.8MPa, the yield strength of 255.28MPa, extension rate of 10.3% at 400℃×0.5 solution +200℃×20h artificial aging condition,. analysed the mechanical properties found that tensile strength and yield strength increased firstly, then as time prolonging, the elongation is reduced, and at low temperature 150℃the smallest decrease, with the temperature elevated elongation reduced increasingly. The forged specimens, Alloy phase of theβ-Mg17Al12 precipitated in the grain and grain boundaries. The room temperature tensile fractures show tough in as-forged condition while becomes a mixed ductile-brittle fracture in as- heat treatment condition.
③AZ61 magnesium alloy with RE contents after isothermal forging, the best mechanical properties of tensile strength of 304.78MPa, the yield strength of 258.73 MPa, extension rate of 9.12% at 400℃×0.5 solution +200℃×15h artificial aging condition.
④AZ61 magnesium alloy with Ce content, due to its pinning to the Al element, makes the diffusion speed of Al4Ce reduced greatly, the concentration of Al inα-Mg decreased. All those lead the hardness peek of AZ61 lag behind, mechnical properties also reduced, but the rate of elogation decline is lower than AZ61.
引文
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[2] Mordike B L, Ebert T. Magnesium Properties-applications-potential [J]. Materials Science and Engineering A, 2001, 30(2):37-45.
[3] Friedrich H, S chumann .S Research for a new age of magnesium in the automotive industry. Journal of Materials Processing Technology, 2001, 11(7):276-281.
[4]周海涛,马春江,曾小勤等.变形镁合金材料的研究进展[J].材料导报,2003,17(11):16-18.
[5]余琨,黎文献,王日初等.变形镁合金的研究、开发及应用[J].中国有色金属学报, 2003,13(2):277-288.
[6]余琨,黎文献,李松瑞.变形镁合金材料的研究进展[J].轻合金加工技术,2001,29(7):6-11.
[7]陈振华,夏伟军,严红革等.变形镁合金[M].北京:化学工业出版社,2004,1-371.
[8]徐日瑶.镁冶金学[M].北京:冶金工业出版社,1981.
[9]陈振华等编著.镁合金[M].北京:化学工业出版社,2004.
[10] ABussiba A.Ben Artzy A.Ashtechmen S.et, al.Grain refinement of AZ31 and ZK60 Mg [J]. Matereals Sience and Engineering, 2003, (275):274.
[11] M. T. Perez-Prado,O. A. Ruano. Texture Evolution During Annealing of Magnesium AZ31 Alloy [J]. Scripta Materialia, 2002, (46):149-155.
[12]夏翠芹,刘平,任凤章等.细晶变形镁合金的研究进展[J].材料导报,2006(9):89-92.
[13] Yu Yoshida, Hideaki Yamada, Shigeharu Kmado. Microstructures and tensile proerties of ECAE processed Mg-Al-Zn alloys [J]. J. of Japan Institute of Light Metals, 2001, 51(10): 556-562.
[14] H.K. Kim, W.J. Kim. Microstructure Instability and Strength of and AZ31 Mg Alloy after Severe Plastic Deformation [J]. Matereals Sience and Engineering, 2004, (385):308.
[15]靳丽.等通道角挤压变形镁合金微观组织与力学性能研究.上海交通大学博士学位论文,2006:122-123.
[16] ToshjiMukai, Masashi Yamanoi, Hiroyki Watanabe, Kenji Higashi.Ductility Enchancement in AZ31 Magnesium Alloy by Controllingits Grain Structure [J]. Scripta Materialia, 2001 (45):89-94.
[17]王渠东,吕宜振,曾小勤等.稀土在铸造镁合金中的应用[J].特种铸造及有色金属,1999(10): 40-43.
[18] Buch F V, Lietzau J, et al. Development of Mg-Sc-Mn alloys [J]. Materials Science and Engineering, 1991, A263: 1-7.
[19] Inoue A, Kato A, etc. Mg-Cu-Y amorphous alloys with high mechanical strengths produced by a metallic mold casting method [J]. MaterialsTransactions. JIM, 1991, 32(7):609-616.
[20]林肇琦.有色金属材料学[M].东北工学院出版社,1986.
[21] Raynond F D, Robert D C, etc. Magnesium semisolid metal forming [J]. Advanced Materials and Processes, 1996, (2):41-42.
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