挤压变形Mg-Al和Mg-Zn系镁合金的力学行为
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摘要
由于镁合金在降低产品重量、节省能源及增强产品可靠性等方面所具有的优势，镁合金的开发应用引起了人们的高度重视。近年来，随着汽车工业和电子工业的迅速发展，大量的镁合金结构件被生产出来，代替塑料、铝合金甚至钢制零件，预计镁合金将成为本世纪最重要的商用轻质金属结构材料。由于变形镁合金比铸造镁合金具有更高的强度和塑性，因此，变形镁合金已经在镁质材料的未来广泛应用中呈现出越来越大的潜力。显然，针对变形镁合金的组织、结构与性能开展研究不仅可为新型变形镁合金的开发奠定理论基础，也可为变形镁合金结构件的安全设计和合理使用提供可靠的理论依据。为此，本文主要针对不同加工处理状态的挤压变形AM50和AZ91合金的拉伸行为和低周疲劳行为进行了研究，确定了试验温度和热处理对挤压变形AM50和AZ91合金的拉伸性能和疲劳性能的影响。此外，还针对挤压变形AZ81合金以及等通道转角挤压ZK40合金的超塑性变形行为进行了研究，并探讨了试验温度对两种合金的超塑性能的影响以及相应的超塑性变形机制。
拉伸行为研究结果表明，随着试验温度的升高，不同加工处理状态的挤压变形AM50和AZ91合金的抗拉强度和屈服强度降低，而断裂伸长率则不断增大。经固溶处理(T4)的挤压变形AM50和AZ91合金的晶粒发生了长大，导致力学性能有所下降；若固溶处理后再进行时效处理(T6)，因为有弥散细小的第二相(Mg_(17)Al_(12))析出，可起到强化作用，两种合金的抗拉强度和屈服强度得以提高；热挤压后直接进行人工时效处理(T5)，可导致强化相析出，故可有效地提高AM50合金的室温和高温拉伸性能以及AZ91合金的室温拉伸性能。对不同加工处理状态的挤压变形AM50和AZ91合金的拉伸断口形貌分析显示，室温下，合金表现出韧性和脆性混合断裂特征，而在高温下，韧窝数量多且较深，可以确定合金基本发生韧性断裂。
低周疲劳行为研究结果表明，挤压变形AM50与AZ91镁合金的循环应力响应行为与外加总应变幅及其加工处理状态密切相关。在较大的外加总应变幅下，不同加工处理状态的挤压变形镁合金可表现为循环应变硬化及循环稳定；而在较低的外加总应变幅下，这些合金在疲劳变形初期常表现为循环稳定，甚至呈现循环软化，但是在疲劳变形后期则发生比较明显的循环应变硬化；固溶处理和时效处理均可在一定程度上改变挤压变形AM50与AZ91镁合金的循环应力响应行为。对于不同加工处理状态的挤压变形AM50与AZ91镁合金而言，其弹性应变幅、塑性应变幅与断裂时的反向循环周次之间的关系表现为单斜率线性行为，并分别服从Basquin和Coffin-Manson公式。在较高的外加总应变幅下，两种挤压变形镁合金的循环滞后回线上对应于压缩变形部分的宽度明
Due to their superior performances in weight reductions, energy source saving and reliability enhancement, both development and applications of magnesium alloys have been considerably focused. In recent years, with the rapid progress of automotive and electronic industries, a number of magnesium alloy components have been manufactured to replace those made of plastics, aluminum alloy and steel ones. It can be expected that magnesium alloys will become the most important lightweight structural materials in commercial metal materials. Wrought magnesium alloys can exhibit the higher strength and better plasticity than cast magnesium alloys, and show the more significant potential in further applications of magnesium based materials. Obviously, researches on microstructures and properties of wrought magnesium alloys can not only establish theoretical foundation for new development of wrought magnesium alloys, but also provide reliable bases for safe design and reasonable usage of wrought magnesium alloy components.
In this paper, the tensile and low cycle fatigue behaviors of extruded AM50 and AZ91 magnesium alloys with different processing statuses are investigated. The influence of testing temperature and heat treatment on both tensile and fatigue properties of extruded AM50 and AZ91 magnesium alloys are determined. Moreover, the superplastic deformation behavior of extruded AZ81 and equal-channel-angular-pressed ZK40 magnesium alloys has also been studied. The effect of testing temperature on the superplastic property of two alloys and corresponding superplastic deformation mechanism are discussed.
The tensile experimental results show that for the AM50 and AZ91 alloys subjected to different processing and treatment, the ultimate tensile and yield strengths decrease while elongation to failure obviously increases with increasing test temperature. After the solid solution treatment (T4), the growth of grains occurs, which leads to a decrease in mechanical properties of two alloys. When the aging is applied following solid solution treatment (T6), the ultimate tensile and yield strengths of two alloys will get enhanced because the fine secondary phase particles precipitate The aging directly following hot extrusion (T5) can result in the precipitation of those strengthening phases such as Mg_(17)Al_(12), and thus the tensile properties of the AM50 alloy at room and elevated temperatures as well as the tensile properties of the AZ91 alloy at room temperature get increased. Fracture surface analysis revealed that the extruded AM50 and AZ91 alloys with different processing statuses exhibit a characteristic of mixed ductile and brittle fracture during tension at room temperature. At
拉伸行为研究结果表明，随着试验温度的升高，不同加工处理状态的挤压变形AM50和AZ91合金的抗拉强度和屈服强度降低，而断裂伸长率则不断增大。经固溶处理(T4)的挤压变形AM50和AZ91合金的晶粒发生了长大，导致力学性能有所下降；若固溶处理后再进行时效处理(T6)，因为有弥散细小的第二相(Mg_(17)Al_(12))析出，可起到强化作用，两种合金的抗拉强度和屈服强度得以提高；热挤压后直接进行人工时效处理(T5)，可导致强化相析出，故可有效地提高AM50合金的室温和高温拉伸性能以及AZ91合金的室温拉伸性能。对不同加工处理状态的挤压变形AM50和AZ91合金的拉伸断口形貌分析显示，室温下，合金表现出韧性和脆性混合断裂特征，而在高温下，韧窝数量多且较深，可以确定合金基本发生韧性断裂。
低周疲劳行为研究结果表明，挤压变形AM50与AZ91镁合金的循环应力响应行为与外加总应变幅及其加工处理状态密切相关。在较大的外加总应变幅下，不同加工处理状态的挤压变形镁合金可表现为循环应变硬化及循环稳定；而在较低的外加总应变幅下，这些合金在疲劳变形初期常表现为循环稳定，甚至呈现循环软化，但是在疲劳变形后期则发生比较明显的循环应变硬化；固溶处理和时效处理均可在一定程度上改变挤压变形AM50与AZ91镁合金的循环应力响应行为。对于不同加工处理状态的挤压变形AM50与AZ91镁合金而言，其弹性应变幅、塑性应变幅与断裂时的反向循环周次之间的关系表现为单斜率线性行为，并分别服从Basquin和Coffin-Manson公式。在较高的外加总应变幅下，两种挤压变形镁合金的循环滞后回线上对应于压缩变形部分的宽度明
Due to their superior performances in weight reductions, energy source saving and reliability enhancement, both development and applications of magnesium alloys have been considerably focused. In recent years, with the rapid progress of automotive and electronic industries, a number of magnesium alloy components have been manufactured to replace those made of plastics, aluminum alloy and steel ones. It can be expected that magnesium alloys will become the most important lightweight structural materials in commercial metal materials. Wrought magnesium alloys can exhibit the higher strength and better plasticity than cast magnesium alloys, and show the more significant potential in further applications of magnesium based materials. Obviously, researches on microstructures and properties of wrought magnesium alloys can not only establish theoretical foundation for new development of wrought magnesium alloys, but also provide reliable bases for safe design and reasonable usage of wrought magnesium alloy components.
In this paper, the tensile and low cycle fatigue behaviors of extruded AM50 and AZ91 magnesium alloys with different processing statuses are investigated. The influence of testing temperature and heat treatment on both tensile and fatigue properties of extruded AM50 and AZ91 magnesium alloys are determined. Moreover, the superplastic deformation behavior of extruded AZ81 and equal-channel-angular-pressed ZK40 magnesium alloys has also been studied. The effect of testing temperature on the superplastic property of two alloys and corresponding superplastic deformation mechanism are discussed.
The tensile experimental results show that for the AM50 and AZ91 alloys subjected to different processing and treatment, the ultimate tensile and yield strengths decrease while elongation to failure obviously increases with increasing test temperature. After the solid solution treatment (T4), the growth of grains occurs, which leads to a decrease in mechanical properties of two alloys. When the aging is applied following solid solution treatment (T6), the ultimate tensile and yield strengths of two alloys will get enhanced because the fine secondary phase particles precipitate The aging directly following hot extrusion (T5) can result in the precipitation of those strengthening phases such as Mg_(17)Al_(12), and thus the tensile properties of the AM50 alloy at room and elevated temperatures as well as the tensile properties of the AZ91 alloy at room temperature get increased. Fracture surface analysis revealed that the extruded AM50 and AZ91 alloys with different processing statuses exhibit a characteristic of mixed ductile and brittle fracture during tension at room temperature. At
引文
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