【作者】 李媛媛；

【导师】 李锋；

【作者基本信息】 沈阳工业大学 ， 材料学， 2005， 硕士

【摘要】 本文研究了经过热挤压变形的AZ91和AM50镁合金的拉伸力学行为,确定了其在不同实验温度及热处理状态下的抗拉强度σ_b、屈服强度σ_0.2及断裂延伸率δ,探讨了热挤压和热处理所引起的AZ91和AM50镁合金的微观组织演化,并利用扫描电镜对拉伸断口形貌进行了分析,进而了确定了实验温度和热处理对热挤压镁合金的力学性能及其断裂特征的影响。此外,还研究了熔体中添加含碳细化剂后的AZ61镁合金在铸态和固溶处理状态下的组织以及力学行为。 研究结果表明:热挤压可以显著细化铸态AZ91和AM50镁合金的晶粒,提高镁合金AZ91和AM50的室温综合力学性能。实验温度对镁合金的拉伸性能有显著影响,一般地,随着实验温度的升高,不同处理状态的AZ91、AM50镁合金的抗拉强度和屈服强度降低,而断裂延伸率则不断升高。热处理对挤压态镁合金的力学性能也有较大的影响,经固溶处理（T4）的热挤压AZ91和AM50镁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(Mg₁₇Al₁₂)析出,可起到强化基体的作用,室温下两种合金的抗拉强度和屈服强度仍然要比T4态的要高;热挤压后直接进行人工时效处理（T5）,可导致合金组织均匀化以及强化相沿着晶界析出,故可有效地提高AZ91镁合金的室温综合力学性能以及AM50镁合金的室温和高温拉伸性能。在AZ61镁合金熔体中添加适量的C₂Cl₆可以改善合金的铸态组织,并获得良好的室温力学性能,而其后的固溶处理可对铸态AZ61镁合金的室温拉伸性能产生不同程度的影响。 对不同加工处理状态的镁合金的断口形貌的分析显示,在室温下拉伸时,镁合金表现出韧性和脆性混合断裂特征;而在高温下拉伸时,韧窝数量多且较深,可以确定合金基本发生韧性断裂。更多还原

【Abstract】 In this paper, the mechanical properties of as-extruded AZ91 and AM50 magnesium alloys were investigated. The ultimate tensile strength σ_b, 0.2% offset yield strength σ₀.2 and elongation to failure 5 of two extruded magnesium alloys at different test temperatures and under various heat treatment conditions were obtained. The evolution in the microstructure of as-extruded AZ91 and AM50 magnesium alloys due to hot extrusion and heat treatment were studied. By means of SEM, observations on fracture surfaces were carried out. And the effect of test temperature and heat treatment on the mechanical properties and fracture mechanism of as-extruded magnesium alloys were determined. Moreover, the microstructure and mechanical properties of the as-cast and heat-treated AZ61 magnesium alloys with an addition of C2Cl6 in magnesium alloy melt were also studied.The results showed that the hot extrusion processing could significantly reduce the grain size of as-cast AZ91 and AM50 magnesium alloys, and thus enhance the mechanical properties of those alloys at room temperature. The influence of test temperature on mechanical properties of the magnesium alloys subjected to different processing and treatment was obvious. In general, with increasing test temperature, the ultimate tensile strength and yield strength decreased while elongation to failure increased obviously. This can be mainly attributed to an increase in number of slip systems of the matrix with test temperature. The considerable effect of heat treatment on mechanical properties of as-extruded AZ91 and AM50 magnesium alloys was also noted. After solid solution treatment （T4）, the growth of grains and the partial solution of those strengthening phases in the extruded AZ91 and AM50 alloys occurred, which led to a decrease in mechanical properties of two alloys. When the aging was applied following the solid solution treatment （T6）, the ultimate tensile and yield strengths of two alloys at room temperature would become higher because the fine secondary phase particles precipitated and the matrix got reinforced. The aging directly following hot extrusion （T5） could result in the uniform microstructure and the precipitation of those strengthening phases such as Mg₁7Al₁2, and thus the mechanical properties of the AZ91 alloy at room temperature as well as the tensileproperties of the AM50 alloy at room and elevated temperatures got enhanced.It was also found that adding a appropriate amount of C₂Cl₆ into the AZ61 alloy melt would improve the microstructure of as-cast AZ61 alloy and enhance the mechanical properties of the alloy at room temperature. The solid solution treatment performed along with the addition of C₂Cl₆ could also give an influence on the mechanical properties of as-cast AZ61 alloy at room temperature.Fracture surface analysis revealed that the magnesium alloys subjected to different processing and treatment exhibited a characteristic of mixed ductile and brittle fracture during tension at room temperature. At elevated temperatures, the more and deeper dimples could be observed on the fracture surfaces of the tension deformed magnesium alloys. It implied that the tensile fracture of the alloys occurred basically in a ductile mode.更多还原