【作者】 李涛；

【导师】 张新明； 戚文军；

【作者基本信息】 中南大学 ， 材料科学与工程， 2013， 硕士

【摘要】 本课题的研究目的是改善Mg-Al系镁合金的耐热性能,开发—种新型低成本、高强度的含稀土耐热镁合金。以Mg-6A1镁合金为研究对象,通过合金的设计与制备,运用扫描电子显微分析、X射线衍射分析和电子拉伸试验等材料现代分析和测试手段,系统地研究了添加合金元素Sm、Bi和Zn对Mg-6A1镁合金显微组织和力学性能的影响,并研究了压铸工艺对几种铸态性能较好的Mg-Al系镁合金显微组织和力学性能的影响。研究结果表明：适量Sm、Bi和Zn元素的添加能显著改善Mg-6A1合金的室温(25℃)和高温(150℃)下的铸态组织和力学性能。压铸工艺能改善Mg-6Al系合金的显微组织和力学性能。在Mg-6A1镁合金中加入0.5wt%-3.0wt%Sm后,合金的铸态组织中出现弥散分布的颗粒状新相Al2Sm,分布在晶界和晶内。随着Sm含量的增加,铸态合金的在室温和高温下的抗拉强度和延伸率呈先升后降的规律。室温下,在1.0wt%Sm时抗拉强度和延伸率达到最大值,分别为220MPa、12.5%；高温下,当Sm含量为1.0wt%Sm时,抗拉强度和延伸率分别为169MPa和25.5%。在Mg-6Al-1Sm合金中加入0.5-1.5wt%Bi后,合金中的Mg17Al12减少,在晶界和晶内析出了高熔点的长条状的Mg3B12相和颗粒状的Al2Sm相。随着Bi含量的增加,基体中的长条状的Mg3Bi2相和颗粒状的Al2Sm相变得粗大,并且部分产生偏聚。室温下,Bi元素对Mg-6Al-1Sm合金的抗拉强度和延伸率提升效果不明显,高温(150℃)时,Bi对合金组织及力学性能的改善效果显著,在0.75wt%Bi时,抗拉强度和延伸率达到最大值184MPa和23.5%。在Mg-6Al-1Sm合金中加入0.5～1.5wt%Zn后,Mg-6Al-1Sm-xZn合金的金相显微组织中没有新增加其他第二相,但是Mg17Al12相数量明显增多,主要沿晶界分布,可知Zn元素的添加没有形成新的第二相,而是固溶于基体或其他第二相中。在25℃和150℃下,随着Zn元素的增加,抗拉强度呈先增加后降低趋势。25℃时,添加0.5wt%Zn的合金的抗拉强度达到最大值235MPa；150℃时,添加0.75wt%Zn的合金的抗拉强度和延伸率达到最大值175MPa和20.0%,延伸率提升效果显著。压铸态合金组织比铸态合金组织更加致密,晶粒更加细小,抗拉强度更加高。Sm元素能有效降低合金压铸组织中的气孔和夹杂数量。室温拉伸性能最好的是Mg-6Al-1Sm合金,抗拉强度为285Mpa,延伸率为16.5%。150℃下,Mg-6Al-1Sm-0.5Zn的综合性能最好,其延伸率为17.5%,提高幅度为118%。实验合金在铸态时流动性能均优于AZ91D,其中Mg-6Al-1Sm-1.0Zn的流动性最好,流动长度达到了520mm。而压铸态时集中实验合金的流动性能接近AZ91D,其中,Mg-6Al-1Sm-0.5Bi合金和Mg-6Al-1Sm-1.0Bi合金两者的流动长度分别为2420mm和2390mm。更多还原

【Abstract】 The purpose of the research is to develope of a new low-cost, high-strength rare-earth heat-resistant magnesium alloy by improving the heat resistance of Mg-Al based alloys. The effect of Bi、Zn and rare earth Sm on microstructures and mechanical properties of Mg-6Al magnesium alloy have been investigated by optical microscopy, scanning electron microscopy, X-ray diffractometer and electronic tensile test.And the effect of the die-casting on microstructure and mechanical properties of the cast alloys has been investgated. The results show that:The appropriate amount addition of Sm, Bi, and Zn has significantly improved the as-cast microstructures and mechanical properties of Mg-6A1alloy at room temperature and high temperature. The die-casting has improved the microstructures and mechanical properties of Mg-6A1alloy.For the Mg-6A1magnesium alloy with0.5wt%-3.0wt%Sm, cast microstructures appear dispersed phase Al2Sm, distributing in the grain boundary and grain interior. With increasing content of Sm, the tensile strength and elongation first increase, then decrease. At room temperature, when content of Sm is1.Owt%, the mechanical properties and elongation are up to the maximum,i.e.220MPa、12.5%. At high temperatures, when the content of Sm is1.Owt%, the mechanical properties and elongation are169MPa and25.5%,respectively.For Mg-6Al-1Sm alloy with0.5～1.5wt%Bi, the Mg17Al12phase reduces, and Mg3Bi2and Al2Sm phases have formed. With increasing content of Bi, Mg3Bi2and Al2Sm phases become thick, produce segregation partly. At room temperature, the effect of Bi on tensile strength and elongation is not obvious. At high temperature (150℃), Bi significantly improves tensile strength and elongation. When content of Bi is0.75wt%,the tensile strength and elongation reaches maximum184MPa and23.5%For the Mg-6Al-1Sm alloy with0.5～1.5wt%Zn, Mg17Al12phases have incresed, and distrubuted along the grain boundaries. Zn solid solution in the matrix or other second phases. At25℃and150℃, with increasing content of Zn, tensile strength first increase, then decrease. At25℃, the mechanical properties of the cast-alloy which added0.5wt%Zn are up to its maximum235MPa; At150℃, the mechanical properties and elongation reaches their maximum175MPa and20.0%. The elongation is improved abviously.Die-cast alloy tissue is more dense than the cast alloy, the finer the grain, the higher tensile strength. Sm element can effectively reduce the number of pores and inclusions in the alloy die-casting. Mg-6Al-1Sm alloy has the best room temperature tensile properties, i.e. tensile strength285MPa, elongation16.5%. At150℃Mg-6Al-1sm-0.5Zn have the best comprehensive properties, and its elongation is17.5%, which increased by118%.The flow properties of the experimental cast alloys are better than AZ91D, Mg-6Al-1Sm-1.0Zn has the best liquidity,up to520mm. Flow properties of die-cast alloy are close to AZ91D, the flow length of Mg-6Al-1Sm-0.5Bi and Mg-6Al-1Sm-1.0Bi are2420mm and2390mm respectively.更多还原