【作者】 郝帅；

【导师】 邱克强； 尤俊华；

【作者基本信息】 沈阳工业大学 ， 材料学， 2012， 硕士

【摘要】 为了提高镁合金的耐热性能,本文在Mg-5%Sn合金中加入Si、Sr、Ca合金化元素,设计了Mg-Sn-Si-Sr系和Mg-Sn-Si-Sr-Ca系合金。采用X射线衍射仪(XRD)、光学显微镜(OM)、扫描电镜(SEM)分别研究了合金的相组成及显微组织,采用万能试验机和布氏硬度计测定了合金的力学性能,并采用SEM分析合金的断口形貌,主要结论如下:铸态Mg-5Sn-xSi-0.5Sr(x=1, 2)合金组织由α-Mg晶界析出的共晶Mg2Sn、Mg2Si相和α-Mg晶内初生MgSnSr相所组成。铸态Mg-5Sn-xSi-2Sr(x=1, 2)合金组织同样由Mg2Sn、Mg2Si和MgSnSr相所组成,与Mg-5Sn-xSi-0.5Sr(x=1, 2)合金相比,当Sr含量由0.5%增加到2%时会促进MgSnSr相形成,而抑制晶界上Mg2Sn相的析出,同时能够细化Mg2Si相。Mg2Si相含量随Si元素的增加而增加,但MgSnSr相含量随Si元素的增加而减少。在这四种铸态合金中Mg-5Sn-2Si-2Sr合金具有最好的力学性能,铸态Mg-5Sn-2Si-2Sr合金的抗拉强度、屈服强度和延伸率分别为156MPa、120MPa和5%。对于Mg-5Sn-xSi-0.5Sr-0.5Ca(x=1, 2)铸态合金,与Mg-5Sn-xSi-0.5Sr(x=1, 2)合金相比,加入Ca元素显著促进(Ca, Sr)MgSn相的形成,而抑制晶界上Mg2Sn相的析出,并能细化Mg2Si相。对于铸态Mg-5Sn-2Si-2Sr-0.5Ca合金,与Mg-5Sn-2Si-0.5Sr-0.5Ca合金相比,Sr含量由0.5%提高到2%后,Mg2Si相得到进一步细化,并在晶内析出大量的MgSn(Sr, Ca)相。铸态Mg-5Sn-1Si-0.5Sr-2Ca合金则由层片状Mg2Ca相和针状CaMgSn相所组成。在这四种铸态合金中Mg-5Sn-2Si-2Sr-0.5Ca合金具有最好的力学性能,铸态Mg-5Sn-2Si-2Sr-0.5Ca合金的抗拉强度、屈服强度和延伸率分别为153MPa、111MPa和4.3%。热处理后,合金的性能得到显著提升。Mg-5Sn-2Si-2Sr合金的最佳热处理工艺为在500℃固溶24h,200℃时效6h,热处理后Mg-5Sn-2Si-2Sr合金的抗拉强度、屈服强度、延伸率、布氏硬度分别为182MPa、151MPa、4.1%、50HB。Mg-5Sn-2Si-2Sr-0.5Ca合金的最佳热处理工艺为在500℃固溶24h,200℃时效12h,热处理后Mg-5Sn-2Si-2Sr-0.5Ca合金的抗拉强度、屈服强度、延伸率和布氏硬度分别为178MPa、142MPa、3.7%和49HB。更多还原

【Abstract】 In order to improve the heat resistant properties of Mg alloys, Mg-Sn-Si-Sr and Mg-Sn-Si-Sr-Ca alloys were designed by adding Si, Sr and Ca alloying elements to the Mg-5%Sn alloy in this paper. The phase constituent and microstructure of the as-cast resultant alloys were analyzed by using x-ray diffractometer (XRD), optical microscopy (OM) and scanning electron microscopy (SEM), respectively. The mechanical properties of the alloys were tested by universal electronic testing machine and brinell hardness tester. The fracture surfaces were analyzed by using SEM. The important results are summaried as follows:The Mg2Sn and Mg2Si phases were precipitated on theα-Mg grain boundary during eutectic reactions and MgSnSr precipitated in the grains of as a primary phase for as-cast Mg-5Sn-xSi-0.5Sr (x=1, 2) alloys. The microstructure of the as-cast Mg-5Sn-xSi-2Sr (x=1, 2) alloys are also composed of Mg2Sn, Mg2Si and MgSnSr phases. Compared with the Mg-5Sn-xSi-0.5Sr (x=1, 2) alloys, when the Sr content is increased from 0.5wt% to 2wt%, which promotes the formation of MgSnSr phase, inhibits the precipitation of Mg2Sn phase on the grain boundary, and refines the Mg2Si phase at the same time. The volume fractions of Mg2Si phase increases whereas the MgSnSr phase decreases with the addition of silicon element. The tensile strength, yield strength and elongation of the as-cast Mg-5Sn-2Si-2Sr alloy are 156MPa, 120MPa and 5.0%, respectively. Which is the best one among the four the as-cast alloys.For the Mg-5Sn-xSi-0.5Sr-0.5Ca (x=1, 2) as-cast alloys, compared with the Mg-5Sn-xSi-0.5Sr (x=1, 2) alloys, furthermore, the addition of Ca element can promote significantly the formation of primary (Ca, Sr)MgSn phase, inhibit the precipitation of Mg2Sn phase on the grain boundary, and refine the Mg2Si phase. Compared with the Mg-5Sn-2Si-0.5Sr-0.5Ca alloy, when the Sr content is increased from 0.5wt% to 2wt% for as-cast Mg-5Sn-2Si-2Sr-0.5Ca alloy, the Mg2Si phase has been significantly refined, and a large number of MgSn(Sr, Ca) phases are precipitated in intragranular. As-cast Mg-5Sn-1Si-0.5Sr-2Ca alloy are composed of Mg2Ca phase with lamellar-type and CaMgSn phase with needle-like. The tensile strength, yield strength and elongation of the as-cast Mg-5Sn-2Si-2Sr-0.5Ca alloy are 153MPa, 111MPa and 4.3%, respectively. Which is the best one among the four the as-cast alloys.The mechanical properties of the alloys have been significantly improved after heat treatment. The most suitable heat treatment process for Mg-5Sn-2Si-2Sr alloy is solution 24h at 500℃and then aging 6h at 200℃. The tensile strength, yield strength, elongation and brinell hardness of Mg-5Sn-2Si-2Sr alloy are 182MPa, 151MPa, 4.1% and 50HB respectively after heat treatment. While the most suitable heat treatment process for Mg-5Sn-2Si-2Sr-0.5Ca alloy is solution 24h at 500℃and then aging 12h at 200℃. The tensile strength, yield strength, elongation and brinell hardness of Mg-5Sn-2Si-2Sr-0.5Ca alloy are 178MPa, 142MPa, 3.7% and 49HB respectively after heat treatment.更多还原