Mg-Al合金晶粒细化工艺及机理研究

发布时间：2018-03-07 04:31

  本文选题：ZM5镁合金　切入点：晶粒细化　出处：《中北大学》2017年硕士论文　论文类型：学位论文

【摘要】：Mg-Al系合金是目前应用最为普遍的镁合金,目前已广泛应用于电子、航空航天、汽车等领域,在未来也有更好的应用前景。ZM5镁合金作为Mg-Al系合金的典型代表,以其优良的性能而受到越来越多的关注。但其结晶温度较宽、体积收缩率大,有明显的晶粒粗化趋势,易产生缩松、热裂等缺陷,严重制约了镁合金的发展。晶粒细化能显著提高镁合金材料的综合力学性能和铸造性能,大大改善镁合金的加工性能。本文主要以ZM5镁合金为研究主体,采用光学显微镜(OM)、扫描电子显微镜(SEM)、能谱(EDS)等手段对Mg-Al合金晶粒细化工艺及机理进行研究,主要探讨了不同的冷却速度和不同碳质变质剂及不同加入量对ZM5镁合金显微组织和力学性能的影响,并探索其细化机理。研究不同冷却速率(包括金属型铜模、金属型钢模,含10mm厚和20mm厚冷铁的阶梯型树脂砂型模具)对ZM5镁合金微观组织和力学性能的影响规律,分析计算冷却速率与晶粒尺寸以及综合力学性能之间定量关系式,探索其细化规律。结果表明,随着冷却速度的不断增大,ZM5镁合金的晶粒得到明显细化,性能也变得更加优良。在金属型铜模铸造条件下,其冷却速度最快,为7.88℃/s,其晶粒尺寸最为细小,为70.31μm;在砂型阶梯模中,由各区域由薄到厚依次为Ⅰ区、Ⅱ区、Ⅲ区,在砂型Ⅲ区(含10mm厚的冷铁)中,其冷却速度最慢,为2.94℃/s,晶粒尺寸也最为粗大,为166.43μm。其晶粒尺寸由166.43μm减小到70.31μm,减小约2.5倍。其第二相的形状由连续的网状、长链条状、块状逐渐变成不连续的雪花状、针状、颗粒状。ZM5镁合金的力学性能得到显著提高。其硬度值由54.6HB提高到66.8HB,增幅达22%;抗拉强度由165MPa提高到225MPa,增幅达36%;延伸率由2.2%增加到3.5%,增幅达59%;晶粒尺寸(D)、抗拉强度(Rm)、硬度(HB)、延伸率(A)冷却速率的定量关系为:D=221.33v-0.333,Rm=exp(5.21932-0.07165v+0.01246v2),HB=exp(4.05024-0.03v+0.00655v2),A=exp(0.84396-0.002579v+0.00948v2)。研究不同碳质变质剂(包括C2Cl6、Al-5Ti-0.8C中间合金、MnCO3)及不同加入量对ZM5镁合金组织和性能的影响规律。实验结果表明,变质剂的加入,对镁合金起到不同程度的细化作用。C2Cl6、Al-5Ti-0.8C、MnCO3三种变质剂的最佳加入量为:1.5%、2.4%、0.5%,其平均晶粒尺寸由未变质的188.86μm分别减少到75.87μm、90.34μm、103.75μm,抗拉强度较未添加的分别增加了16.2%(铸态)、39.0%(T6热处理态);5.9%(铸态)、36.6%(T6热处理态);5.4%、19.5%;伸长率分别增加了25.0%(铸态)、66.7%(T6热处理态);42.8%、70.0%;17.9%、26.7%。细化效果最为明显的是C2Cl6,其次是Al-5Ti-0.8C,然后为MnCO3。采用SEM和EDS对三种碳质变质剂的细化机理进行分析讨论。研究结果表明,C2Cl6的加入,在镁合金熔体中可能生成Al4C3颗粒,其可作为α-Mg的有效形核核心,有效提高其形核率,使晶粒得以细化;添加Al-5Ti-0.8C中间合金,在镁合金熔体中可能生成TiC和Al4C3两种颗粒,可作为α-Mg基体的有效形核核心,进而促进晶粒细化;加入MnCO3,一方面是由于镁合金熔体在反应过程中可能生成Al4C3颗粒,可作为异质形核的核心,另一方面,由于C、Mn元素的引进,其富集于晶界,引起成分过冷,增加其在形核过程中的过冷度,使晶粒得以细化。
[Abstract]:Mg-Al alloy is one of the most common magnesium alloy, has been widely used in electronics, aerospace, automotive and other fields, in the future also has a better application prospect of magnesium alloy.ZM5 as a typical representative of Mg-Al alloy, with its excellent performance and has attracted more and more attention. But the crystallization temperature is wide a large, volume shrinkage, grain coarsening tendency is obvious, easy to produce the shrinkage, cracking and other defects, which seriously restrict the development of magnesium alloy. The grain refinement can significantly improve the mechanical properties and casting properties of magnesium alloy materials, greatly improve the processing performance of magnesium alloy. In this paper, taking ZM5 magnesium alloy as the research the main body, using optical microscopy (OM), scanning electron microscopy (SEM), energy spectrum (EDS) were studied by means of the process and mechanism of grain refinement of Mg-Al alloy, mainly discusses the different cooling rate and different carbonaceous modificator and different The influence of adding on Microstructure and mechanical properties of ZM5 magnesium alloy, and explore its refinement mechanism. Research on different cooling rate (including metal mold, metal mold steel, with 10mm thickness and 20mm thick cold iron ladder type resin sand mould) influences on Microstructure and mechanical properties of ZM5 magnesium alloy. Calculation and analysis of the quantitative relationship between cooling rate and grain size and mechanical properties, to explore the law of refinement. The results showed that with the increasing of the cooling rate, the grain of ZM5 magnesium alloy was refined, performance is more excellent. The metal type copper casting condition, the cooling speed is 7.88 DEG C, /s most small, the grain size of 70.31 mu m; in the sand mold in each region by step, from thin to thick in area I, II, III, in the sand area III (with 10mm thick cold iron), the cooling speed of the slowest, 2.94 degrees for /s crystal The grain size of the coarse, 166.43 M. the grain size from 166.43 m reduced to 70.31 m, reduced by about 2.5 times. The second phase is shaped by continuous mesh, long chain, massive gradually become discontinuous snowflake, acicular, mechanical properties of granular.ZM5 magnesium alloy has been improved. The hardness increased from 54.6HB to 66.8HB, an increase of 22%; the tensile strength increased from 165MPa to 225MPa, an increase of 36%; the elongation rate increased from 2.2% to 3.5%, an increase of 59%; the grain size (D), tensile strength (Rm), hardness (HB), elongation (A) quantitative relationship between cooling speed rate: D=221.33v-0.333, Rm=exp (5.21932-0.07165v+0.01246v2), HB=exp (4.05024-0.03v+0.00655v2), A=exp (0.84396-0.002579v+0.00948v2). Research on different carbonaceous modificator (including C2Cl6, Al-5Ti-0.8C alloy, MnCO3) and effects of different additions on Microstructure and properties of ZM5 magnesium alloy. The experimental results 琛ㄦ槑,鍙樿川鍓傜殑鍔犲叆,瀵归晛鍚堥噾璧峰埌涓嶅悓绋嬪害鐨勭粏鍖栦綔鐢，

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