【作者】 王晓明；

【导师】 张金山；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2008， 硕士

【摘要】 Mg-Al-Zn镁合金是目前使用最广泛的镁合金系列之一,但阻碍该系合金进一步应用的主要问题有:①铸造镁合金（如AZ91D等）的高温抗蠕变性能差,长期工作温度不能超过120℃,无法用于制造对高温蠕变性能要求高的零部件;②变形镁合金（如AZ31等）的常温塑性加工性能差,无法满足不同场合的使用要求。为了解决Mg-Al-Zn镁合金目前存在的问题,人们正从合金化、晶粒细化、热处理和熔体处理等方面对该系合金展开研究,以期开发出高性能的新型Mg-Al-Zn镁合金。由于合金组织决定性能,因此研究Mg-Al-Zn镁合金在不同条件下合金相的形成和转变规律对于高性能新型Mg-Al-Zn镁合金的开发意义重大。本文采用金相分析、扫描电镜（SEM）、能谱（EDS）分析、X-衍射分析（XRD）等实验手段,研究了不同Al、Zn含量的Mg-Al-Zn合金组织中合金相种类、形态、数量和分布的变化规律,选定一种韧度较高,综合性能较好的合金（Mg-5%Al-4%Zn（wt%））作为研究的基础,同时研究了Mg-Zn-Y-Mn球形准晶对选定的Mg-5%Al-4%Zn（wt%）合金组织和性能的影响,以期为高性能新型Mg-Al-Zn基镁合金开发过程中合金相的控制以及化学成分和工艺的优化设计提供组织控制依据。本文研究结果表明:Mg-Al-Zn镁合金的铸态组织由初生相α-Mg和第二相组成,其中第二相的形态主要有骨骼状、块状、颗粒状和片层状等形态,其大多分布在晶界处,少量分布在晶内;Al、Zn含量变化对Mg-Al-Zn基镁合金中化合物的数量和分布有非常明显的影响,当Al或Zn含量增加时,初生相α-Mg减少,而化合物的数量明显增多,并变得连续;在Mg-5%Al-X%Zn（X≥3）合金中,随着Zn含量的提高,τ(Mg₃₂（Al,Zn）₄₉)相逐渐增多,φ（Al₂Mg₅Zn₂）相逐渐减少。Mg-5%Al-4%Zn（wt%）铸态综合性能较高:韧度14.3J/cm²,强度155.7MPa,布氏硬度65.53。通过设计正交回归实验,得出了Y和Mn含量与单位面积内准晶尺寸以及数量的二次回归关系式,绘出直观的三维图,综合金相组织形貌,结果显示:在Mn含量确定的情况下,准晶的数量随着Y含量的增加而增加;Mn的含量对准晶的数量影响较小,但较少的Mn可以从一定程度上促进准晶的生成,反之Mn的含量过高则抑制准晶的形成;Mn、Y含量二者的交互作用对准晶尺寸影响较大,Mn的含量如果相对较低,那么Mn作为准晶生长核心的作用比较突出,但球化效果不足,准晶数量多,但尺寸大,当Mn元素相对含量较高时,造成界面不稳定,又促使准晶向花瓣状生长,尺寸也大。当Y添加量3.9%～4.0%,Mn 4.0%～4.3%（wt%）时,获得的准晶较好。Mg-5%Al-4%Zn（wt%）合金中加入Mg-Zn-Y-Mn中间合金之后,合金凝固后的铸态组织由α-Mg相+τ(Mg₃₂（Al,Zn）₄₉)相+φ（Al₂Mg₅Zn₂）相+i(Mg₄₅Zn₄₇Y₃Mn₅)相组成;镁基准晶中间合金的加入不仅使基体组织细化,而且使τ(Mg₃₂（Al,Zn）₄₉)相由网状分布变为断网分布,甚至颗粒化;合金的室温和高温（200℃）力学性能得到了大幅度的提高,当加入2.5%的MZYM后,合金的冲击韧度提高了28.2%,达到18.3J/cm²;加入3.5%的MZYM后,合金的抗拉强度提高了16.4%,达到了181.2MPa;加入5.5%的MZYM后,合金的高温（200℃）抗拉强度较AZ54母合金提高了18.1%,达到了166.5 MPa。对添加准晶中间合金后的AZ54合金热处理研究结果表明:经T4处理后,τ(Mg₃₂（Al,Zn）₄₉)相和φ（Al₂Mg₅Zn₂）相部分固溶于α-Mg基体中,准晶颗粒相在形貌上没有太大变化;经T6热处理后,合金组织中重新析出τ(Mg₃₂（Al,Zn）₄₉)相,但其数量、尺寸与形貌有所不同,准晶中间合金的加入延长了τ(Mg₃₂（Al,Zn）₄₉)相的析出时间,而且抑制了τ(Mg₃₂（Al,Zn）₄₉)相的非连续析出;经T6热处理后,合金的室高温力学性能明显提高,室高温（200℃）抗拉强度分别比铸态合金提高了30.96%,28.36%,达到了237.3MPa,199.6MPa;室温下布氏硬度达到97.5,比原来提高了44.4%;韧度有所下降。更多还原

【Abstract】 Mg-Al-Zn based alloys are one of the most widely used magnesium alloy series currently,but at present what blocks it from further utilization is as follows:①Casting magnesium alloys（for example AZ91D）suffers from low creep resistance at temperatures above 120℃,which makes it unsuitable for many of components that requiring excellent creep resistance at high temperature;②Wrought magnesium alloys（for example AZ31）have poor plastic deformation property at room temperature,so they can not meet different needs in different situations.In order to solve the existing problems of Mg-Al-Zn based magnesium alloys,lots of research about alloying,grain refinement,melt treatment and heattreatment and so on,had been carried out to improve the properties.Because the properties of alloys are determined by their microstructures,it is of great importance to carry out investigation on the microstructure of Mg-Al-Zn based magnesium alloys,especially mechanism of forming and transforming of alloy phases in Mg-Al-Zn based magnesium alloys. The morphology,category,amount and distribution of alloy phases in the Mg-Al-Zn magnesium alloys with different amount of Al and Zn were investigated.Choosing AZ54 alloy with better property as the based alloy and the effects of the addition of spherical Mg-Zn-Y-Mn quasicrystal on the microstructure and mechanical properties of Mg-5%Al-4%Zn（AZ54）were investigated by metallurgical phase analysis,scanning electron microscopy （SEM）analysis,XRD analysis and energy diffraction（EDS）analysis in this paper.The research results that can be used to guide the alloy phases controlling and the optimization of composition and processing parameters that expected to obtain.The research results indicate that:The microstructure of the casting Mg-Al-Zn magnesium alloys consists of the matrix（α-phase）and the second phases whose morphology are bone-like, lump-like,particle-like and layer-like,they mainly distribute at grain boundaries and only a few are inside the grains;The change of Al and Zn content has very obvious effect on the amount and distribution of alloy phases,With the increase of Al or Zn content,the amount of primaryα-phase decrease,the amount of compounds increases and their distribution become more continuous;In Mg-5%Al-X%Zn（X≥3）alloy,the amount ofτ(Mg₃₂（Al,Zn）₄₉)phases increase with the increase of Zn addition,while theφ（Al₂Mg₅Zn₂）phases decrease.The mechanical properties of Mg-5%Al-4%Zn cast alloy at room temperature is:The impact toughness is 14.3J/cm²,impact tensile strength is 155.7MPa and brinell hardness is 65.53.By orthogonal design,we acquire a relationship between the addition of Mn,Y and the size&amount of quasicrystals.According with the microstructure, the result indicate:In the circumstances that Mn is confined,the amount of quasicrystals increase with the increase of amount of Y,to a certain extent,less Mn can promote the quasi-crystal formation,though the effect of Mn on the number of quasicrystal is little.On the contrary the Mn High it will inhibit the formation of quasicrystals.Mn,Y and the interaction of the two make a great impact on the size of quasicrystals.If the addition of Mn is relatively low,Mn plays a core role in the process of spherical Quasicrystals’ growth,as a result, the size of Quasicrystals is large.On the contrary,relatively high amount of Mn can cause an instable interface and lead the quasicrystals to grow like a petal, and its size become larger.When the addition of Y is 3.9%～4.0%and Mn 4.0%～4.3%,we can acquire better quasicrystals.After Mg-Zn-Y-Mn master alloy being added into Mg-5%Al-4%Zn alloy, the microstructure of AZ54 cast alloy are consisted of matrixα-Mg phases,τ(Mg₃₂（Al,Zn）₄₉)phases,φ（Al₂Mg₅Zn₂）phases and i(Mg₄₅Zn₄₇Y₃Mn₅)phase. The matrix microstructure of AZ54 alloy can be refined obviously by the addition of quasicrystal master alloy,and the morphology ofτ(Mg₃₂（Al,Zn）₄₉) phases andφ（Al₂Mg₅Zn₂）phases on the grain boundaries changes from continuous net shape to discontinuous shape,even to particles.When 2.5% MZYM master alloy being added,the impact toughness enhanced by 28.2%, reach to 18.3J/cm²;after 3.5%MZYM being added,the tensile strength at room temperature enhanced by 16.4%,reach to 181.2MPa;when the addition of MZYM reached to 5.5%,the ultimate strength at temperature of 200℃of AZ54 alloy respectively increase by 18.1%,reach to 166.5MPa.The results of heattreatment on AZ54 alloy with addition of Mg-Zn-Y-Mn master alloy show that:after solution treatment,part of theτ(Mg₃₂（Al,Zn）₄₉) phases andφ（Al₂Mg₅Zn₂）phases dissolve into the matrix,and the morphology of quasicrystal phase didn’t obviously change.After aging treatment,theτ(Mg₃₂（Al,Zn）₄₉)phases were precipitated again,but the amount,size and morphology changed.The addition of quasicrystal master alloy to AZ54 alloy prolongs precipitation time of theτ(Mg₃₂（Al,Zn）₄₉)phases,and suppressed the discontinuous precipition.In aging temper,the mechanical properties of alloys promote obviously at room temperature and elevated temperature are significantly improved.Compared with AZ54 alloy,the ultimate strength at room temperature and elevated temperature of 200℃of AZ54+3.5%MZYM alloy,increase by 30.96%and 28.36%,reach to 237.3MPa and 199.6MPa respectively.Macrohardness at room temperature increase by 44.4%,reach to 97.5.But impact toughness decreases.更多还原